Heating and Hot Water Won't Turn Off

I received a phone call from a concerned customer because her boiler was running continuously and her hot water seemed to be exceedingly hot even though both the heating and hot water were turned off on the programmer.

A colleague of mine was in the local area and so he went round to check it out. Sure enough the boiler was still running when he arrived and the house was like a sauna. My colleague removed the programmer from it's baseplate and the boiler went off. Assuming that the problem was with the programmer he replaced it, tested the operation of the three-port valve and left as everything was working fine.

A couple of days later and I receive a phone call from the same lady because her heating and hot water won't turn off again. I went round straight away to find the boiler constantly running and the house like a sauna. The lady had turned the room thermostat right down and both the heating and the hot water off on the programmer.

I looked at the electrics and checked what voltage were where. There was 230 volts at the grey, 24 volts at the orange and on the white wire of the Drayton MA1 three-port valve the voltage exceeded the scale of my Fluke T3 Electrical Tester. It would seem that 24 volts is enough to power the switch live of the Worcester 15 Ri boiler which was fitted.

I disconnected the orange wire and hot water calling from the switch live to the boiler and the boiler went off.  The voltage was coming from the orange wire of the three port valve. I replaced the head on the motorised valve and re-tested the operation of the heating system, which has been working correctly for the past week.

Disclaimer: The works described in this blog are a record of work undertaken and should not be taken as guaranteed to solve your problem. Work should only be carried out by persons qualified and competent to do so.