White Water

[Vince]

We've had a combi-boiler fitted, early this year, to drive the heating and hot water. It seems to be working fine at the moment. The thing is though that the hot water comes out white and it takes a few seconds in the sink before it clears.

I know it's only miniscule air bubbles in the water and that they're harmless in themselves. The question is, what is causing the bubbles to be present in the water and is it inticative of any possible problems in the system?

I've had a good check around over the last few weeks and can't find any sign of leakage.

Thinking about it (though it's probably unconnected) - the central heating does not have a header tank but is fed from the mains via a valve. I check the central heating pressure periodically and let more water in if the pressure drops. The thing is, the pressure does drop so I'm having to allow a bit more water in every month. Doesn't sound right to me but I still can't find any leaks anywhere.

Any advice on the significance (if any) of the white water or central heating pressure drop gratefully received.

Thanks, Vince.

[Andy Jeffries]

Just wanted to let you know that I'm having exactly the same two symptoms. Hadn't worried about it until now! :-)

Didn't know if you wanted to know that you weren't alone!

Cheers,

ANdy

[Velvet]

Make that three of us :-)

I don't worry about the white these days - it's a lot less noticeable now the boiler is working properly at last and I can get a high throughput instead of a pathetic dribble out of it. Lower flow rates with a high temp just starting to form seems to be the time that the white shows up. I've wondered if it is scale that forms inside from the last cycle being broken free in minute particles when the boiler heats for the current HW demand, but putting it into a glass the water soon becomes clear so I don't think it can be that.

Both combi's I've had have had slow leak symptoms, but I rent, so I'm not going to pull up all the floorboards to check the rad pipes. I just top it up every so often (the new boiler is a lot less prone to this) - and also, given the filling loop is permanently connected, I wonder if it is going back through there despite a check valve.

I don't worry about either - I don't drink the hot water, so that's not an issue, and the pressure drop in the heating circuit is so small as to be negligible. One thing to consider is if you run the heating very hot the pressure may build up and the boiler vent slightly on it's pressure relief valve, mine's custom settable by the boiler engineers - or maybe a slow leak through the valve. Looking at the vent pipe may indicate if this is the case.

Velvet

[chris French]

An alternative possibility (though less likely given a newish boiler)) is a small leak via the diaphragm in the pressure vessel.

I've seen something similar.

[Andrew Gabriel]

When I installed central heating, I installed full bore isolation valves on the various branches. Partly, this was so I could isolate parts of the system to easily rule it out of any such leak, but also it was because I installed it slowly over a few years and wanted to be able to use parts of the system when other parts were incomplete.

You should inform the agent or owner. They might decide to have it repaired rather than fixing dry rot in a few years time. When I rented many years ago, my contract said failure to report obvious faults like this left me liable for consequential damages.

[Velvet]

It's not leaking anywhere near enough, and I pointed it out to the engineer who sorted the boiler after it was incorrectly installed. Haven't had to top up since then, so am presuming he did something that stopped it. I've been here coming up to 11 years now - told the original landlord, he wasn't concerned, at that point was topping up the boiler maybe once every few months, it would stabilise at about 1.25 bar, but not sit at 1.5 for months on end (which is how the system was set when I moved in). New boiler runs closer to 1.75, drops only very very very slowly, requires much much less topping up, which would suggest the rad pipework is sound. Boiler bloke pressured the system higher than 2 initially to check for leaks, nothing obvious then either.

Velvet

[MarkM]

The white bubbles in combi hot water is exactly this - dissolved air being driven out. It's just because the water has been recently heated from cold water rich in dissolved gas (air? oxygen?) without any time sitting around in a tank for the bubbles to come to the surface. If you heat a kettle of water, you can see the disolved gas coming out of solution long before boiling point.

[Ed Sirett]

The tiny bubble are dissolved gas in the water coming out of solution. This _may_ mean that HW temperture is too hot

As for topping up see the FAQ.

[IMM]

You can see this with some taps, especially aerated taps.

[Vince]

Thanks for all your answers. I'm much reassured. I'll not worry about the white water any more but keep an eye on the CH pressure.

Vince.