Heating Continues after programme ends

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I have a potterton 80e bolier and programmer single pump with HW and CH valves.

Problem boiler continues to heat radiators once programme ends. temperture can only be controlled at boiler Thermostat only way to close down boiler and close CH valve is to remove power at mains.

If room stat is selected to zero and programme starts boiler dose not run Select room stat to call for heat boiler runs. return stat to zero boiler continues to run.

I have noted with programmer off and room stat selected up for heat then the selection of advance on the programmer the boiler runs if advance selected again seconds afterwards boiler stops. If left to run control is lost again.

Don't have circuit diagram to understand whats not removing the live on the valve which I assume is being held upon so calling for heat!

Any trouble shooting types very welcome I dont think it the programmer you can remove the panel and still the boiler runs on.

HW performs correctly at all times
 
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Thank you for your reply.

Both valves run freely IE CH closes without delay when pwr removed.

Based on circuit diagrams provided the room Stat appears key in calling for heat. Should I try isolating this at the junction box and observing what happens?

Can room stats fail in such away as to cause such a hard fault?
 
Has it always functioned like this? or has something changed?

It could be incorrect wiring. For example, inside the motorised valve for the CH there is a microswitch with a permanent live supply. When the valve opens. This switch operates and turns on the boiler & pump.

Now if this switched live for the boiler is somehow connected back to the supply that opens the valve, once the valve has operated the switch, the valve will stay open no matter what you do with the programmer or thermostat. Turn off the power and you will loose the live to the microswitch which will allow the valve to close.

Turn the power back on, and it will remain closed unless the programmer & thermostat are turned on, then the process will be repeated. The valve will open and stay open until the power is removed.

If this sounds like what happens, check that the wiring for the CH motorised valve is not shorted across somewhere.
 
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As I write the system is performing normally! How & why I have no idea

Earlier this evening whilst the fault persisted I noted that at the Wiring Centre there was no Live at the room Stat terminals although the boiler was running. Which would suggest the Live had been lost from the Programmer? Would losing the live from here cause this or would it not be true to say that turning the Stat to zero would have the same affect?

I have checked the room stat and it function correctly as a stand alone item

Why the system is working (how long for?) I dont know but power has been off & On all evening trouble shooting.

I m now appear to be chasing my tail any ideas?

Thanks in advance
 
Intermitent stickin microswitch in one of your motorised valves take apart and WD 40 the switch
 
The micro S/W is mechanically depressed when the valve is opened. Not until the valve closes does this release the microswitch. This does not appear to be the problem
 
A sticking microswitch wouldn't cause the problem you describe anyway. The valve would close and stop the hot water flowing to the radiators, so they would cool, but if the switch was sticking the boiler would stay on. (Unless this is what you mean by "boiler continues to heat the radiators" in which case your description is not quite right) Also turning the power off would not release a sticking microswitch.

Don't worry about the wiring too much. Not everyone wires these things exactly the same, it varies usually according to the close proximity of the various components to each other and/or ease of wiring. Doesn't mean it's wrong. Sometimes the thermostat gets its supply directly from the programmer if its closer than the wiring centre. Anyway if it's working now it must be getting a supply from somewhere.
 
Help! The original problem which cleared itself with no change of units has been replaced by a more annoying problem.

Select CH on boiler runs system function correctly. Select HW boiler runs for a few seconds and then shuts down. Boiler will not relite, both HW and CH valves remain fully open pump and boiler stopped?????

Shut off HW reselect CH and system runs happily. Its driving me mad now so need a reply from someone who lives and breathes this sort of thing. I confirm again no item has been changed no wiring changes although this problem implys to me wiring

Help Christmas is coming Family are staying!! :cry:
 

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