The Natural Philosopher wrote:
ARWadsworth wrote:
Roger Mills wrote:
On 21/11/2011 16:11, 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? Any suggestions what to try next?

Thanks in advance.


Each of the zone valves has an auxiliary switch which closes when
the valve is open, and is independent of the motor circuit. These
switches on the two valves are wired in parallel - with a permanent
live feed on the grey wires and a switched live (which switches on
the boiler and pump) on the orange wires.

It's almost certain that one of these switches is stuck in the
closed position - even when its valve is closed. If you disconnect
the valves' grey and orange wires from the junction box, and check
for continuity, I think you'll find the problem - one or other
switch is stuck shut.

That is the most likely answer.

I went to a job this evening and I just disconnected the orange
cables in turn to identify the faulty 2 port valve.

if you are lucky, you can get just the switch.

Otherwise its a new head job..takes 5 minutes to swap out - no
plumbing required :-)

I am not going to mess about swapping the switch at work. The customer was
given a price for a new head (Drayton so it's an easy swap). It's a balance
between labour and parts cost and I have to put the customer first.


--
Adam

* Sometimes I like to lay in my neighbours garden and pretend to be a
carrot *