Boiler loosing pressure tried it all

Firefrog11

Hi I have a 7 year old boiler that has been regularly serviced, last winter it started loosing pressure and needed topping up ever 3 weeks, I had the expansion vessel changed and have checked the pro valve, but still it lost pressure. Then when the weather started to get warm and the central heating stopped being used the pressure problem went away, boiler still being used for hot water. Then this winter when the central heating came back on the pressure loss returned again.
So it seems that the pressure loss is a result of the heating system being used, I can’t see any leaks anywhere no water stains in floors of ceilings, no dripping pro and a new expansion vessel.
I dont understand why when the pressure drops I loose both heating and hot water, but the pressure only drops when the heating is on.
I would really appreciate any advice.
Kind regards

tony541

Hi, Just had a similiar problem at my house, re charged the expansion pressure tank and no drips anywhere. In the end the BG engineer put a sealant in the radiator system and that has solved the problem and that was 2 weeks ago.
Good luck.Tony

boliston

using only hot water will only increase the system pressure by about 0.5 bar but heating the radiators will cause a much bigger increase and if the expansion vessel is not correctly working water will be ejected via the pressure relief valve so once the system cools down there could be zero pressure which would stop both heat and hot water. If you can see the pressure climb over 3 bar when you first turn on the heating then that would indicate an expansion vessel fault - a temporary solution would be to turn down the bolier temperature dial, but that will mean radiators are only warm rather than hot (should not have any effect on hot water temperature)

lewishardwick

Take off the front panel of the boiler and look for leaks there.

If the rads aren't leaking, if the prv isn't leaking, the expansion vessel has been replaced, then there's a hidden leak somewhere.

Could be the heat exchanger that's faulty...

Alex1983

Where does your downstairs pipework go, does it go in to concrete floors or suspended floors or is it surface mounted? What model boiler do you have? How many radiators do you have on your system?

You need to work out if it’s the boiler leaking internally and the water disappearing through the condense pipework or if it’s from the heating system.

You can prove it 1 of 2 ways, you could shut the boiler flow and returns off with the system repressurised and leave it off for a few days, if it continues to leak the problem is the boiler if no leaks you can open the valves back open and if you loss pressure straight away you’ve proved the problem is on the heating system somewhere.

The other option is to tape a sandwich bag to the PRV and another 1 other the condense pipe and leave the boiler off for a while and see if you have any water in either.

Firefrog11

Hi everyone thanks for your replies. I think the next thing I need to do is turn off the flow and return to the rads and see if I have a leak in the boiler which I suspect is the issue. I live on the top top floors of the building and the person below doesn’t have any damp patches on their ceiling. I’ve already checked the PRV and no leaks. However I do sometimes get a spike in pressure when the heating comes on but not always do it could be that which would explain why I only need to top up every couple of weeks.

What is the reason for a spike in pressure?
I wonder if it happens only when the hot water is running when the heating comes on.
I will have to check.

Expansion vessel is new and has been pressurised, boiler is a Valliant. Not sure what model as I’m away on holiday at the mo.

I have 6 rads over 2 hoist and timber floors.

I’m not keen to add a leak sealer to the system as I’ve heard bad things about it and would rather fix the problem properly but may have to resort to it. Any ideas on that would also be very welcome.
Thanks again everyone.

Alex1983

If your top floor flat with no water coming though the ceilings below and your expansion vessel has been recharged then I would expect it to be the heat exchanger that has failed.

The heat exchanger will be very expensive so I would definitely isolate the boiler and prove the boiler is at fault first.

Firefrog11

Hi Ok I'm back home now so i will start to do some more investigating, ill isolate the boiler first and see if the problem is there.
Thanks everyone for their advice, much appreciated!