On Sun, 04 Mar 2012 15:21:19 -0000, DerekG wrote:

On Sun, 04 Mar 2012 14:42:26 +0000, Lieutenant Scott wrote:

Can someone explain the use of a heater INSIDE a mechanical (bimetal
strip) room thermostat? (It usually just seems to be a resistor placed
near the bi-metallic strip).

All it seems to do for me is make the thermostat very inaccurate.

[ ... ]


I've replaced the offending pile of crap with a digital one anyway, but
I wanted to know why they design them like this.

It's an anticipator, and should be set so as to introduce exactly the
right amount of heat inside the thermostat casing so that it doesn't have
to wait for the heat to percolate from a radiator across the other side
of the room, thereby tailoring the response so that it stabilises sooner.

It's a bit like trying to throw a Yo-Yo away whilst still holding onto
the string. And yes it's a crap plumbers idea.

DerekG

I've found that the convection of the room air from the heat source (a radiator) heats the room very evenly anyway. The stat switches off when the room reaches the required temperature without that bloody heating thingy!

As you said, it just doesn't work as designed - it's guessing! All that happens is when the heating is needed to be on more, it thinks it's going to be warmer than it is, so it doesn't switch it on enough.

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