Central heating pipes 'banging/knocking'

[callum84]

Hi,

I am looking for some guidance regarding a problem that has developed with my central heating system.

A couple of days ago, the pipework started banging/knocking when the heating was going on and when it is cooling down, this banging can vary from a large thud to a series of regular bangs, the later usually when cooling down which then becomes less and less frequent until it stops - this has just started to happen, we have had the property for 3 weeks and was working with no banging etc until around 3 days ago.

Its an alpha combi boiler with radiators/heated towel radiators the radiators have thermostatic control valves (apart from one which doesnt)

I was wondering if anyone had a view/suggestion on what this could be before I have to call out a plumber/CH engineer.

I have looked online at things like, boiler pressure, pipes not properly clipped, air trap?!? All very confusing to me to be honest.

The boiler was installed in Jan 2011, and has a 5 year guarantee, I am unsure if new pipework would have been installed at the same point.

The crawl space sub floor is only approx 500mm so I am hoping it can be rectified without having to lift carpets etc, especially as some floors are tiled.

Regards,

Callum

[GrahamM]

I assume you have checked system pressure and have bled all radiators.

Open up all thermostatic radiator valves (TRV's) fully and try that.

[callum84]

Thanks GrahamM.

I am going home tonight to bleed the radiators, the banging seems to be situated at the opposite end of my property to where the boiler is, I think I will bleed those radiators first??

If a TRV in say a bedroom is set less than the bedroom next to it, can that cause issues??

[callum84]

Just bled radiators, only water came out no air, boiler pressure sitting at 0.75 bar?? Slightly below what it should be I think? Anyone have any suggestions?

[P J F PLUMBING]

Call your gsr engineer he will sort it for you

[callum84]

Is the low pressure contributing to the noise in your opinion?

I apologise if this is a basic question, but should rads heat from top to bottom or bottom to top?

The rad in the room I think most of the noise is in heated from the top an generally worked down the rad to the bottom? Is this normal?

[glenno1]

Bottom to top(heat rises)

[GQuigley67]

is it top entry TRVs ?

[GrahamM]

Top system pressure upto 1-1.5 bar, open up all TRV's fully & run system to temperature.
Did you try this?

[jase158]

possible solutions

1. radiator valves are not shutting properly and causing banging, try taking head off and making sure valve is loose
2. Pipes need clipping down, try to find exactly where noise is coming from and check under floor for loose pipes
3. noise reducer can help get rid of noises, this can be added to system via tank in loft or radiator
4. Powerflush, system might be dirt ridden and banging

Finnaly try to think of anything that you have done in last few days, turning heating on? turned radiator valve off? pressed any buttons

[callum84]

No it is TRVs at the bottom of the radiator.

Havnt tried to change the pressure, really wouldn't know where to start I am afraid. I hav bitten the bullet and arranged a service for Friday (boiler was installed jan 2011 and has not been service yet.

Nothing different last few days jase158, tried system again tonight, but set boiler to a lower temperature, the noises didn't seem to be as bad although were still apparent?

[GQuigley67]

you need to let engineer know of this problem as it wont be picked up on a service

[phpaul]

Is the low pressure contributing to the noise in your opinion?

I apologise if this is a basic question, but should rads heat from top to bottom or bottom to top?

The rad in the room I think most of the noise is in heated from the top an generally worked down the rad to the bottom? Is this normal?

no its not the flow direction to the trv sounds wrong ask ur gsr guy to check it out . get the pros in its not worth ****ing about with .

[callum84]

I will highlight the noise issue etc yes, i explained it on the phone to another guy when booked service(not sure if was qualified) they said it could be 'normal' expansion/contraction with the pipe work, it just sounds to 'rough' to be normal in my humble opinion, but we will see.

I just hope that it doesn't mean lifting all the floor finishes to get a look at the pipe work, would be a hell of an amount I work to be honest ie lifting plywood/hard wood flooring (kitchen) laminate (hall) and carpets (bedrooms) but I suppose if needs must, or maybe the plumber will have some tricks of the trade to dingoes any issue.

Thanks for the info guys, much appreciated, great forum!!

[GQuigley67]

does it happen when you open the hot tap ?