Loud banging noise when CH/HW fires up

Joined
10 Jan 2008
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Location
Buckinghamshire
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United Kingdom
Hi everyone,

I wonder if you could help me. I recently moved into a property and up to the last couple of weeks everything has worked fine, however recently I get a loud banging noise that sounds like pipes "twanging" loudly when the CH comes on. I've got a list of info related to it for you:

(1) The Boiler is a Celsia (not sure of the model) but I don't know it's age
(2) The system uses two tanks that are situated in the loft - one very large and one small (we have a standard sized 3 bed semi) and a tank in our bedroom
(3) The CH and hot water do work fine and heat up quickly
(4) On speaking to a friend he suggested turning the setting on the pump down to see if it solved it. This worked, as it was on it's highest setting (3). It's a grundig pump. However, when I turned the pump down to setting 2 last night I noticed that the boiler cycles constantly instead of coming on for a while, then turning off when the desired temperature has been reached, and then coming on again a while later when the thermostat tells it the temp is low. Essentially, the bolier fires up, works for about a minute then goes off. One minute later it comes on again. Each time it does this the pipes under the floorboards upstairs make a ticking noise (I assume expansion).
(6) This morning I turned the pump back to setting 3 and the system seemed to work as normal again (apart from the loud bang at the start)

Regarding the bang noise:

(1) I think it may be when the hot water comes on rather than the CH - although I'm not certain. I have the HW and CH set to come on twice a day and did try turning off the HW one day and didn't get the banging, however I failed to mention before that this banging doesn't always happen - it's random in it's occurence.

(2) Another important point is that this banging can occur from a cold start too. That is, it often occurs at 6am when the HW and CH come on (sometimes waking my wife and I up)

(3) I recently had to clean the filter on my shower and on doing so a lot of reddish sludge had built up and turned the flow into a trickle. The shower worked fine when we moved in last October and this blockage must have happened a couple of weeks back.

(4) A plumber had to drain the CH and refill it recently too as I managed to bang a nail into a pipe whilst decorating (yes yes - i'm an idiot). He did put inhibitor in the system though and fully vented the radiators.

As said before, the HW and CH do work fine however I'm worried about the loud bang that occurs randomly a few seconds before the boiler fires up (at any point in the evening or morning - including a cold start)

Can anyone help? - do I have air in the system? - pump problem?

Thanks everyone in advance.
 
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Did it bang before the plumber drained the system ? From what you describe it sounds like air in the system. Check that it is fully bled, especially the bleed pipe by (normally just above) the pump.
 

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