the central heating comes on even when the timer is on off. The timer is a siemans rwb7 which was recently fitted replacing rwb100 thinking it was a faulty timer. The timer switches the heating on but boiler keeps working switching on an off even after the timer has gone past the off trip.

mike juhasz, October 2008

Not certain think the switching is should be volt free
check that room stat cable is not close to a mains supply as current induced can affect a volt free supply

a, October 2008