Combi boiler makes loud banging noises, no heating

[duckbill]

So to start with, I'm not a gas fitter, I know I can't fix anything myself, I just want to know whether I should be worried or whether I can just live with this a bit longer.

When my heating comes on in the mornings, the combi boiler makes loud banging noises for about 20 seconds then settles down. Gradually this got worse, and eventually it would make the banging noises but then the heating wouldn't come on.

I had the idea to bleed the radiators, and that fixed it for a bit, but then one day it wouldn't come on even after I bled them. I got desperate and tried draining about a pint of water out of the bleed valve to see if that would do anything. It did and the heating came on OK.

I've just been leaving it on overnight as it only ever does this when it's first switched on after being cold overnight. Last night I switched it off though, and this morning I had to drain more water out before it would work.

What could be causing this? Here's a video of the banging noises.

 

[Jajodu]

I can't see clearly from the video, what is the pressure gauge on the RHS reading? A picture would be good.

 

[Madrab]

It's called kettling. The water in the boiler is overheating and that then causes boiling and the banging.

It's a circulation issue, basically the water cant get out of the boiler fast enough and it overheats. There can be several reasons for that. Lazy/bad pump, blocked heat exchanger faulty diverter valve, restricted pipework etc. I suggest an engineer visit to properly diagnose which system element may be at fault.

 

[duckbill]

I can't see clearly from the video, what is the pressure gauge on the RHS reading? A picture would be good.

In the video (taken in December) it's hovering around 1, today it's nearly 2. Just took this picture.

 

[duckbill]

It's called kettling. The water in the boiler is overheating and that then causes boiling and the banging.

It's a circulation issue, basically the water cant get out of the boiler fast enough and it overheats. There can be several reasons for that. Lazy/bad pump, blocked heat exchanger faulty diverter valve, restricted pipework etc. I suggest an engineer visit to properly diagnose which system element may be at fault.

Thank you! That's so helpful to know the right word to use. I will get on to my landlord about it.

 

[Madrab]

Yup, if you are renting then it's the landlords boiler and it's his responsibility to sort or replace it.

 

[ianmcd]

And get it done sooner rather than later you are damaging the top end of the boiler