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My thermostat operates but seems to be badly calibrated. It will hold temperature, and you can adjust that temperature, but its not the temperature it says on the dial! It goes much higher than the stated number.

For example: to get the room to 70 F, you have to set it to about 55. To keep the nighttime temp. colder around 55, you have to turn it to around 40-45 but not as far as "off". As you turn it there are some audible clicks of either the mechanism or relay as it switches on/off (I think that's what I'm hearing).

It is a 240V line-voltage thermostat that controls an electric baseboard heater.

Under the cover there are two screws (allen key I think) which I imagine might be used to calibrate the mechanism. I asked the manufacturer and they said they don't have any manuals for this 20-30 year old model.

I could just experiment but thought it was better to ask here first rather than risk making it worse... but I'll do that if I can't find any other information.


The top photo was taken when I set it back from 70 (which it overshot) to a nighttime temp.

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  • "for this 20-30 year old model". Yeah, I think it is time to put this one to rest and buy a new one. – Gunner Jan 28 at 12:12
  • @Gunner which I'll do if I need to. But since it has (apparent) adjustments that seemed worth trying first. – UuDdLrLrSs Jan 28 at 12:25
  • I'd experiment with it. Many questions and problems on this site are about new thermostats that don't work at all. – JACK Jan 28 at 12:58
  • @JACK that's probably a good idea, but I was hoping at least for a theory of what the two screws do before I just randomly start making changes. In part this is because its going to be a long process to test it since I'll have to wait for the room temp to rise/fall. – UuDdLrLrSs Jan 28 at 13:19
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    The knob turns a threaded spindle that changes the preload applied to the bimetallic element - which is usually a dark blueish color with printing on it just like that plate, though they're not usually formed into shapes apart from the slight dishing that causes them to flip from one curvature to the other at the set point. Anyway, have you pulled the knob off? It might be just a matter of repositioning the knob. – Phil G Jan 28 at 16:30

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