worcester 24cdi banging/straining

[greenockboy]

Hi,


Just looking for some opinions on this. As it will be handled by gassafe engineer one way or the other!


To cut long story short(ish) but keeping detail:




We have a Worcester 24cdi combi boiler, CH system is plumbed in as open vented with a F&E tank in loft. And boiler supports 8 radiators. Basically when hot water been running for a while (running bath) and it gets switched off the boiler starts banging and clunking loudly for say 10-15 seconds, in the upper part of boiler. It doesn't do this though if we run the hot water and central heating at same time, only when its just hot water as described. Also we can sometimes hear what sounds like a fan/pump struggling also when hot water is running.


** we had some work done on radiator valves in April and system was drained downed then (not powerflush) - desludger added, allowed to run, drained down, refilled with inhibitor added


British Gas have been out twice on homecare call out:
First Engineer: You need a new boiler and a powerflush - £700 please for powerflush would you like me to send someone to quote for new boiler !
Second Engineer: You dont need a new boiler but need a powerflush - £700 please


Got a second opinion from a local gassafe engineer and I also emailed Worcester:
Independent Gassafe guy: He spoke to worcester, they agreed with what he thought - will be pump or pump over-run. Change / check these before thinking about power flushing
Worcester reply back to me: As only happens on hot water suggests system is ok, unlikely to be solved by powerflush.




Any thoughts anyone? Are BG basically on the rip off asking for power flush. We have them coming back out again for 3rd time. And will be advising them what the independent engineer and Worcester said.

cheers !

 

[Masood]

Agree that if the problem only happens on HW circuit, sludge is not the most likely cause. Although I am a little suspicious of the pump overrun diagnosis, as the banging doesn't occur when the CH is running. When the problem occurs do you see system pressure rising and/or water coming out of the PRV? Wondering if your expansion vessel has depressurised. When the CH is running, pressure will be absorbed by the F&E tank, but when only HW runs, the F&E doesn't form part of the primary circuit, so cannot absorb pressure rise.

Just a thought...

 

[greenockboy]

Agree that if the problem only happens on HW circuit, sludge is not the most likely cause. Although I am a little suspicious of the pump overrun diagnosis, as the banging doesn't occur when the CH is running. When the problem occurs do you see system pressure rising and/or water coming out of the PRV? Wondering if your expansion vessel has depressurised. When the CH is running, pressure will be absorbed by the F&E tank, but when only HW runs, the F&E doesn't form part of the primary circuit, so cannot absorb pressure rise.

Just a thought...

Hi there. Thanks for replying.. CH system isnt pressurised, CH feed is fully from F&E tank in loft and not through mains. So no pressure in system. Not sure why its plumbed in like this, was already there when we moved in few years ago !

 

[SafeGasInstall]

problem you have i think is having a open vent system on ch , must be pressurised !!! get local engineer to seal system or post your location and trusted plumber from here and provide you with a quote

 

[Masood]

Hi there. Thanks for replying.. CH system isnt pressurised, CH feed is fully from F&E tank in loft and not through mains. So no pressure in system. Not sure why its plumbed in like this, was already there when we moved in few years ago !

Yes, I understood that! There will be a rise in pressure when the system heats up. An open-vented system will allow expansion through the open vent pipe, into the F&E (feed & EXPANSION) tank. There is still an expansion vessel inside your boiler. When you use the HW on its own, the diverter valve limits flow to just that circuit, so your F&E tank can't absorb/take up the expansion, only the inbuilt vessel can. If this has depressurised, it could cause banging and rattling noises. It's worth a check.

 

[greenockboy]

problem you have i think is having a open vent system on ch , must be pressurised !!! get local engineer to seal system or post your location and trusted plumber from here and provide you with a quote

actually one of them (BG eng) mentioned / recommended to get it sealed ...
bit worried leaks will start to appear at joints if we do that as system has never been under pressure .. we did used to have the old style dual-entry valves on radiators also, got all of them upgraded to single entry TRVs not so long ago though..

 

[SafeGasInstall]

Must seal system but use NOT BG !!!
Will cost you a lot less with a local heating engineer !

Where about are you ?

 

[greenockboy]

Hi again, west coast Scotland - quite a bit away from yourself 🙂 ... will see what this BG guy says tomorrow, but if its same old "powerflush" story we'll deffo be getting a local engineer to deal with it

 

[SafeGasInstall]

forget about BG , they all same old power flush every where ! ask friends or family members to recommend a heating engineer to do the job .
you can post your location here some one might be not that far from you



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