CH problem

[Bob Eager]

We seem to have a little problem.

CH is gas boiler (Potterton Netaheat), programmer has separately selectable HW and CH times, and they are independent of each other. System has pump, cylinder etc. remote from boiler, thermostat in hallway.

Problem: the CH comes on even if thermostat is set to minimum. I then turned the CH off completely at the programmer (in other words, disabling the timer) and STILL the rads get hot. However, if I turn the HW off at the programmer too, the rads cool down.

Now, this isn't my area at all, but I would suspect either the programmer or the electrically operated valve (presumably a 3-way one since we have independent control of CH and HW). I can't actually look at the valve right now because it's in a room where SWMBO is asleep after a bad night!

Are my assumptions correct? And is the valve the most likely culprit? If I read the FAQ right, the most common failure mode is a burn out coil leading to CH on all the time - is this correct?

[SteveS]

Not my field either, but I have experienced the same problem. In my case it was the valve actuator, a Drayton. It appears to have a synchronous motor and various gears and microswitches made of polycrackathene and crapite. The gears had worn and were slipping. You may find that the valve has a lever with which you can disengage the valve from the actuator and set the position manually, You could try manually exercising the valve just in case it's got sticky, and also verify that the system works correctly with the valve position manually set. I'm quite possibly wrong, but I think that the valve actuators are widely available as separate items. Just make sure you make a detailed diagram of which wire goes where when you remove the old one.

HTH, Steve S

[Andy Hall]

OK....... Of course we're all dying to know why, but are too polite to ask.

Either a burnt out motor or sticky valve or gooed up with grot.

You can take the head off of the valve and check whether or not the motor runs (you can buy the motors separately). Then test the valve base, trying to turn it. If stiff, your culprit is there. It could be a microswitch in the valve head, but less likely. That needs a test meter to check out.

.andy

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[Bob Eager]

Small boy with nosebleeds!

Thanks....that was what I was thinking. Test meter no problem - have several!

[Andy Hall]

Oh dear. If it's persistent, try Vaseline to keep the area moist, otherwise it's ENT visit with silver nitrate on a stick. Sounds worse than it is, but all a bit upsetting for a small child.

I have that T-shirt......

Obviously if the valve does seem sticky, this is a good time to check out the system thoroughly, by draining, flushing etc. I've posted a method of how to do this a few times.

.andy

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[Bob Eager]

Hmm. Further examination indicates that, even with the CH part turned off at the programmer, water flows out of both ports of the 3 way valve. As might be expected given the symptoms.

HOWEVER....the CH pump is also running....! Surely that would indicate a fault in the control system rather than the valve - or have I missed something?

[SteveS]

Probably not a fault in the control system. Our system (like many, I suspect) uses pump for both HW and CH.

You may have a relay box into with the wire from the valve actuator disappear. You could try listening for the relay clicks as you turn on and off HW and CH (various combinations). If there are relays in there you could also try cleaning the contacts and checking the coil continuity, after first isolating the mains supply.

Steve S

[Bob Eager]

Ours doesn't. The pump is on the downstream side of the CH port of the 3 way valve. I should have made that clear. Looks like it's to assist CH circulation, but cylinder is gravity fed.

Thanks...will investigate further but still wonder about that running pump.

[SteveS]

Could still mean that the valve actuator is at fault. My guess is that the pump will not turn off until the valve is actually at the HW only position, as determined by the microswitches in the actuator.

Steve S

[Bob Eager]

Aha. Good point...!