Gurgling and air in central heating

[jim843]

The rads closest to the boiler and at lower points in the system should be under positive pressure and a weak point would be recognised as a drip. Any points higher in the system and weak could well be under negative pressure.

OK. That is useful.

Any rad above the ground floor could be a culprit.

The towel rad also has an electric heating element that (I believe) only has a rubber seal on. There’s a T piece where the CH system connects in.

I guess I can go around switching off each rad for a day or two. If the air stops, I know it’s the rad that is off.

 

[jim843]

The rads closest to the boiler and at lower points in the system should be under positive pressure and a weak point would be recognised as a drip. Any points higher in the system and weak could well be under negative pressure.

Just thinking about this…

Any other rad in the house spits out water instantly. This means they’re under positive pressure (water being forced out).

If the rads on the second and third floor were under negative pressure I’m guessing opening a bleed valve would cause air to be sucked in?

If so, this ain’t the case. When I open them to bleed there is only water coming out.

 

[SJB060685]

That depends. If you're bleeding the rads with the boiler and pump off then you will get water come out. If bleeding with them on then you should draw air in if under negative pressure.

 

[jim843]

That depends. If you're bleeding the rads with the boiler and pump off then you will get water come out. If bleeding with them on then you should draw air in if under negative pressure.

Ok. So if the heating is on I can test if there’s negative pressure if any of the rads. I can do this as well.

I’m just keen on verifying the problem before I start replacing pipe work!

 

[John.g]

My thinking on this, especially in view of the above ongoing air ingress is that negative pressure is NOT required, and that with any slight leak, even a weep, that air finds it far easier to gain access than for the water to seep out?. Maybe not quite alalogous to oxygen gaining access through "solid" plastic (non barrier) piping, who would have believed that but it does happen.

There was a good post on here a few years ago from someone (plumber) who had experience of two houses, one sealed, the other OV, where both had lengths of non barrier piping, the sealed one kept getting air problems but the OV one didn't, he put this down to the fact that the OV one could constantly vent any air continuously through its 22mm vent.
I think I may have a few lengths of non barrier piping in my loft area which has two rads but again never ever get air problems probably because of the OV system?.

Actually, both these rads run with a very very slight negative pressure at the vents but because the whole system is drop tight ( I installed it !) then no problems.

 

[jim843]

My thinking on this, especially in view of the above ongoing air ingress is that negative pressure is NOT required, and that with any slight leak, even a weep, that air finds it far easier to gain access than for the water to seep out?. Maybe not quite alalogous to oxygen gaining access through "solid" plastic (non barrier) piping, who would have believed that but it does happen.

There was a good post on here a few years ago from someone (plumber) who had experience of two houses, one sealed, the other OV, where both had lengths of non barrier piping, the sealed one kept getting air problems but the OV one didn't, he put this down to the fact that the OV one could constantly vent any air continuously through its 22mm vent.
I think I may have a few lengths of non barrier piping in my loft area which has two rads but again never ever get air problems probably because of the OV system?.

So this means the problem could be anywhere, right?

I’ll do what I can do find the problem but short of ripping out pipe work on 3 floors I may never find it.

If the auto air vents work on the towel rail, is this equivalent to an OV system? At least air makes it’s way out of the system?

 

[John.g]

Yes, I think it could be, but if you fix the obvious ones and give the system a thorough cleaning then would think that you will be OK.
I wouldn't compare auto vents with a OV as the auto vent tends to operate more on/off and I certainly wouldn't dream of using them as a cure by installing them on all rads, maybe OK on your towel rad as a temporary measure, remember there was a magic Aladdin lamp but not ditto for Aladdin's auto air vents.

 

[SJB060685]

Can I just say that you have mentioned replacing lots of pipework at least twice and I have never agreed with you, I am not suggesting that. If air is being drawn in then it will be coming from a weak fitting somewhere

 

[jim843]

Can I just say that you have mentioned replacing lots of pipework at least twice and I have never agreed with you, I am not suggesting that. If air is being drawn in then it will be coming from a weak fitting somewhere

ok, so in your opinion it’s a weak fitting. That’s a relief somewhat!

I guess I’m going to “worst case“ scenario which is lift up floorboards and smash out a couple walls!

I may try and find a local heating engineer to do this. I’ve struggled in the past to find anyone reputable.

 

[jim843]

@SJB060685 haven’t had much luck getting an engineer along.

Spoke to a bloke this afternoon who said I’ve either got a leak or the cold water supply is somehow feeding into the system. I said I removed the filling loop and he suggested that the cold water supply is somehow piped into the heating. I don’t see how this is possible!

I need to isolate a couple rads this week to see if they are the source of the problem.