Combi Boiler banging when using hot water.

[maax555]

Hi all, just thought I would post my problem on here before calling out an engineer. Hopefully it's a problem I can fix to keep the price down as its not a good time of year to be paying for unnecessary work to be done.

Ok we have a Potterton Promax HE Plus combi boiler which has been installed for around 6 or so years. The problem is that when we run the hot water taps or shower we get a very loud banging from the boiler. It really does sound like someone rattling the pipes in the heater cupboard. The water then runs cold and hot. It simply fades temp to hot then back down to cold in a continuous cycle until turned off. We have had the same issue around a year ago but it simply went away. There is no banging at all if we just run the radiators.
There are no leaks that I can see and the noise sound like it's coming from inside the combustion unit but it's hard to tell. I am competent in most DIY and Electricals but I won't mess with Gas. So if the problem is related to the gas side of things then I will need to get a Gas Safe engineer out. It would however be helpful to have an idea of the possible faults.

Any help appreciated.

 

[bazdaman]

Blocked plate is my guess can you measure some temp? Does the temp on front of boiler shoot up very high very quick? Does the pressure gague bounce?

 

[maax555]

Hi, yes the pressure gauge bounces or flickers at around its normal 1.5 level. After the water is turned off the pressure shoots up to around 2.5 and looks like it's dropping very slowly. The washing machine was running at this point which I did not realise so this behaviour may differ slightly when washer is off. When I have read about blocked plates I assumed this was only on the radiator side of things as it is sludge blocking the plates from the radiator.? We have had various radiators moved in the past and dishwasher installed by a relative. I am pretty sure on these occasions he has ran the hot water system dry (only from a tap)
. also when the radiators were moved water drained from downstairs radiator, once the system has been re-pressurised by simply turning on water and bleeding should there have been a chemical cleaner added? I can upload a short video of the boiler showing the temp and pressure along with the banging if it would be of any help?

 

[JMGas]

If your boiler is working fine on CH, then yes you 95% have a blocked plate heat exchanger. You can sonic clean them or replace it. Also get a magna cleaner on the return to the boiler to stop/slow it happening again. But its not a diy job

 

[maax555]

If your boiler is working fine on CH, then yes you 95% have a blocked plate heat exchanger. You can sonic clean them or replace it. Also get a magna cleaner on the return to the boiler to stop/slow it happening again. But its not a diy job

Many thanks guys much appreciated. Any idea of an estimate for this. I am in Newcastle upon Tyne as I imagine rates will vary across the country?

 

[bazdaman]

TBH its not difficult to remove the plate and clean its only 2 screws, then put some chemicals in plate leave for a bit and swill it out, i always clean them and they come up a treat.
If you feel competant enough after reading the manual then give it a go it will cost you a tenner for chemicals plus any time you spend on it.

 

[bazdaman]

Just checked new plate £101 the seals should be ok, if not you need 4 at £5 each retail.

 

[maax555]

Just checked new plate £101 the seals should be ok, if not you need 4 at £5 each retail.

Thanks for that. To get to this part do I need to break any gas connections? If not I will have a go myself unless I get a load of posts advising against it.
Really appreciate the help and advice.

 

[bazdaman]

No you dont, look in the manual and follow instructions its just a case of draining heating side from boiler and hw side then 2 screws and voila!

 

[gazplumber]

But its not a diy job[/QUOTE]
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