Boiler keeps switching on and off

fjon · 10-05-2011 10:30PM #1

My boiler was working fine for the last few months, but recently it seems to switch itself on and off quite a lot. It will run for a few minutes, switch off for a few minutes etc.
This is with all the radiators off by the way.
Any ideas - airlock perhaps?

Avns1s · 10-05-2011 10:33PM

Sounds normal, i.e. switching on and off with the thermostat on the boiler itself.

Turn on some of the rads and see if it runs normally and then you'll know whether its running ok or not.

fjon · 10-05-2011 10:38PM

Oh - never thought it was the fact that I turned the rads off that could have been causing it. Will try it again with the rads all on and see.
Just out of interest - why would the thermostat tell it to turn off and on again?
Bit clueless about this - has this to do with the heating up of the water?

fjon · 10-05-2011 11:04PM

And with all radiators on it still switches off, but after a longer time - will last maybe 5 mins, and switch off for 5.
Would this be normal again? During the winter when I had it on, it would run constantly.

CarrickMcJoe · 10-05-2011 11:11PM

I had a simular problem after moving the booiler to a new boiler house.
Turned out it was not getting enough air so after drilling a few airholes in the door it worked perfectly.

heinbloed · 11-05-2011 10:24AM

@the OP:

A normal behaviour. In winter the produced thermal energy is lost faster compared to summer(delta TCelsius or Kelvin).

Reduce the flow temperature to save on fuel during summer time, use the timer for DHW, install weather compensation. Insulate all pipe work beyond min. standards. To name just a few meassures.

A ST installation incl. a modulating combi-boiler is propably the next stop. When renovating the heating system. But ask a heating engineer for a wholesome concept.

youtheman · 11-05-2011 10:37AM

When you say it switches on then off do you mean on then permanently off (i.e tripping) OR cycling on/off/on/off etc.

If it is tripping then you need to see if there is an error code on the boiler and then refer to the 'makers manual'.

If it is on/off/on/off etc. then you need to check the controls first. If the room temp is, say, 20 degrees and you set the thermostat at 21 degrees then it won't take long to get the extra 1 degrees heat into the room. The first thing I would do would be to wind the thermostat up to max (for a short while) to see if it keeps the boiler on for longer.

You also need to check the 'deadband' on the thermostat, this is the difference between the 'click' as you wind it up and the 'click' when you wind it down. The bigger the deadband the longer between on/off signal to the boiler.

fjon · 11-05-2011 05:03PM

youtheman wrote: »

When you say it switches on then off do you mean on then permanently off (i.e tripping) OR cycling on/off/on/off etc.

If it is tripping then you need to see if there is an error code on the boiler and then refer to the 'makers manual'.

If it is on/off/on/off etc. then you need to check the controls first. If the room temp is, say, 20 degrees and you set the thermostat at 21 degrees then it won't take long to get the extra 1 degrees heat into the room. The first thing I would do would be to wind the thermostat up to max (for a short while) to see if it keeps the boiler on for longer.

You also need to check the 'deadband' on the thermostat, this is the difference between the 'click' as you wind it up and the 'click' when you wind it down. The bigger the deadband the longer between on/off signal to the boiler.

Thanks for the info.
It's cycling on/off, not tripping.
Try as I might I can't seem to find a thermostat anywhere though. In my old house it was in the hall, but in this apartment I can only find the timer. I'm assuming the dial on the boiler in the pic is the thermostat?
I've turned it up full, but it's still switching on and off, albeit with longer intervals now.

yoshytoshy · 11-05-2011 09:10PM

With your radiators turned off ,your hot water is probably balanced and so there would be a very small circuit.
I'd be inclined to turn the boiler right down ,during the summer months.

Back boilers have a very strong output and would heat up very quickly when only heating water.

Edit: I do these type of calls a lot by the way ,people suddenly notice things that they hadn't before.

youtheman · 11-05-2011 09:15PM

Thats not the room thermostat, that's the over-run thermostat (which is really only intended to be a back-up to the room thermostat). But if you have no room stat then the over-run stat has to do the job.

Have you tried winding down the the stat (shown on your photo) to re-set the boiler ?.

fjon · 11-05-2011 09:37PM

Thanks for all the replies guys!
It seems that the general consensus is that the boiler is working as normal then?
This is my first year in this place, and I've never had a back boiler before (I didn't expect to see one in a 5 year old apartment tbh) - I just wanted to check everything was working as intended.
The only "problem" with it is the turning off and on - the rads are mostly hot as is the water. Seems like it's working as intended so I don't need to bring this up with the landlord anyway.

yoshytoshy · 11-05-2011 09:48PM

fjon wrote: »

Seems like it's working as intended so I don't need to bring this up with the landlord anyway.

Your well within your rights to get the boiler serviced ,I'd feel safer if it was serviced or had been serviced in the last few months.

fjon · 11-05-2011 10:05PM

Ok, but it's only been there since January so I don't think that would be needed yet?

yoshytoshy · 11-05-2011 10:24PM

If it's only new then you shouldn't have any trouble. With the back boilers ,most people keep the thermostat turned down low because they give out so much heat.

Boiler keeps switching on and off

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