I want to replace the wall thermostat with an up to date programmable version. The old one has connections to common-live and then the normally open and normally closed relay contacts of the thermostat. Are both of these contact connections needed for the boiler or will it work with just demand for heat connected?

Malc, January 2008

Thanks for the quick anwer. I have a honeywell V4073A mid position valve with connections
1) white - heating on
2) grey - hot water off
3) Orange - boiler and pump live
4) Blue - Neutral
5) Gr/Ye - Earth

Thanks,
Malc

Malc, January 2008

IT ALL DEPENDS ON THE TYPE OF VALVE YOU HAVE ON THE SYSTEM, IF ITS SPRING RETURN THEN YOU WILL ONLY NEED THE CALLING WIRE.

MIKE GASMAN, January 2008