Air getting into system

[Roger465]

So every so often I hear a gurgle from the kitchen, and air gets into the rad. Every few days, I bleed it to let the air out. It’s what I think you call a vented system? Little header tank in the attic.

Anyway, I’m assuming that, if air gets in, by the laws of physics water is getting out. Somewhere. The pipework is under the concrete floors… I assume there’s a leak down there somewhere, but I’m not planning to dig all my floors up to find out… am I right to think this, or are there any other possibilities? There isn't any water getting out anywhere in the house…

Then the other thing which occurred to me is (and you can tell I know nothing about heating) doesn't the system have anti-corrosive stuff in it, which will dilute more and more every time I bleed the system?

What should I do please?

Thanks

 

[Harry Bloomfield]

It could be air drawn in via the expansion pipe, due to pump running too fast or the expansion pipe wrongly located in the pipework - rather than any loss of water. The expansion pipe runs up to your header tank, but rises above it then drops down, so if there is any over spill of expanded water, it flows back into the tank.

It can take months of bleeding, to get all of the air out of a system.

 

[Roger465]

Don't know if anybody's looking at this, but do you think I should tip some Fernox or something into the header tank every so often...?

Thanks

 

[Harry Bloomfield]

Don't know if anybody's looking at this, but do you think I should tip some Fernox or something into the header tank every so often...?

Thanks

Pointless adding Fernox, unless there is an actual leak. The actual amount of Fernox compared to the water volume in a typical system is relatively small, so it would need to be substantial leak to need topping up frequently.

 

[Roger465]

Thanks Harry – well, the rad in the kitchen gets half full of air every couple of weeks or so. I’m not very knowledgeable when it comes to such matters, but that seems like a lot.

I didn’t really understand what you said about air getting in via the overflow… I suppose I’m thinking, simplistically, if a lot of air’s getting into the rad, the displaced water must be going somewhere.

Is the overflow simply an open pipe connected to the rads, which allows water to vent up into the header tank in the attic when it gets hot and expands or something?

And then, can air get drawn back in through the overflow pipe, all the way back down into the system again? Sorry, I’m just trying to visualise it and get some idea how it all fits together.

If it’s any help, I frequently hear gurgling in the kitchen rad shortly after turning the heating on – presumably that’s it getting air pumped into it somehow.

The kitchen rad isn't the one closest to the boiler/pump, if that’s relevant – however, the two which are closest are permanently turned off as I don’t use that room…

 

[Harry Bloomfield]

Is the overflow simply an open pipe connected to the rads, which allows water to vent up into the header tank in the attic when it gets hot and expands or something?

Basically, yes! If the overflow/vent pipe is badly located, or the pump speed is too high, air can be sucked down that pipe. Try reducing the pump speed, see if that makes a difference.

If that is the case, the water level will rise in the header tank and maybe it will expel it via the overflow. Any sign of it overflowing outside?

Another possibility is gas being generated by the internal rusting of the radiators. Is the water when you bleed it clear or discoloured, is there a smell from the air which escapes?

 

[Roger465]

Basically, yes! If the overflow/vent pipe is badly located, or the pump speed is too high, air can be sucked down that pipe. Try reducing the pump speed, see if that makes a difference.

OK – will do

If that is the case, the water level will rise in the header tank and maybe it will expel it via the overflow. Any sign of it overflowing outside?

Don’t THINK so…

Another possibility is gas being generated by the internal rusting of the radiators. Is the water when you bleed it clear or discoloured, is there a smell from the air which escapes?

Seems quite clear – and I know the smell you mean, from previous houses, but no, not much smell here…

 

[ScottishGasMan]

Firstly I would suggest testing if it is air getting into the system, or if it is hydrogen gas being produced in the system as a byproduct of corrosion in the system.

Easy test. Get a small container with a narrowish end like a small juice bottle or preferably something that shape/size but a bit more sturdy, open the bleed point and hold the container upside down over it and try get the vented gas into the container, close bleed point and quickly take a match or lighter to the end of the container now being held sideways or with the open end pointing slightly up. If its hydrogen it should light with a very significant and quick pop/woosh noise, if its air, nothing will happen.

 

[Alec_t]

A while back I had a similar problem with air getting into the system. I put up with it for some time, then had occasion to replace a three-port CH/HW selector valve which had been weeping at the drive shaft bearing unknown to me because the leakage rate equalled the evaporation rate, so no drips. New valve, no more gurgling since. So presumably the air had been drawn in at the point of the leak.

 

[Mottie]

I used to get a fizzing/gurgling in my sealed system and a small amount in one of my rads. After a recommendation from muggles on here, I fitted a Spirovent RV2 to my system. Completely cured it.

 

[ScottishGasMan]

I used to get a fizzing/gurgling in my sealed system and a small amount in one of my rads. After a recommendation from muggles on here, I fitted a Spirovent RV2 to my system. Completely cured it.

The spirovents are great bits of kit,

 

[Roger465]

A while back I had a similar problem with air getting into the system. I put up with it for some time, then had occasion to replace a three-port CH/HW selector valve which had been weeping at the drive shaft bearing unknown to me because the leakage rate equalled the evaporation rate, so no drips. New valve, no more gurgling since. So presumably the air had been drawn in at the point of the leak.

Cheers... I mean, something like that would be well beyond me I think... but that sounds like it would be a very slow, steady ingress of a small amount of air? What happens with mine is that, some time not too long after the heating comes on with the timer, I hear a great big gurgle in the kitchen, which means a lot of air in the rad.

I *think* that suggests that a slow, steady leak might be unlikely...

I'll Google that Spirovent thingy

 

[Roger465]

If its hydrogen it should light with a very significant and quick pop/woosh noise, if its air, nothing will happen.

I was known* as the phantom bomb-maker of he posh school in which I was misplaced, back in the 60's - I studied pyrotechnics and how to use small quantities of exotic explosives to terrify (but not injure) bullying teachers. My favourite was nitrogen tri-iodide, which could be painted on door knobs etc, and would explode when someone grasped the handle, giving a mild burn and a massive cloud of purple smoke.

Back on topic, the reason I mention it was that the first ever explosion which fired my imagination in chemistry class was hydrogen - described by the teacher as a "squeaky pop" - a bit like a musical fart

I'll try it and report back...

*More accurately, I was NOT known - until long after I left school...

 

[Roger465]

Try reducing the pump speed, see if that makes a difference.

OK... so it's been a couple of weeks now, and there's been a lot less gurgling - and there's still some air getting into the kitchen rad, but nowhere near as much. In fact, I was just about to pronounce it cured when I heard a little gurgle form the kitchen, and it's let a little in.

But it's definitely better... I turned the pump down from full on to this - what shoudl it be set at, anyway? Currently half the rads in the house are turned off, so it's running... ummm... 7 or 8.

 

[Harry Bloomfield]

OK... so it's been a couple of weeks now, and there's been a lot less gurgling - and there's still some air getting into the kitchen rad, but nowhere near as much. In fact, I was just about to pronounce it cured when I heard a little gurgle form the kitchen, and it's let a little in.

It could just be air already in the system, finding the high spots to collect. It can take months to completely bleed all the air out of a system.