IDEAL ICOS HE 15 - Mind of its own

21 Apr 2020
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United Kingdom
Hi there.
We have an Ideal ICOS HE15 centtral heating boiler. Until now it has been working fine and was only serviced in January.

Last two days it has developed a "mind of its own" where outside of the programmed times, the boiler starts up, cuts in for a few seconds and then shuts down, going into standby mode again. The "c" shows in the display, suggesting it is on, whereas normally it would show a "0" when it is not in the program cycle. I can hear it cavitating inside, as none of the zone valves for the heating or water are opening and the pump is not running.

Any thoughts would be appreciated before I call in the service engineer - if I can get one at this challenging period.

I have done the usual "reset" and full power off, with no success, and there are no fault codes showing.

Thanks in advance.
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sounds like a sticking end switch on one of your zone valves rather than a boiler fault, but you do have a really poor boiler and the PCBs on them is total crap

Surprised at the comment about the boiler quality - not challenging it - as my niece's husband works for a building firm and both he and the engineer who serviced it two months ago said it was a good boiler.
I just have one question about your comment on the zone valve. If the issue is happening outside of the scheduled program times, how does a sticking micro switch on a zone valve cause the boiler to fire up, as there should be no power there, or signal to boiler?
I was going to suggest the microswitch until I noticed you said the pump is not running, I would hazard a guess that the pcb has gone faulty and to answer your question about the valve there is a permanent live in the valve that causes the boiler to fire regardless of room stat or programmer settings if the switch gets stuck.
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These are the zone valves I have. Drayton for HW and the other for CH. The CH actuator was changed a couple of months ago. The pump was new 3 months ago.


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I can hear it cavitating inside, as none of the zone valves for the heating or water are opening and the pump is not running.
do you mean kettling ? if it is cavitating then the pump IS running and it is probably a stuck end switch as already said

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