Roger Mills wrote:
In an earlier contribution to this discussion,
The Medway Handyman wrote:

What's the +/- tolerance on a bog standard wall thermostat?

I mean, if you set it to 20c will it trigger on at 19c & off at 21c?

Are you sure that you mean tolerance - 'cos what you've described is
hysteresis.

I mean hysteresis now I know the correct term :-)

If by 'bog standard' you mean a mechanical by-metallic
stat, that will inevitably have a difference of several degrees
between the switch on and switch off points.

Thats what I was after knowing - thanks.

As someone else has
said, these often have a built-in accelerator heater. This is a small
resistor which is powered when the stat is 'on' and warms up the
innards so that the stat switches off slightly before the target room
temperature is reached. Of course, the rads don't cool immediately,
so the room goes on getting hot for a bit - so the accelerator heater
just helps to reduce overshoot.

Didn't know that.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk