Keep loosing pressure on gas boiler

Question

I keep losing pressure in gas boiler, after I top it up within an hour the boiler is empty of water, also when I turn boiler of after about 30 mins I get very loud banging noise from loft area as if someone was harmering the pipes and this would last for hours.
Not sure if I have a leak but can not see any signs on ceilings with damp patches.

Billy · Accepted Answer

Unless you can see any visible leaks Sounds like your pressure vessel and prv need replacing, let us know if you want doing and we can do for uk

Kind regards 
Bill

Kevin · Answer

Hi There,
There is either a leak in your system or possible pressure relief valve faulty.
Regards,
kevin

Geoff · Answer

After you top up the pressure and turn the heating on check to see if the boiler pressure rises above 3bar. If it does the noise is the pressure relief valve discharging and the pressure vessel inside the boiler is faulty

Robert · Answer

Expansion tank probably has damaged diaphragm causing over pressure and airlock

Geoffrey · Answer

Don't attempt a repair yourself. You need a engineer to sort it for you. There are safety implications involve so stop using the boiler as it sounds like it going from a minor proble to a more costly one.

Rochshane · Answer

Expansion vessel either needs to be recharged or replaced if diaphragm inside is split & with the hammering noise could be an air lock

Peter · Answer

Pressure vessel gone by sounds of it . Is the pressure rising rapidly once heating on? Banging possibly pressure relief opening/closing rapidly to release pressure , could also be overheating due to blockage or pump knackered

Hamel · Answer

You most likely have either a torn expansion vessel, or faulty pressure relief valve.

Can you see any water puddling anywhere

Liam · Answer

Hello

The loss of pressure can come down to a number of things. The main thing people think of is a leak. if there is no damp of visible signs of water anywhere then a simple test at your boiler can tell if its a leak from within the boiler itself or the pipework within the property. Yearly boiler service should always bring up any issues within a boiler.

As for the noise, this sounds like what is called water hammer where pipework has not been clipped or fitted properly so when appliances are used for example the toilet it can create a hammering noise throughout the house when filling up again after being flushed. this happens a lot in homes with gas combi boilers where all the supplies and pipework are under mains pressure. And is more common in homes that have been converted from oil to gas where the pipework and appliances were once only ever gravity feed and not under mains pressure.

Keep loosing pressure on gas boiler

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