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Boiler Behaviour - is this normal?

hyeung Member Posts: 1

Looking for some advice on our boiler system.
Our have a Potterton Promax SL boiler combined with an unvented santon premium plus hot water system. I have a dual zone system so separate thermostats for up and down stairs and a separate hot water controller/scheduler.

The system is working fine in terms of requests for CH and HW.
However I’ve recently noticed some strange behaviour in that our boiler (in garage) was firing constantly approx every 5mins or so; it ignites and pilot light comes on, pump comes on and a few seconds later the boiler goes off whilst the pump runs for a few minutes and then goes off. This repeats every approx 5mins for about 1.5hr roughly speak starting at midnight thru to 1:30am. Now during then the CH and HW are all off, so no heat on radiators and the 2 zones valves are confirmed to be off (no led lights on the zone actuators)

As the boiler is in the garage, there’s a frosts stat attached (it’s tamper free) and there’s a there some thermostat attached to pipe work above the boiler (Honeywell L641B1004 set to below min setting).

I think the temp in the garage was around 7C at the time....
But question is why is the boiler firing so frequently? Is this normal behaviour?
If it was triggered by the frost stat, surely it would stay on until it reached temp and then switch the boiler off and not fire the boiler for 1–10secs, turn off and repeat every approx 5mins for about 1.5hrs?
Is there something wrong here? Or just normal operation. Would appreciate if someone could advise and explain what’s going on? I’m by no means technical in this areas as you can gather?



    EBEBRATT-Ed Member Posts: 15,628
    No, it does not sound normal . It appears the boiler is short cycling. I would have it serviced
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    I'm not familiar with that boiler, sounds like you are outside North America. If do some research on the freeze protection of your particular boiler. Sounds to me that is what is going on. If look into some type of constant circulation, or better yet build a "boiler room" around the boiler and not have to worry about the threat of freezing.

    The aquastat you speak of, can you post pictures of the boiler and the piping. Get a good picture of the whole setup including the pipes around it. We may be able to further help then.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!