Room thermostat problem

fixitflav · Nov 20, 2017

A friend has a Honeywell T6360 roomstat. On turning the knob to say 20°C to call for heat, heating starts but doesn't satisfy the stat till way too high, at least 25°C. I found the neutral to the accelerator hadn't been connected, wired that up and expected a cure, but not noticeably better. I checked the resistance of the accelerator, about 330000 ohm, which means it outputs < 0.2 watt. Gut feeling is that's too low. Anybody know what the resistance should be, or any other comments? Appreciate any help.

Harvest Fields · Nov 20, 2017

Not off the top of my head. But it is not Unusal for these type of stats to lose calibration over the years. Where is the stat located. How far away is the radiator in the same room. Is the radiator switched on?

fixitflav · Nov 21, 2017

Harvest Fields said:
Not off the top of my head. But it is not Unusal for these type of stats to lose calibration over the years. Where is the stat located. How far away is the radiator in the same room. Is the radiator switched on?

It's a replacement stat, about 2 years old, and never been right. I think he broke the previous one, which was OK till then, so it does seem to be this stat. I've heard a suggestion the differential might be adjustable. It doesn't mention that in the data sheet but you wouldn't expect it to. I'll give it a go.
Thanks anyway

Ric2013 · Nov 21, 2017

Crude things those stats. You could remove the faceplate and pull the knob off and put it back at a 5°C higher setting, hopefully bringing the stat back into reasonable calibration. You can on some Honeywells, anyway.
The older brown and taupe Honeywell stats had less hysterisis in my limited experience.

fixitflav · Nov 21, 2017

Ric2013 said:
Crude things those stats. You could remove the faceplate and pull the knob off and put it back at a 5°C higher setting, hopefully bringing the stat back into reasonable calibration. You can on some Honeywells, anyway.
The older brown and taupe Honeywell stats had less hysterisis in my limited experience.

OK but it's the hysteresis that's the problem, not calibration. Agree about the older ones, I had a Honeywell T403A, installed in 1973 and still OK. This has a bimetallic coil, no accelerator, the contacts magnetic to give a snap action and prevent dithering. Differential fine.