combi boiler overflow pipe leaking

cwrtcoed

Hi, I currently have a Worcester high-low 400 gas combi boiler. Recently water has been dripping out of the copper pipe overflow outside my house. I have checked the water pressure gauge and its showing nearly 3.5 bar. The expansion tank did show signs of slight leakage and when I pressed the air valve it didn't expel anything so I guessed that it was knackered. I have replaced the expansion tank but the water pressure is still the same so water is still dripping out of the overflow because its bringing the pressure valve into play.
Just to let you know the fill loop valve is not leaking, and the system was drained before replacing the expansion tank, I've pushed the air valve in the pressure tank and its showing pressure in it.
I'm on a water meter so its costing me cash every second

Mister_G

The normal operating pressure for a combi boiler is 1 to 1.5 bar. Yours seems excessively high.

cwrtcoed

Yes I know that, just wanted to know what else could be the problem or is the new expansion tank faulty

Hasbeen

Perhaps the high pressure on your boiler is activating the pressure relief valve?

cwrtcoed

Yes it is, I want to find out what's causing it

tacpot12

I know you've said that the filling loop isn't leaking, but that is the most likely explanation - the water has to be coming from somewhere. The only other alternative is that you have a leak inside the heat exchanger that is allowing water from the domestic cold supply to pressurise the central heating circuit.

If there is a way to isolate the domestic cold supply from the boiler you can check whether the pressure builds up with this isolated. If it does, it's the filling loop valve, if it doesn't, it's a leak between the central heating and domestic hot water sides of the boiler.

Ectophile

One possibility is a failed expansion tank (which shows up when the boiler is hot - the pressure will drop again when the heating goes off).

Another is that there is water leaking in through the flexible filler hose. Check that the valves at each end are both fully off. If in doubt, you could even take the flexible hose off to check for a leak. You're supposed to remove the hose anyway when you're not using it - but nobody ever does.

cwrtcoed

Ok guys thanks for your advice, I'll check these out

cwrtcoed

The heat X change is only 2 years old so that should be fine, there's a new expansion tank on there I rained it all again yesterday and refilled it but it's still the same pressure going up bit stumped now

cwrtcoed

Just a quick update' the new expansion tank was faulty, that's been replaced. However the pressure is still gong up, the filling loop isolated hasn't made any difference.
If I turn off the cold feed, both central heating feeds and drain the system the gauge shows zero. Turn the heating feeds back on the gauge still shows zero, but when the cold feed is turned on the pressure goes up.
So there's uncontrolled water coming from somewhere, one suggestion was through the heat X change, only other place other than that would be the manifold, but I can't see it being that.
Any other suggestions ?

Jonesy123

Does the pressure go up when the heating or hot water isn't in?
It sounds to me like an undersized expansion vessel. That's one of the most common reasons a system pressure would rise that high, and domestic plumbers aren't usually that au fait with sizing them correctly