Central heating won't turn off

Simon T · 2011-11-21T16:11:59+00:00

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?Any suggestions what to try next?Thanks in advance.