Honeywell oldie thermostat

JennyLaslo · Saturday at 7:05 PM

No matter where I put this dial, the radiator is always on unless it's under 10. It feels more like a level control than a thermostat detecting and regulating radiators on and off.
It is 41 years old now, would this suggest the thermostat is off (to a high degree not just a few c)?
Thanks

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Deluks · Saturday at 7:16 PM

It doesn't work in isolation, what other controls do you have?

CountryFan · Saturday at 8:49 PM

It could be out of range, but could also be a different control as above

JennyLaslo · Sunday at 5:51 PM

The other controls I have are an old randall 103 timer in the kitchen across the hallway from the Honeywell. Other than that all I can see are radiators and the heat only boiler in the garage

CountryFan · Sunday at 7:53 PM

JennyLaslo said:
The other controls I have are an old randall 103 timer in the kitchen across the hallway from the Honeywell. Other than that all I can see are radiators and the heat only boiler in the garage

No motorised valves then?

ericmark · Sunday at 8:16 PM

I note this thread about same thermostat.

there is normally a diagram inside the thermostat, note wires numbered 1, 4, 3, 2, 5, so linking 1 and 3 should make the boiler run.

stem · 2026-01-12T15:06:37+0000

Seen this a few times over the years. These old mechanical thermostats have a bi-metallic component with two dissimilar metals fixed together that expand at different rates so that it moves to open and close an electrical switch. They rely on the temperature change to bend the bi-metallic element, but the movement is tiny, so wear over time can result in a small physical move which would in reality require a big temperature change to achieve, so switching at 10C instead of 20C is not unrealistic.

Once your room is at the temperature you require, try tuning the thermostat dial down very slowly until the point where it clicks 'off'. Sometimes the thermostat will continue to work and turn the heating back on as the room cools, and if it does you can continue to use it but with a recalibrated setting.

Hugh Jaleak · 2026-01-12T20:28:48+0000

CountryFan said:
No motorised valves then?

Going by the age of that Stat, I'd imagine the system is Gravity HW and Pumped CH, so all the Stat will do is switch the Pump on when CH is called for.

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Honeywell oldie thermostat

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