On 09/11/2019 13:00, Graham. wrote:
mm0fmf Wrote in message:
On 08/11/2019 19:43, alan_m wrote:
I assume any battery run thermostat will have a relay for any mains
voltage switching.

Better, they have a latching relay. So power is only drawn from the
battery when turning the relay on or off. No power is needed to hold the
relay in either state.


If the thermostat or programmer is hard wired and switching mains,
surely it would be mains driven, and wouldn't need a battery
other than for power fail backup?


Most of these electronic room thermostats cater for a variety of
different configurations so may use battery for electronics and a
mechanical relay for switching.

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