Leaking boiler

[RJH]

My Ideal Logic combi boiler has/had a slow leak, starting a week ago. The central heating water pressure has remained constant, and the water's clear/odourless.

The water's piddled down past the overflow boiler outlet grommet at a few teaspoons a day.

I isolated the boiler and took the front cover and swing down facia panel off, and water seems to have sprayed the insides of the boiler. I can't see from where. Droplets about half way up the case, and a small amount ponded at the bottom. Mopped it all up with kitchen towel a few days ago, and since dry.

Two things have happened since the leak:

A couple of very heavy rain showers that (unusually) were driven into the wall where the flue is located. I can't see anything untoward around the flue, and I couldn't see how water would end up where it has from that location. But still.

I did a flush/reverse flush of the system. I just lashed up some hose to the system and flushed it through for 30 minutes or so, until it ran clear - not a power flush.

As I say, it's been dry since I mopped the insides, so maybe a one-off? But I don't see how the water got there in the first place.

[Chris Hogg]

<Snip>

Don't some leaks self-heal? In a previous property, I had a very slow leak in a feed pipe to a toilet cistern. It was in a difficult place to access, was very slow and only actually revealed itself as moisture around a compression joint. I know it was a leak rather than condensation, because of the iron stain that slowly built up. But eventually it stopped, and I assumed that the deposited crud had finally formed a seal.

[Steve Jones]

[John Rumm]

Many boilers run the case at negative pressure - i.e. The air inlet is not a direct connection from flue to fan.

The fan sucks air from inside the case, and that in turn pulls air from the outer part of the flue (usually via a duct with a filter). Hence if water were driven up the outer section of the flue, it would end up being discharged into the case, rather than being blown into the burner.

[stevejones47]

[Steve Walker]

I had a boiler that had staining inside the casing, but no visible leak. It turned out to be a crack in the cast-iron heat exchanger. It opened up when hot and closed when cold.

The manufacturer agreed to replace it, even though it was by then out of warranty, when I pointed out that it was most likely a manufacturing fault that was hidden until the casing was removed for servicing - two or three months outside the warranty period.

SteveW

[tabbypurr]

Leaks can self-seal, but it takes a lot of leaking to build up enough crud. And nothing will seal if there's thermal movement. You can add isinglass to CH systems to seal leaks, but modern boilers often say don't so it's last ditch territory, and on those keep the strength right down. For thermally moving cracks it can reduce leakage but not prevent it - that can be enough to keep an old clunker going for years more.

NT

[Ian Jackson]

For car radiator leaks, we used Radweld and Barrs Leaks. I think one of them included cork dust. 'Natural' fixes included adding an egg white, or mustard. I once tried the latter, and it didn't half stink (and I'm not sure it worked). Would any be suitable for CH systems?

[charles]

Screwfix sell a heating system leak sealer/