Boiler not controlled by programmer

29 Dec 2003
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United Kingdom
Recently the programmer seems not to be starting or stopping the central heating. The lights on the programmer work as normal,but when they go on or off, the central heating system does not respond. If I switch off the mains supply to the programmer (I think this is what the switch controls), then it turns off the system. I am having to use this switch to toggle the central heating system on and off manually.

I have a Glowworm fuelsaver MkII and Potterton EP2002 electronic programmer. I am guessing the problem lies in the programmer and will probably buy a new one, but any advice gratefully accepted.

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Turn off power supply & remove programmer from its backplate.

Turn power back on . Does this stop the boiler & pump firing ?

If pump & boiler stops then it is a faulty programmer (look for signs of corroded internal battery)

If ch continues to run then it could be a faulty microswitch in motorized valve or perhaps you may have a frost thermostat fitted somewhere which when 5 degrees or below brings on heating.

Turn off power supply before refitting programmer.
Thanks for this advice.

Have taken programmer off, as suggested, and turned power back on. System fired up for around 5 seconds, then turned off again. Left it turned off for a while, tried again, system did not fire. Inside of programmer looks fine, only a year or so old. Refitted programmer, put power on, and the system fired up again.

I'm a bit confused by that initial, 5 sec, response. Otherwise would assume it is the programmer. If you could clarify this for me I'd be grateful.


The 5 second fire up is a bit of a mystery
Have you got 2 or 3 port motorized valves fitted and if so what make
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I assume the motorised valves are the cuboid thingies sitting on pipes near the pump. Two are Appliance Components and one is Honeywell. A pipe goes in and a pipe goes out of each - is this two port? Our system was changed to a Megaflow a couple of years ago - not sure if this is relevant.


Sorry Nick but I cannot advise any further
You have 3 x 2 port motorized valves, 1 for ch, 1 for hw & 1 is a safety high limit valve for the megaflo.
I stop in my tracks as soon as anyone mentions megaflo I would advise getting approved expert in unless anyone else as any ideas.
Just to update you all - having removed the programmer from its base plate and re-fitted it, the central heating now works perfectly.

I can only assume there was a problem with the connection(s) between the programmer and the pins on the base plate - removal and re-fitting seems to have solved it.

I hope this helps others.


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