How gas furnace pressure switches work
Вставка
- Опубліковано 31 лип 2024
- Explanation of the gas furnace pressure switch. Disassembly of switches with a description of the parts. The use of the pressure switches as a control to monitor conditions in the combustion chamber are covered. Troubleshooting of pressure switch related problems.
This video is part of the gas furnace series of training videos made to accompany my website: www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages and fuels used can be lethal and can cause a fire or explosion. Know your limits. - Навчання та стиль
That little grey piece in the second pressure switch, snapped clear in half for me. Took the tube off and pieces of it fell out. Had no idea what it was, nobody had any idea and your video solved the mystery!
I love sitting back with a beer and spending an hour or two watching your videos! Great Job!
Ed L I will not have this type of conversation on my site. You are gone.
GFM
You just might have the best HVAC explanation/education videos on UA-cam.
I watched a few of your videos and I came to the conclusion that my pressure switch was sticking due to moisture contamination. I recently had a drainage problem which caused water to back up and leak from the inducer motor. I even had water come out of the vacuum tube where it connects to the inducer. Before replacing the pressure switch I would get an error code for stuck shut, and most recently I got a code for stuck open. I replaced the switch last Friday and the furnace been running fine since then.
Thanks for making these videos.
I sure do appreciate the specific info you gave on these pressure switches between you and my control board I fixed the problem without calling the repairman and saving me hundreds of dollars. What you are doing is great for people!!! K
Keep up the great info!
your one of my favorites, thank God for you tube and people like you that give your time to help others.
Thanks for the support
GFM
Very well done. Thorough and intelligent, extremely helpful.
Gray, very informative video. Thanks for posting
I had a call years ago with pressure switch issues. It was a two pipe system that was in a basement and the pipes were in a sheetrock cavity. After a bit of calculating, the 2" pipe was just a bit too long with the amount of elbows being used. It needed 3". I had no choice but to make both pipes into exhaust pipes.
It cured the problem but not my favorite choice.
Your videos saved me $$$$$$ much thanks!!!!! I had a kink in my water drain line. I was able to clean it and clean the pressure switch and avoid a service call. Thanks again!!!!
kmonnier Welcome
GFM
Thank you! My intake was covered with snow, so I had PV errors. Now it's working!
Welcome
GFM
Great tutorial, explained how to measure pressure as water column. I have seen magnehelic gauges to measure air flow. Nice Video !
Thanks for the support.
GFM
Very helpful tutorial on pressure switches. Thank you!
Welcome
GFM
hey gray it was the metal bib that comes out from the blower to the pressure switch.it had a little rust in it i blew it out and took the hose off and blew that small little hose out then reattached and bam! the furnace started! thanks for the info probably saved me $300.00!
I am getting addict to your videos you are the best
Thanks for the support.
GFM
thanks for the information I did it and it's working now thank so much!!!
Thanks GSM. Thanks for all the help.
Regards,
John
Man you rule! I love these videos so much!
Thanks for the support
GFM
I came home today and my furnace was short cycling. I watched your video...cleaned the fire rod with some steel wool, and it's purring like a kitten : ) Thanks for the useful info.
Lol, "FIRE ROD" that is a Flame sensor..Haha. Glad you got er' fixed though!
HEY! I WOULD LIKE TO SAY THANKS FOR YOUR HELP. I WAS READING SOME OF YOUR COMMENTS AND HEY HELPED ME WITH MY FURNACE, I HAVE A ARMSTRONG AND 3 FLASHES WERE COMING ON, WELL FIRST I DID REPLACED THE PRESSURE SWITCH, BUT NOW I KNOW IT WAS NOT THAT. VENT TUBE WAS ABSTRUCTED, I TAPPED ON IT A FEW TIMES AND THE FURNACE CAME. ON.
Thanks your explication helps a lot of people like me
Welcome
GFM
very good video well explained thank you
It means there is not enough vacuum in the heat exchanger to safely start the burner. Look at some of the comments below for what to look for. Hope this helps.
GFM
Skipped the grommet if there ever was one. Cleaned all 7 screws with wire brush and replaced two of them with standard machine hex head screw (the two that also hold on the P/s) 10-32 thread. No leaks. Igniter only starts with front and rear hoses on the new design P/s reversed from that of the original design. I am tempted to run it that way. No heat or hot water for six days so far. Thanks again for all the help GSM.
Good info. The old Goodmans seemed to be the worst for that. Thanks a lot for the comment.
GFM
You need to be sure the sensing tube is clear and all fittings are clear. Also be looking for blockages in the vent pipe. Sometimes, the inducer blower wheel can get dirty. Hope this helps.
GFM
Thanks for the thoughts.
GFM
Thanks much. Very happy for the easy fix
Welcome
GFM
holy shit ! ! it all makes sense now!! thanks a ton GFM
Glad it works.
GFM
One of the failures of most of us techs has been the use of a digital manometer. If we check the pressure and it is up to par (you need the factory specs for this), the pressure switch has failed. If not, obviously the problem is elsewhere. It is that simple. Hope this helps.
GFM
On a hk06nb124 which side is the collector and which side is burner? One of them has a grey plug in them.
Gray, today i saw a furnace that has 2 pressure switches for the 2 gas stages. these were normally open. but there is one that connects to a condensate trap and this switch is normally closed. it says 1.0wc PR. the other two says PF. is the 1.0wc PR normally closed? thank you.
thank you...
I would be looking for rust in the fitting on the inducer. Just to make sure it continues to run.
GFM
Hi GFM, having some problems with a Goodman furnace. Works fine first cycle...igniter glows, gas clicks and turns on and the burners ignite and brings thermostat up to temp, that is when the problem starts. The next cycle the igniter glows but shuts off just a second before gas comes on, this will happen 3 times then nothing for a few hours unless I flip the power switch them it will work fine for the first cycle everytime. Basically when I want it to run I flip the switch. I have replaced the circuit board, the pressure switch and cleaned the flame sensor......any ideas?
There are 4 things I can think of. Blockage in vent, inducer failing, pressure switch/ pressure line, cracked heat exchanger. I have a number of videos that may help. Hope this helps.
GFM
Good info GFM
It may fix itself. The pressure switches bleed a small amount of air in to keep the switch and line clear. The old switch may have that feature plugged. If the furnace is in an unconditioned space, it may gather moisture because of where it is. Hope this helps.
GFM
Thanks. I appreciate that.
GF>
good job
Thanks for the support.
GFM
I had 3 blinking green lights telling me the combustion pressure switch failed to close.So i watched your video and gave the switch a tap ( a light knock) and the hose leaded to the switch......and well-ahh the furnace fired up. I'm assuming dirt in the system. Will inspect in the morning....at least I have heat for the night. Save a pile of money calling a service guy at double rate. That would painful for a $40 part. But like you said, could be something in the system....cheers thanks for the video!
+Mcbeth2pl Merry Christmas
GFM
Good first view. I helped design all you are showing. Over pressure for the old switches is .5 PSI, the new plastic ones are 3 PSI and have a hard stop. The pressure rating you are seeing is NOT the test pressure in all cases. If it states PF (pressure fall) then you need to add approx. .10"WC to the reading to assure the appliance has Minimum System Pressure. The one's with a Min/Max show the "sour point" (low) and the high reading is the Minimum System pressure (high). You should always check the "bleed hole" is clear if you are getting water (condensate) in the Neg line. All new switches are required to have the set point on the switch in some manner. Also, the MFG'r WILL NOT warranty the switch if the Tamper Seal is broken.
Grant Edwards All good info. The part about the tamper seal is also good. If I saw one I always replaced with a new factory switch. For a while manufacturers did not want us to know at what pressure their switches made. Very frustrating for a service tech. And of course pressure were (and still are) blamed for any number of failures. Again, thanks for the thoughts.
GFM
The Fieldpiece Dual-Port Manometer - SDMN5 is a top quality tool. It should have dual port and Fieldpiece is a quality brand. Not that there are not others, I have a cheap GSI that works well but is not as tough as the fieldpiece. (also check the vid on comparing manometers). I would not go for the Magnehelic because you will need 2 or more and they are somewhat delicate. The water tube ones are not accurate enough. Hope this helps.
Checked Amazon for the GSI and although discontinued the Pyle PDMM01 looks identical in every way except for the name so will probably order that one. I think I found problem. I can feel air coming out from the blower housing cover plate that the motor and blower wheel are attached to. The sealant almost looks like it melted and dripped. Will remove, scrape, and apply red high temp RTV. Then hopefully the P/s will work attached like the old one and not with hoses reversed. Thanks GSM
Thank you for your advice. It is very cold in the attic. Any suggestions on covering the system or keeping it warmer?
About all I can think of is open a supply run in the attic and close it when the weather warms a little.
GFM
I just ordered one on amazon . I made a ion furnace humidifier and i need to trigger the humidifier when the fan is blowing. The one that i have now with water curtain doesn't do how much i need. AIR IN canada is very dry. My hardwood floor shrink a lot. So i ordered a 10 head ultrasound humidifier with 48v power supply and i need to trigger it. So finally i found on amazon one with vacuum/low pressure trigger. I hope i can connect to 48v
Good
Thanks for the quick response GFM. Really appreciate it. Tried to find analog manometer locally. Only had expensive (few hundred) digital. Will look online. Meanwhile I'll do a cleaning. I don't understand collector hood (pressure) L- shaped setup top of boiler. Collector hood (pressure port) 90 degree turn to transition (suction port) then blower and vent pipe. Blew air into transition port clear. Collector hood pressure port cant blow into. P1 (-) to me means suction P2 (+) pressure. No?
Your information is extremely helpful to me. My Pressure switch was completely water logged, as were the hoses going into it. So I know from you video that water ruins the switch so I will replace it. Now I just need to figure out why it"s getting all that water in the hoses. Got any advise on that one ????
Yesterday a guy that works for me had his furnace start then shut the gas off repeatedly. I told him it was probably a sensor of some type. Now today mine is doing it. We are in the middle of what they are calling Winter Storm Goliath. Wind gusting to 55 miles an hour, My light blinked 3 times and the label said Pressure switch open or shut when it should be the other. I put 2 and 2 together and figured that since both of ours are doing the exact same thing and the high wind is probably blowing down the flue tripping the switch. Thanks for the video.
+waldan1701 That could very well be.
GFM
waldan1701
Welcome
GFM
You should be teaching in my college.
Its not better or worse. Just another way to look at it. Thanks for the comment.
GFM
He should definitely teach in a college or trade school. Half those clowns only know how to read a book and don't really know hands on!
@@AffordableHeating I guess I got very lucky, I'm in school now at my local college and just about every teacher owns a business, the program director is the go-to guy for the local business, recruiting wise.
I have a customer who had a house plumbing leak. The plenum insulation above the gas furnace got wet but I can't find any water contact to the furnace controls, wiring or internals. What visual indicators do you use to verify for water contact? I'm using ; signs of corrosion, water hardness minerals, streaking as well as wetted or matted dust or cobwebs.
You have done about all you can do visually. I would shut down the gas to the appliance and be sure the furnace shuts down on flame failure.
GFM
Its good to win.
GFM
Very informative. I was recently looking for a reason why my Ducane CMPE series furnace would shut off before T-stat temp was achieved. Sometimes it would fall behind 15˚ or more in really cold weather. While checking the pressure switch hoses, I found that little gray piece (you said reduced pulsations from the inducer) backwards up by the t bar where the hose splits off to the inducer and burner box. Only thing I can figure, someone yanked the hose off who knows when, little gray piece came with it, then the person put the hose back in place the other way around. I removed it because I thought it shouldn't be there. Do you think damage to the pressure switch could have ocurred? Should I put it back? BTW, the furnace has been staying on longer but keeping the filter door open a few inches helps too.
Are you sure you have a pressure problem? If opening the return air reduces the problem, I would be looking at return air restrictions (is the filter clean). Also the secondary heat exchanger could be plugged. Check this video: ua-cam.com/video/jjHR9GLvQ7g/v-deo.html I would not leave the pulse eliminator out. Hope this helps.
GFM
Great video. My mothers gas furnace has been not starting lately. It's about 12-13 years old in a modular home. It's upstairs and down draft with a full basement under the home. I did a quick search online and seen posts about trying to tap the plastic pressure switch. I've done that and then the furnace will start. Just a light tap with something plastic. I've been using a potato chip bag clip. Do these switches get sticky? Is 10-15 years about an expected life of these? We are in central,wi.
Your problem is either the pressure switch is failing (which is common) or the system vacuum is low. Causes could be vent blockage, dirty inducer wheel, inducer motor failing and possible tubing plugged. Hope this helps.
GFM
Help!.....I replaced the inducer motor on my York furnace and since then, it worked fairly well but seemed to be starting and stopping oddly at times...and two days ago the igniter went dark and inducer keeps going but no igniter and no gas and therefore no fire......replaced the igniter and still not working when I realized that the blinking red light was telling me that the pressure switch is stuck closed......what is my next step to check and could i have done something wrong while replacing the inducer?....did it exactly in reverse of what I did taking it off....love your videos..thanks
Probably your inducer replacement was ok. Check the sensing tube from the pressure switch for water or obstructions. Also look for vent obstructions or water in the vent of a 90% furnace.
i have a Rheem series 80 hot air furnace. recently it has started tripping the high level temp switch at 150 deg and then not resetting until it goes fully off and restarts. I have checked all the outlet registers and all the returns. if i open the door to the inline airlifted right before the blower the memo stays below 150 but if i close it it goes over. i do not understand how the airflow has reduced just recently or if the flame is putting out more heat. Also i see a replacement limit switch that has a high level setting of 160 instead of 150. i think that would solve the problem but would it cause any overheating? theater choice is to just leave the filter door open. any ideas?
+Peter McGroddy The Rheem furnaces have their limits wired so if they open, the unit must be restarted. Do no increase the temp of the limit. Dangerous. Look for dirty blower wheel, or blockages of the return air. Hope this helps.
GFM
my pressure switch issue starts on a reheat cycle but if you turn off the heat setting on the control board let the cycle stop then turn the heat setting back on it will take off and run but again when it tries to come back on again after it has ran it shows a pressure switch issue. any thoughts?
+wyomings alcoholic When you turned it off you rebooted it. Look for blocked tubing, vent blockages or failed pressure switch. Hope this helps.
GFM
I have a 6 year old Lennox furnace. Runs great until temps start to get under 0. Furnace kicks on and then after about 10 min goes into high fire. After running on high for 10min or so the inducer fan starts to pick up rpms. The rpms gradually go higher and higher until a pressure switch failed open code starts to flash and then the furnace restarts in low. It does this cycle non stop, high-low high-low. When it’s this cold it won’t keep up seeing as it needs to be on high longer. I cleaned the trap, had every hose off checking for clogs, took the inducer off and inspected it as well as checked the ports behind the inducer for and blockages. Everything looks fine. I’ve paid 2 different repair companies to come look at it and all they do is the exact same things I’ve already done and then tell me everything looks good. Also tried swapping the switch, no change. I have no idea what else to do!
Also after awhile the furnace will occasionally shut down and not start up and just flash the pressure switch open code. When this happens I noticed that if I take the hoses off of the switch and suck through them the red hose will have a tiny little water pocket in it. Not sure why, seems like condensation is getting produces in the hose, even though nothing appears to be plugged or backed up. Any help would be appreciated!
Check the end of the drain line outside. It is most likely freezing up.
Hi, could you tell me if Supco's furnace pressure sensor NS2-0000-31 can replace Honeywell's IS20146-3352? Thank you very much for the help!
The Supco product is a general replacement switch. The Honeywell is an OEM replacement. If the application is a gas appliance, you will need to use the OEM product.
This is not just an anti DIY opinion. These switches are very specific in their opening, closing and differential pressures.
GFM
I have an old sears gas heater , the blower keeps shutting off after about 45 seconds but flame stAys running how do i fix this issue
The blower should be controlled by a heat operated fan switch. You can separate the on and off temps farther and it will probably stay on for the complete cycle.
GFM
i have a lennox furnace i had to replace the control board and it was comming on for about 5 or10 sec than shuting down and will do that over and over so i replaced fhe flame sensor and it still does it can you please tell me what to check for now
The factor you need to look at here is whether the flame is on for the trial for ignition. The burner should stay on for a consistent time. Trial time can be from 4 to 7 seconds but should be the same every time. If so, it is a flame sense problem. If the flame is covering the flame rod completely and all wiring is tight including the ground wire to the chassis, then you have a control board problem.
If it is inconsistent or lasts longer than the trial for ignition, it is probably a pressure problem. You can temporarily jumper the pressure switch (only jump after the inducer comes on) and see if it continues. Let me know what you find.
GFM
My water heater keeps turning itself off and showing an error code--the vacation light and B and C lights are come on, and at that point, the hottest the water gets is about 70-80. It only happens from June to October. This is the third year. I thought it was the Intellivent computer, but the AOSmith says it is the air pressure switch located on the blower motor. Is this replaceable? One plumber just wants to replace the whole tank (11 years old), but that seems wasteful. What do you think?
First, I would be sure that the blower wheel is clean and the vent is clear. Many of the water heater manufacturers do not want the pressure switch replaced. They want the entire blower assembly replaced. Hope this helps.
GFM
Blower motors will often fail if wet. There is no certainty there. If you are set on keeping the furnace, you might try replacing the blower motor.
GFM
Hello Gary, Thank you for the video, I have AO Smith 40 gallons Water Heater and It is 2 years old unit. Today I have noticed that it did not work and i was able to get the codes from flashing light, It blinked 3 times which translates to Pressure switch, I called my plumbing heat supplier and gave him the part number and he mentioned that this switch is adjustable and I could not figure out how to adjust since there is not adjustment. Please if you can point me int right direction.
Thank you,
Rav
Do not, under any circumstances adjust that switch. The adjustment is probably sealed for just that reason. First, check the blower wheel for dirt. A clean wheel may just fix it.
GFM
Again great vids...!!!! I had my pressure switch changed exactly 1 yr ago because water reached into it (according to tech). What what cause water to reach into the switch. Blocked tube?
2 possibilities I can see. Unit is in an unconditioned space. The other problem may be the pressure switch has a small hole that tends to push any water back up the tube. If the hole is clogged, it could get water in it.
GFM
@@grayfurnaceman Condensing furnace-clogged drain. Water going from inducer to the switch.
@@123K4x4 I would replace the switch if it has had water in it.
GFM
If the furnace was wet, the manufacturer says pitch it. If you have insurance, they should pay for it. The blower motor has probably failed. When they get wet, you never know if they are damaged or not. In any case, the bearings will probably have reduced life. Hope it helps.
GFM
Question... I was on a call tonight where I had a pressure switch code. I checked all other reasons for a pressure switch failing. I had sufficient draft but contacts would not close. When I sucked on the hose the contacts closed. I jumped out the pressure switch and the unit fired. I was not set on the pressure switch had failed. Is there anything I was missin?
Can you do a video on a differential pressure switch?
I think that meter is made under a number of different names so you should be ok. The rest sounds like a plan.
GFM
I would be looking for blockages in the vent or manifolding on top of the boiler. The highest vacuum should be closest to the inducer. The switch is biased (means a spring on 1 side of the diaphragm will not allow switching if pressure is same on both sides). So it could work if hoses are backwards. Do not leave that way! P1&2 are probably factory markings. Again, venting block, inducer not up to speed, wheel coming apart etc. Vac gauge will help a lot.
GFM
I was going to check the heat exchanger when I started the unit today and STILL felt air coming from around the sheet metal plate with the motor/blower wheel attached to it. Maybe I didn't use enough although it looks sealed. I checked the cast blower housing for cracks and I don't see any. I used Imperial Red High Temp silicone sealant. Maybe you have to glop it on. Not sure.
Fantastic videos GF. I can tell you are a teacher. I looked through videos for answer to problem. Closest was How P/s on 398aaw Carrier is wired. Have Weil McLain Series 3 HE-5 with WR ignition. 3-terminal P/s. Old style was metal, new one plastic.Tried new one. Won't switch from NC to NO position. Front port of old P/s went to side of transition (suction). Rear port went to Front of Collector Hood (pressure). New one only works if hoses Reversed. Is that possible? What are P1(+), P2(-) on P/s?
Very informative videos! Thank you so much. Question: I've searched the net far and wide for a pressure switch on York Furnace P2UHD20n12001A. Current part shows a MPL-9300-0.65-DEACT pressure switch with 3-wire and 1-tube input. Any good leads on where I might find this part?
Larry Wolfe Hi, I am also having a problem with my furnace and am looking for that same switch. Were you able to find it? If not, how did you end up fixing the issue? Thanks
Desi Munda ebay sell one but we ended up going with a furnace repair mechanic. He called york who advised this particular furnace's original temperature switch was too low and suggested a higher temp limit switch. That apparently was problem.
I also have a York System and replaced the pressure switches and circuit board. I keep getting the signal telling me the pressure switch is stuck closed. I blow in the sensing tube for any moisture and then restart the system. It works about 70% of the time but a pain to keep going up to the attic to have the system run. Any ideas? Could the new swtiches be bad alreay (about 1 year old but first winter) Any advice would be great...
Is the system in a unconditioned space? (like above the insulation). If it is quite cold there, some furnaces were not designed to be below 50 degreesF. Other problems could be blocked vent pipe(90% furnace), inducer wheel dirty, heat exchanger cracked (CO hazard), or inducer motor not coming up to speed. Hope this helps.
GFM
I would start at the induce outlet.
GFM
My heater has a presure switch how dp
I hope I don't have to pitch it. It is like 2 years old and my deductible is $1000. The burners and everything didn't get any moisture on it just the lower circuit board and the bottom of the blower. Do you think its the blower? I already replaced the board that got wet. I tried putting direct power to the blower from a ext cord and got nothing.
Thanks excellent video. Can you tell me with condensing furnaces, why would there be water in the pressure tube from the inducer? What is that a sign of exactly? Thanks again, very informative
Aaron Wilmoth Several possibilities here Low spots in the tubing will sometimes collect water. If the furnace is installed in a space that is below 55 degrees or the return air is that low. Also pressure switches sometimes have a small hole in the diaphragm to bleed a small amount of air into the switch to keep it clear of water. Hope this helps.
GFM
Thanks for your help! Awesome!
grayfurnaceman My furnace, a Lennox G61MPV, had that exact problem. The tubing that runs to the pressure switches was too long and drooped below the openings where water collected and caused faults. Is that tubing installed before the furnaces are shipped, or do the installers put them in? It seems like either should have known better.
My house is not even a year old and today I got the light indicates a stuck open pressure switch. So I tapped on it lightly with marker and the furnace is working. Can our series of negative temperatures cause this? Was it defective from the factory?
It is probably under warranty. The low temps should not cause this. Hope this helps.
GFM
Good evening GFM,
I have been freezing for several days and am glad to watch your videos! You mentioned in one of them "if you unhook the hose from the burner box and it fire up" then that is the problem. Our furnace fires up perfectly if I disconnect that hose - so does that indicate that my pressure switch is the culprit and needs replaced? I appreciate your direction!
Kris Brower Look for blockages in the combustion air piping an also in the vent pipe. Also check the condensate drain for blockages.
GFM
If I tap on the switch it will activate, it is intermittent. If I hold it with the wires upward it makes connection every time I try that. If I hold it with the wires facing downward and the adjustment allen up it shuts of the gas valves. Normal operation or bad switch?
Furnace shuts off after the fan kicks on, or doesn't ignite unless I tap on the switch while it is vertical.
The switches are quite picky and some are position sensitive. You could have a switch failing or a venting problem. I would replace the switch first.
GFM
I have water puddling behind my unducer above the blower fan on the top half of a concord 90% efficiency furnace my drain lines are clear any insight would be great thanks
You probably have a leak where the inducer mounts to the manifold of the secondary heat exchanger or in the manifold itself.
GFM
On a Coleman mobile home furnace/80%-er, the dual-port differential pressure switch spec shows on the label only as 0.10" WC. Coleman Tech Support once told me this was the "set point," and it would take approx. 0.20" wc to close the switch. If this Tech's statement was correct, please define "set point."
+JustPlumDucky Interesting. There is a differential on all pressure switches. He probably means that at .20 it will close and at .10 it will open. Sounds like a good subject for a video.
GFM
Gray what Manometer would you reccommend for an HVAC tech, Im looking to buy one and only one and would like to go higher quality rather than poorer. What brand or model would you reccommend for someone in the trades??
I have a Nordyne M1M Series. We keep getting blinking red light that pressure switch is open. We replaced it and still get blinking red light. We live 80 miles from town so technical repair is not possible. Took off blower assembly and cleaned it out. Still blinking light. Any suggestions?
We had a repair company come out the other day and they told my wife the pressure switch had failed the pinch test and that the unit kept running. Is this pinch test for real? Thank you for your video!
Mark Kramer Sorry for the wait, I have been out of town. It depends on what furnace you have. If your furnace is over 25 years old, it may have value. Any furnace with an integrated furnace control (control board) and some others, the furnace control checks the pressure switch operation with each cycle. Hope this helps.
GFM
Thanks for your reply!
Well I've watched and read your entire site for heating and armed with that knowledge and some gear I just bought I fired up the furnace waited for it to start circulating air and pulled the vacuum line to the pressure switch and it shut down the burners instantly. I then reattached it and after a short wait the burners reignited. I tried this "pinch test" and could not squeeze the vacuum line hard enough to get the furnace to shut down. So I'd be wary of techs using this test to sell you a $280 switch that you don't need.
I then hooked up a manometer and measured .7" WC. It should have been .5" but I haven't read anything about the value being higher than it should be so I'll keep looking around. I'm thinking the variance may be due to how I had to adapt hose sizes. The Fieldpiece manometer has this non removable barbed fitting on it. It's probably the next size down from what I needed to fit in the line that goes between the pressure switch and the combustion chamber. So I have one diameter line for about 3 inches hooked to that non removable fitting. Then they gave me a double ended barbed adapter to get up to the proper size line. I used that then hooked up the proper sized line then I have that going to a T fitting so that the manometer sits in line between the pressure switch and the combustion chamber. So maybe the smaller diameter line and all these adapters are messing with the reading.
This was a lot of fun learning about all this. I'm going to read all your AC stuff next as it's supposed to be 96 today and I don't want to get taken on the next service call.
Thanks for sharing, very informative. Are these (Or could they be) used to disconnect an electric source? For instance, with a HHO generator: An HHO generator (from my ,hobbyist, understanding ) uses electrical current (battery) to separate HHO into Hydrogen (the fuel) and Oxygen. Of course I understand it's a little more complex than that, Lol just figured you'd know what I meant. Do these disconnect the electrical flow when the gaseous pressure exceeds, or drops below, the water-table range dictated by the pressure switch? Just checking as I'm only vaguely familiar with gas systems.
The pressure switch works with generally negative pressures in the fractional water column range. They are capable of switching 24 volt in the fractional amperage range.
GFM
:) Thank you.
My inducer blows never shuts off. The furnace works ok (heats normally) in regards to the thermostat, but blower never stops running. The vent pipe is shared with water heater (gas) Tempstar furnace. Thanks
Hello. My furnace shutts off. Code shows pressure switch issue. Replacing didn't fix it. By removing front door it's runs ok.
Question. Can we replace new pressure switch with lower rating
Absolutely not on the pressure switch change. Check vent and combustion air inlet for blockages.
GFM
Do I have to buy the same exact manufactor or can I interchange it with the same wc ???
Factory or factory authorized pressure switch only!
GFM
Tempstar NUG5100BHB1 The Inducer/Cumbustion blower (fan on vent pipe) never shuts off. The furnace does heat ok, according to the thermostat. The gas valve opens, burners ignite & shuts off when house temp raise to themostat settings. The only way to turn OFF this blower/fan is to turn off the circuit breaker. The furnace wwas installed (new) 1995. I heat up the house & manually turn off the furnace by the breaker. I just noticed this problem yesterday. Thanks
Are pressure switches always is the vertical position because of the diaphragm?
There are multiple positions for pressure switches. The switch may have an indicator on it that gives its proper position.
GFM
It sounds like what gray is saying jeff, that your control board is "Stuck" sending power to the inducer id grab the model number off your board and replace it.
Hi GFM. Wanted to follow-up. Called Propane Company's Service Dept. Tech threw parts at it (I had them all in stock) until it worked said other things wrong??. In the end he reversed the hoses on the P/s and boiler is back in business $380 in labor later.
Meanwhile, GSI manometer equivalent (Pyle PDMM01) arrived. Want to test it. Saw your video on the GSI. One question. Two ports on top of unit not labeled. Which is Pressure and which is Suction port? Thanks. John
Actually they seem to both be negative. Both lines are on the negative side of the inducer. The collector fitting sometimes has a very small orifice to lower pulses from inducer. A small wire may clear it and get you back in business. Check Amazon GSI brand for meter. Hope this helps.
GFM
Can you wire a pressure switch backwards? Reverse the polarity?
If it's single pole single throw, yes. If it's a single pole double throw, no.
GFM
I have a carrier unit that's giving me a pressure switch code but it will fire up code stops and run for about 4 days before it shut off
Could be a number of problems. Blocked drain, water in the vent, ice on the termination, water in the pressure line, heat exchanger failure, inducer failing or failed pressure switch.
GFM
I found that screw in the pressure switch and thought to myself who put that screw in there. Seems like my pressure switch must be working but furnace keeps turning off....I then go downstairs lift and drain the Condensation hose of water turn the furnace back on and it works until..... the hose fills with water again. Did the Vacuum Condensation hose out .....So I am thinking I have to replace the Condensate pump ? Ducane Furnance.
Sounds like the condensate is blocked.
GFM
I have Vacuumed the line from the Pee Trap to the floor drain..... but everytime the line from the pee trap to floor drain has water in it again the furnace stops ???
I would check all the condensate lines for blockages.
GFM
Well did the vacuum thing again and it's been working again so I don't think it's the pressure switch. But the pee trap has 3 hoses going to it one from the pressure switch, one to the intake or exhaust ? And the other to ( ).
Still holding at 21 ...... since my post ( a week ago) Happy New Year
mr GFM.. Hi.. i'm currently in technical school to become an HVAC/R technician! Can you please shed some light on the industry and point me in a direction to go, for when i'm out? Theres so much to learn, and it all seems fairly daunting! I've heard I must be an apprentice to a plumber for four years before I can do gas furnaces? Any tips you could give would be more than welcome bud..
In Canada you do not have to do any Plumbers courses or Plumber Apprenticeship to be a Gas Tech and work on Furnaces or any other Gas fired appliance, up to and including 400, 000 BTUH. You need to do your trade school and apprenticeship first for a G3 Gas Technician License then go for a G2 or G1 Gas Tech
license