Leaving the thermostat programmer on 'On'

[adamt11]

Does leaving it on the ON setting use energy if the wall thermostat is turned down and the radiators are off?

 

[Rodders53]

It will depend on the make and model of the device(s) most probably.

Read the manuals it might tell you.

If it has a clock programmer or is a wireless receiver it will use some energy.
Not a lot typically, like most stuff in standby.