Posted this on another forum elsewhere but didn't get much feedback, so hoping might get some help here !

My elderly fathers bungalow had a convential heating system with a header tank until a few years ago when the header tank was replaced with a pressure container to fix recurring air problems with the system.

It's worked fine until last week when the system started making load banging noises, and on inspection the pressure tank showed low pressure and had to be topped up with water by turning on the isolating valve to it until the pressure was restored.

But this has had to be done almost every hour to keep the pressure up.

Even when the heating system is switched off overnight, the following morning the pressure has dropped again and the tank needs refilling.

The really puzzling thing is that there is absolutely no sign of water loss anywhere, via overflows, damp ceilings, under floorboards or anywhere else. Where is it all going !

The system is covered by a British Gas maintenance contract and the plumber and his foreman have visited a couple of times and seem to have little clue what to do, but are returning Monday to check out whether the heating coil in the hot water cylinder is leaking through into the cylinder contents. Not sure this will be the problem though as I say the problem still occurs overnight when everything is off and therefore presumably the valve that switches on the hot water circuit will closed ?

Not sure how problems with the pressure container/valve itself would lead to water loss from the system and why it can't be traced anywhere, which I guess is what has made them suspect the cylinder, but any other thoughts or advice gratefully received !

Could it be that the pressure relief valve is faulty and leaking air which causes the pressure to drop, and then the water topping it up is restoring pressure temporarily until more air escapes ? Any way to test this or perhaps I'm going in the wrong direction ?

Thks  ???

How would I go about testing it Greg ?

Should I get air instead of water or the other way around ?

Cheers

The bubble will have a bicycle type valve on top - undo the cap - with a screwdriver or such like - give the valve a quick press down to see if you get air or water - if you get water it means the membrane inside has a hole / split which would mean it cant expand and the pressure relief valve will operate.

Another possibility is that you could have a small leak on a radiator valve gland which when the system is hot will not be noticeable but overnight when the system is cold is enough to lose its pressure.

If the cylinder coil has gone - chances are that you will notice it by the colour of your hot water. ie brown / dirty.

When you have to top up, does it need much water to re pressure?