Room Stat Advice Needed.

[steptoe]

Right, just to add something to this,

I fitted a Salus stat today, not the same as the OP, but, it jogged my memory about a quirk some Salus stats have,

They are particular about the L and SW L connections,

Unlike most stats that don't really care what terminal the permanent live is in, Salus do,

May be an idea for the OP to check which terminal the live and switch live are in. 

 

[ProDave]

Are you SURE the neutral is connected?

If not the accelerator heater won't be powered and this will have the effect or raising the switching temperature, as well as introducing a lot of hysteresis between on and off temperature (which is the purpose of the heater)