CH "bubbles"

[Fred]

Hello,

The last couple of says I have heard "bubbles" in the central heating. Not constantly but once or twice a day I have heard what sounds like bubbles running through the pipes. The bubbling lasts a few seconds then stops.What does this mean? Surely if there was a leak, I'd have bubbles constantly? I have not added fresh water so there should not be any air in the system, unless it is filling from the header tank without my knowing.

Thanks,

[Lobster]

You can still get gas in there without a leak especially due to corrosion if you haven't got any inhibitor in there (have you?). The bubbles are probably reaching a high point in the system when you switch on, and then stay put.

Try bleeding the radiators now; then you need to solve the bubble-formation problem...

David

[Roger Mills]

It sounds as if some air is getting in - unless it's hydrogen caused by corrosion due to a lack of corrosion inhibitor in the system.

Is it an open vented (i.e. not pressurised) system? Is there at least *some* water in the fill and expansion tank (the small tank in the attic, not the large cold header tank for the HW system)? Does the system pump over? [i.e. does water constantly flow out of the vent pipe back into the F&E tank when the system is running?]

[Fred]

Hello,

There is Fernox inhibitor in there, I filled it myself after fitting a new radiator a year or so ago.

It is an open vented system so I shall look in the loft to see whether there is "pump over". What would cause that?

Thanks.

[Roger Mills]

The first thing to check is that there is some water in the F&E tank. It's quite common for the ball-valve to stick shut since it is used so infrequently. If the tank runs dry due to evaporation and/or slight leaks in the pipework, air is very likely to get drawn in.

Pumping over is usually caused by faulty system design - with the pump in the wrong place, or the fill and vent pipe connections into the flow pipe being too far apart. If the system has worked happily for years without pump-over, it's unlikely to start suddenly unless something changes - such as fitting TRVs to the radiators, or increasing the pump speed.

[Fred]

I haven't got the ladder out to look yet but I'm pretty confident there will be water there. Last time I looked I remember the water was quite murky. I added the fenox first so I think that got flushed into the pipes, leaving none left in the tank. I've been meaning to drain the tank, clean the "stuff" out and add some more fernox to stop it coming back.

I did add trvs the other year. Are you suggesting that when all the trvs close, the water is pumped through the vent into the tank? I'm sure it isn't because I left a couple of radiators (bathroom and hall) without trvs. Could it be that that was not sufficient?

If this did happen, how does it explain the bubbles? Is it that when the trvs open again, the water is drained back from the tank and that it gets aerated whilst in the tank?

I have not changed the speed on the pump.

I'll keep you informed.

Thanks.

[Fred]

Hello,

I'm still hearing the occasional rush of bubbles. Like someone said, probably they are forced along the pipe when the pump starts and then they settle somewhere, though to me it sounds as thought they rise through the vent pipe.

I'm not aware on any leaks; that is to say there are no damp patches on the floors or ceilings. It would be very impractical to lift all the floorboards to check the entire pipe run, so what should I do next?

I see that Fernox do a leak stop solution. Should I add that and if it works, assume that I had a leak, or should I find the leak before treating it? How does it work anyway? I don't want it causing more trouble than it solves.

Thanks.

[Ed Sirett]

1) Check that the float valve works in the header tank. 2) Allow a few more days for the bubbles to settle out.