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Central Heating

The glow worm he combi keeps on losing pressure!

i am being told it will takes hours to fix it? what is wrong and how much the real cost might be?

6 Answers from MyBuilder Heating Engineers

Best Answer

Everyone is correct here. The bottom line is water is escaping from the sealed system. the question is where from. It will either be on the pipework or because the expansion vessel has failed. This would normally become apparent because the pressure guage would rise from 1 to 3 bar in literally ten mins when you turn the heating on. followed by either quite a horrendous noise from the boiler as the pressure relief valve dumps the excess pressure. putting a paper cup over the end will let you know that water is being discharged but that could be just because the presure relief valve is letting by. If you are only having to top up once or twice week it is a minor leak and yes any leak sealer added to the system should cure it. That would cost around £40-£50 supplied and fitted
If you are topping up everytime you put the heating on it will probably be the pressure relief valve and that is a timely job as in most cases the boiler has to come off the wall. An external add on expansion vessel would be cheaper, but not so aesthetically pleasing. Good luck, hope this helps.


Answered 17th Mar 2011

As mentioned earlier it could be your expansion vessel (the red vessel inside the boiler)thats lost pressure or the membrane inside has failed, press in valve on the vessel and if water comes out its had its day. Also, trust Plumbers the majority are good lads trying to make a living!
ps Im a joiner and not a plumber, would be good if a plumber would confirm the above is correct.


Answered 27th Feb 2011

Normally a pressure drop on the combi boiler is either a weaping valve on the boiler itself, but more likely a leak within the flow and return system to your radiators. It does not take much to drop the pressure on a combi. Check all radiator valves and bleed nipples, make sure everything is dry. You dont say whether your piping is in copper or plastic, but it could be that every joint would need to be checked to find the leak. Normally you will see a leak if its from the upstairs piping (damp patch on ceiling) so you can then concentrate on the groundfloor. Good luck, the price will depend on the time to trace to fault and the materials to effect the repair.


Answered 27th Feb 2011

sounds like a leak on your system OR check the pipe outside as the blow off could be leaking via this pipe.


Answered 27th Feb 2011

hi , it depends on what is causing the pressure loss , if it is down to a small weap on a fitting then it could take hours to find it but it would be easier to put a bottle of fernox leak sealer in the system. it could also be down to the pressure vessel in the boiler needs changing but this would take hours to carry out.


Answered 27th Feb 2011

Mr Chippy is right if the expansion vessel has gone the boiler would be blowing water outside when running, the best way to check is to put a paper cup on the copper pipe that runs outside, if water is present in the cup when the system is running. Then looks like a new expansion vessel. Disscuss the possibilty of fitting an external vessel as this is much cheaper


Answered 28th Feb 2011

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