Heating system losing pressure

[Octoberfishing]

We recently had our boiler serviced, and the engineer mentioned the boiler pressure was low, and reminded us about how to top it up, which we did.

A day later, the pressure had dropped down almost to zero again. I topped it up again.

24 hours later, it's dropped right down again.

There are no obvious signs of a leak / radiators are getting warm and we haven't recently bled any radiators. Very occasionally (as in once a month) the boiler will make a dreadful banging sound, turn itself off and on again, then all is well!

Does anyone have any suggestions (I remember @pigletjohn was an expert)? We have British Gas cover, but there's a £60 excess fee, and I'm loath to call them out if they just say "oh yes, your pressure's low, I've topped it up for you".

The boiler is an Ideal, 7 years old.

Mine drops pressure every now and then usually when it’s been a particularly cold spell. It’s been serviced recently with no issues. Radiators don’t need bleeding and they are evenly warming as they should and it’s not making any strange noises and no leaks anywhere. I just repressurize it as I’ve been shown and it sorts itself out.
I’m would get some advice though if it’s making a funny noise or happening a lot

What kind of service did you have? A safety check or a full strip down and clean?

When I had that kind of drop in pressure in a short period of time it was a leak - a flooring fitter had hit a pipe installing flooring over the summer and it had slowly dripped into the ceiling below for three months before it was noticed. I would advise getting it looked into to be honest.

The only times I've ever had rapid pressure drops was when there was a leak somewhere in the system.

If it's that big a pressure drop and that soon after the service I'd request they come and look again with no callout charge.

I watch leak detector uk on TikTok. Whenever he is called out for boiler losing pressure it is always a leak somewhere. Amazing how he finds them, even when other engineers have failed.

This sounds like my kind of YouTube rabbit hole!

It was a boiler check and service - but not a full strip down.

My Boiler pressure used to drop, my OH topped up the pressure roughly weekly, not obvious signs anywhere of a leak. I have a downstairs bathroom, that needed replacing anyway. The bathroom fitter/builder said while he was redoing the bathroom he may as well take the opportunity to lay and reroute completely new pipework. The leak was a pipe under the floor tiles as the concrete was wet.

Boiler pressure solved.

I had a similar problem but it was the ….. can’t remember the technical term…. Expander or inflator or something?? In the boiler, part of the valve system I think. It needed replacing. Sorry, that’s not hugely helpful but thought you might like to know it’s not always a leak!

Expansion vessel? I had to have one replaced in my old house.

We had a similar problem last month and it was the expansion vessel.

When we had similar problems it was the expansion vessel. Iirc, the first time the engineer was able to re-pressurise the system, but when it went again it had to be replaced.

Yes, I would too.

We've had it recently- it was a slight leak from a radiator in one of the rooms.

Another person here with expansion vessel
Issue being the problem. It was an old boiler and kept going for another year or so.

Expansion vessel or leak- dug up my floors twice thanks to leaks in concrete.

When I had this problem it was because a valve in the expansion vessel was broken. It wasn't cheap to fix, but once done it did solve the problem. Is your overflow dripping?

My 5 year old Ideal Boiler did exactly the same thing 18 months ago, following a service.

Ideal Boilers are insured for 10 years providing you have followed the Annual Service protocol.

I called Ideal, they came out, replaced the internal Pressure Vessel and an Air Valve. It has worked fine ever since

We had pressure loss in a house that had not any tradesmen in bashing floors or walls and we checked for weeping around every radiator.

Ours was a cracked heat exchanger in the condensing boiler, it was hidden from us as the water drained out of the condensing drain! Apprently this can be a feature of Ideal boilers of a certain age and was only a 45 minute fix to strip replace and reassemble by a plumber organised by Ideal via their help line.

I am not recommending that you do this, however to find it I turned the boiler off when cold, got the system up to pressure and placed a small clear plastic bag under the condense drain pipe which I held in place with an elastic band. Waited 24hrs, the pressure on the gauge had fallen and the bag partly filled with water, this was a clear indicator of a leak within the heat exchanger. I then reconnected the condense drain and called Ideal.
If there had not been water in the bag I would have moved onto suspecting the expansion tank.

After you've topped it up, does the pressure rise a lot when it gets hot? And then fall a lot when it goes cold?

Random very simple fault on mine took a lot of investigating to figure it out (expensive) so check this…
do you have an digital pressure reading window or is it the little manual circle with an indicator?
if you have the digital window - check the manual circle cos maybe the digital window is losing its connection and a simple little piece or wire (or similar) just needs replaced.
This had gradually gotten worse and worse for years for us…right pain i am so happy I don’t need to worry about boiler losing pressure!

Run the heating and after 45 minutes have a look at the outside wall that the boiler is fitted on. Check water isn’t leaking from the little copper pipe sticking out the wall

We had this due to a leak under the floor, I agree topping up the boiler is something needed, occasionally, but if you are needed to do it often, there’s a problem somewhere.

Oh I'm not sure. I will check and report back!