In article , John
john.plant90@NO-SPAMntlworldDOTcom.? writes
I have one of the small square ones from Screwfix fitted at my daughter's
house.

Had a anguished call to say that the heating was stuck on and had reached 28
degrees.

Fiddled around and eventually swopped the batteries. It now works.

Was it due to the fiddling with all the settings - or do the contacts 'fail'
in the closed position if the batteries weaken?
The relays in these are latching (magnetically assisted I think) and so if
the batt fails when on demand then it won't have the oooomph to reset the
relay.

The Horstmann looks like a pattern match for a Tower one I have as a
temp solution and I don't hold that one in high regard.
--
fred