In article
,
Sansui Samari wrote:
Certainly in the UK it's a form of mechanical switch. It can carry
mains or low voltage AC or DC - not really possible with a solid state
device. My guess is it may be piezo operated. But that's only a guess.
Mine is rather louder than a relay.


There are solid state relays that will supply fairly high current at
240vac with a 24vdc switching voltage. They are very common on
automated machinery, I'm not sure if they would be used in a
thermostat, the ones we use are pretty spendy.

Thing is in the UK it was pretty common to have mains to a mechanical
thermostat. Which also supplied an accelerator coil round the bi-metallic
strip to improve accuracy. So aftermarket types can all handle this. On my
last system here everything electrical was mains - gas valve, pump, three
way valve, room stat and water stat. A very simple system which worked
well for years. I've replaced the boiler with a condensing type which has
electronics so has to have a low volt supply for that. But uses sensors
instead of thermostats for house and water temperature which is now set
via the programmer, rather than locally.

Aftermarket thermostats will most often be fitted to older systems here -
so have to cope with either AC mains, or low volt AC or DC. Which I'd
guess rules out a solid state switch.

But even a solid state switch will take some current when made - does it
not? So not ideal for battery operation.

The programmable thermostat I retro-fitted to the old system - allowed you
to set different temperatures for parts of the day and days of the week -
used four AAs for everything - no power from the line - and they lasted
about 2 years. They are a very worthwhile addition to an older system.

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*Also too, never, ever use repetitive redundancies *

Dave Plowman London SW
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