room thermostat Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[Bob Smith]

I am replacing an old Suntine ? room thermostat which is wired to the CH boiler controller with earth, neutral, live, and one other wire. I have purchased a new digital unit which has only 3 connections, normally open, normally closed, and common. Can anyone guide me as to how to connect the new unit?

[plumbbob]

New digital thermostats unlike the old mechanical stats do not need the neutral. The neutral was connected to a ballast resistor and used to increase accuracy.

Just connect the live to common and the "other" wire to normally closed.

Make sure you have definitely identified the neutral or there will be a bang! Don't assume simply by colours.