I have an oil burning boiler, hot water tank,programmer and a room stat .Been fine for past 7 years.Every so often the room stat with led (simple) will not turn off.Changed room stat .3 days later it happens again.Switch off supply to programmer and it works fine again.I can hear the stat click off but the led is still on and so is the boiler /pump.Wierd,.The stat only has 3 wires ,pos,demand, led. A 3 way valve and programmer .Any suggestions gratefully received.
