Noise in radiators (closed system) when hot water run

[Chris.tarry85]

Worcester Bosch 37 combi boiler on a closed, two zone heating system which in itself works fine - all radiators hot, quiet etc.

However, whenever there is a hot tap or shower run there is a small "gurgle" from one radiator when the tap is turned on, and another much louder "gurgle" around a minute after it is turned off. This radiator is in a bedroom so this is less than ideal!

This only happens when only the zone that this radiator is on is calling for heat - no issues when both zones are running or the zone is off.

I think this must somehow link to the movement of the diverter valve and some kind of shock wave being introduced into the system, but am at a loss as to where to go from here.

Can anyone suggest anything else I can reasonably check before I call someone in?

Thanks in advance

 

[Aire]

Have you bled all the radiators? Sounds like air in your system to me.

 

[Chris.tarry85]

Yep, no air anywhere in that zone - could it be affected by the other zone?

 

[Aire]

When did the problem start? Have you had any work done on the system before the issue? The noise your heating initially is the flow of water through the radiators stopping and air settling, this is happening when the boiler diverts as you call for hot water. The louder gurgle you hear after the tap is turned off, is the flow of water through your radiators starting up and this disturbing the settled air, there will be a delay with your boiler diverting back to heating so that's why it's takes a minute or so after the tap is turned off. Systems are generally quiet in their operation unless air is present.

 

[Chris.tarry85]

It's been happening for a couple of years to be honest - and whilst we recently had the radiator in question replaced this hasn't affected the noise.

I think this radiator may well be the lowest point of the system if that might affect it somehow?

Could there be air trapped elsewhere? Any way to force it out?

 

[Aire]

Try bleeding the radiator into a bowl, bleed it for a good couple of mins and see if any air comes out. Just keep an eye on the pressure.

 

[Chris.tarry85]

Thanks, will try that tomorrow - presume when you say keep an eye you mean to top it back up if it drops below 1 bar cold pressure?

 

[Aire]

Thanks, will try that tomorrow - presume when you say keep an eye you mean to top it back up if it drops below 1 bar cold pressure?

Yes that's right

 

[Chris.tarry85]

I tried this over the weekend and it did as you suggest splutter a bit when venting so I took about 2l out from this one radiator and then topped back up.

However it hasn’t made any difference.

I also noticed that the flow and return pipes in the airing cupboard (boiler is in attic) are quite gurgly when the system first turns on - this is a two zone system and the noise is before the zone valves.

So I think there is definitely air in the system, but am struggling to work out how to get out - would running the boiler in air purge mode perhaps help.

 

[Aire]

If there isn't any air vents in the loft, there will be one in the boiler, you may find your auto air vent has failed or scaled up. Unfortunately you are not allowed to remove the boiler cover. I would call an engineer to come and vent the system via the boiler and check the auto air vent while he's at it.

 

[Chris.tarry85]

Ok, so you wouldn’t recommend putting it into air purge mode myself?

 

[Aire]

Ok, so you wouldn’t recommend putting it into air purge mode myself?

You can try air purge mode but if your air vent is faulty it won't be able to purge the air anywhere