Please take the time to view the documentation that Honeywell provides for the device customer.honeywell.com/resources/techlit/TechLitDocuments/95c-00000s/SD_IS_150.pdf and you will see that it explains that the mixer could fail due to hard water scale build-up. It also explains how to disassemble and clean those parts or you can buy a rebuild kit and replace the guts without removing the valve body. It also explains where the "secret" screw is. :-) If anyone does attempt the cleaning procedure, DON'T, unless you know what you are doing. It requires you to shut the boiler down to cool and turning the water supply off. It will require draining the water from the line or suffer a mess. It all depends on where installers placed cutoff valves.
I am wondering if you can remove the interior guts to trouble shoot?
Please take the time to view the documentation that Honeywell provides for the device customer.honeywell.com/resources/techlit/TechLitDocuments/95c-00000s/SD_IS_150.pdf and you will see that it explains that the mixer could fail due to hard water scale build-up. It also explains how to disassemble and clean those parts or you can buy a rebuild kit and replace the guts without removing the valve body. It also explains where the "secret" screw is. :-)
If anyone does attempt the cleaning procedure, DON'T, unless you know what you are doing. It requires you to shut the boiler down to cool and turning the water supply off. It will require draining the water from the line or suffer a mess. It all depends on where installers placed cutoff valves.
It's a bad design and these valves regularly seize up and cannot be turned, like the one in the video.
Mine is seized up and won’t turn. Anything I can do to loosen it up?
Its leaking!!! Crap show!