In message , Simon T
writes
OK, I know other people have had this problem and have done a cursory
Google search, but have not been able to shed much light on what might
be the problem in my particular case.

Basically, the central heating round at my parents house refuses to
switch off, even when the thermostats aren't calling for heat and the
timer is off. The pump continues to run and the boiler continues to
heat the water and the only way to get it to switch off is to turn
everything off at the mains.

I suspected it might have been a stuck 2-port valve, but having checked
both of these found that neither one (CH or DHW) were stuck and
appeared to be operating fine.

Their set up is a standard Gravity Fed System with the feed and
expansion tank in the loft.
Glow Worm hideaway boiler (in a small room next to the kitchen)
Danfoss Electronic Timer (in the kitchen)
Danfoss Room Thermostat (in the Hall)
2x Danfoss 2-port valves (for CH & DHW - in Airing cupboard next to hot
water cylinder)
Danfoss cylinder stat (in airing cupboard)
CH pump (unsure of make - in the airing cupboard)

Again, the 2-port valves were most definitely not jammed open, which
was my first guess. In fact when I went round there to check them, I
found my mother had switched the gas off on the boiler (it didn't occur
to her to switch off the power supply), the timer was off, both 2-port
valves were closed, but the pump was still running?

What do you mean by "thermostats"?

What resistance is the temperature sensor showing at the pcb connector?



--
geoff