Why is my combi boiler losing pressure?

[MagicWorkout]

Its been doing it for a while, I need to "top it up" every couple of months, but since the heating's on it's every few days.

I had it serviced in August and the plumber said the boiler itself is in good order, nothing there to explain it, there must be a leal somewhere else. He had no interest at all in helping me find the leak but said the radiators are the most likely place.

I've checked around all the radiators and can find no leak.

What do I do next?

We had a very small leak in one of our radiators which cause the pressure in our combi boiler to drop. It was very small leak so took some time to find.
Can you put a piece of paper towel below the radiator valves and see it gets wet.

I'll have another look but I really did check carefully

Any pipes sunk in concrete floors? We had this in a previous house and tried everything to either fix at the boiler or find a leak. Eventually we isolated the rad to the kitchen which was piped under the floor. Sorted it straight away. It meant no heating to the kitchen for a while but could be sorted by rerouting the pipe work above the floor.

Have you tried a fernox type leak sealer? Not ideal but if it works....

We've had this. It went on for a few years partly due to covid as I knew how to top up the boiler so it wasn't classed as an emergency. Eventually it was every day that I needed to top it up.

It's eventually been fixed after several call outs. It was a valve/s inside the boiler that needed replacing.

Good luck op

I agree with @Nospringchickendipper,

I have the same problem , one of my rad's has a very slow leak , it took me ages to find it I put a strip if kitchen roll around each in /outlet and the valves .

I found the leak but I haven't actually got round to doing anything abou the leak yet tho

We had this, it was a leak from the back of the boiler.

We had the same problem. Turned out it was some kind of inflated bladder thing inside the boiler which had been taking in water when it wasn’t supposed to, displacing the water that was supposed to be there and causing a drop in pressure. Something to do with the steam venting outside getting back in? Sorry, I’m a bit sketchy on the details. It needed to be removed and replace, and actually the problem had caused a lot of corrosion inside too, so other parts had to be replaced at the same time. Took AGES for the plumber to figure it out but he was the person that installed it and it was still under warranty so he persevered. Would have been an expensive job if it hadn’t been covered.

If the boiler has been checked out, then it's likely a tiny leak somewhere - and that might be under the floor.

A fix might be leak sealer - it's a bit of a gamble, but often works and might be worth a go first. I'd recommend www.toolstation.com/fernox-f4-central-heating-leak-sealer/p83815

Watch some videos on how to use it - if that doesn't fix it, it's a bit of a painful process with a plumber disconnecting different bits of the system and leaving them pressurised to see what area has the leak. Long and difficult :-/

Good luck!

Agree with the leak sealer suggestion, especially if it's a large system and you've checked what you can easily.
It sorted ours.

If you haven't done it already vent all the radiators, it probably won't make any difference...unless you find one that is full of air.