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Ben Blaukopf[_2_] Ben Blaukopf[_2_] is offline
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Default Central heating won't turn off

On Nov 21, 4:11*pm, "Simon T" wrote:
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?


The valves might be closing mechanically, but not electrically - the
resistance across brown/orange should be infinite (i.e. open circuit)
when the valve is closed. That still shouldn't cause the pump to run
though, without some other problem!

Take a look he

http://wiki.diyfaq.org.uk/index.php?...s_and_Zonin g

And get a multimeter out and start seeing where reality diverges from
what you expect.




However, even if the valve is faulty, if the timer is off then the
pump should still be off, so you either have a wiring fault or a timer
which is lying to you.

I would start by