Gurgling and air in central heating

[jim843]

So, does this indicate to you so far, that the behaviour is the same as with the HW enabled, ie that the system will still "never" need top up no matter how much air is vented?. If this is the case, then that would indicate that you are pulling air into the system and not venting residual air. If the PHE was causing the problem then you would expect the overall boiler pressure to gradually decay? now that its (the PHE) out of the picture.

Yes, that’s my understanding. I haven’t topped the system up since…I don’t know when!

Is it safe to assume that we’re pulling in air BELOW the towel rail?

I can fairly easily cap off the top floor. And run the system and see if that stops air coming in.

I can cap off the middle floor, just leaving the ground floor, too - but obviously trickier as it’s winter and house will be cold.

Any other suggestions welcome!

 

[John.g]

I honestly don't know or even see how air can be getting in anywhere from outside, gases being generated inside the system would explain it but your hydrogen test was negative.

What about just shutting both isolation valves on that towel rail for a few days and see does air appear somewhere else?.

 

[jim843]

I honestly don't know or even see how air can be getting in anywhere from outside, gases being generated inside the system would explain it but your hydrogen test was negative.

What about just shutting both isolation valves on that towel rail for a few days and see does air appear somewhere else?.

I'll shut the towel rail off later in the week when the kids are away.

I fitted an automatic air vent from Aladdin on the towel rail. The last one didn't seem to work but this one definitely released air when I opened the valves on the towel rail again.

Just a few odd things I noticed when fitting it...

When closing the valves on the towel rail and opening the bleed valve, there was air for a few seconds and then water/air mix for a few seconds.

Hard to see but the water level was about an inch (why have I suddenly gone imperial!) below the top of the towel rail:

About this level:



And this is the muck inside the towel rail:

Is this considered dirty?

 

[John.g]

Rad looks very dirty, so would suggest another flushing out.

 

[jim843]

Rad looks very dirty, so would suggest another flushing out.

Ok. Will get someone in this time.

Could this be the cause of air?

 

[SJB060685]

The dirty water is a result of air ingress somewhere. The free oxygen is reacting with the iron content in radiators and causing corrosion, the result sludge build up. I know John disagrees with me but I'm still not convinced you don't have part of the system under negative pressure and drawing in air. The black iron oxide (sludge) is proving that.

 

[jim843]

The dirty water is a result of air ingress somewhere. The free oxygen is reacting with the iron content in radiators and causing corrosion, the result sludge build up. I know John disagrees with me but I'm still not convinced you don't have part of the system under negative pressure and drawing in air. The black iron oxide (sludge) is proving that.

Ok. So how do I diagnose this further?

Is it a matter of replacing pipe work?

 

[SJB060685]

I am pretty much convinced your problem is a pressure problem. Somewhere in the system under negative pressure is a weak point drawing in air, why it only accumulates in that one particular towl rail I can't answer. If the layout of the boiler John shared some time ago is correct then at least some of the system is under a negative pressure. If there's a weak point on this side that is below atmospheric pressure while the pump is running it will pull in air. Pressure is always trying to reach an equalibrium. I personally don't think how the boiler pipework and vessel location is laid out is correct but there must be somewhere with a weak joint, almost certainly on the suction side of the pump.

 

[jim843]

I am pretty much convinced your problem is a pressure problem. Somewhere in the system under negative pressure is a weak point drawing in air, why it only accumulates in that one particular towl rail I can't answer. If the layout of the boiler John shared some time ago is correct then at least some of the system is under a negative pressure. If there's a weak point on this side that is below atmospheric pressure while the pump is running it will pull in air. Pressure is always trying to reach an equalibrium. I personally don't think how the boiler pipework and vessel location is laid out is correct but there must be somewhere with a weak joint, almost certainly on the suction side of the pump.

By suction side do you mean the return side?

The pump is going, that’s positive?

The return is under negative?

I guess what I need is a method of how to isolate the problematic area. Is it likely to be a rad? A joint under the floor?

 

[jim843]

@SJB060685 you may be right. When the system was off over the summer there was no air in the rad. I’d wondered if air was accumulating and not being “pushed” into the rad by the pump?

 

[SJB060685]

Suction side is the inlet to pump. The discharge side (after the pump) should be under positive pressure, relative to pump ∆P (delta P).

If during summer use you accumulated no air then that would suggest as you say something somewhere is weak. You could go around tightening all connections above the floors, if the problem lies beneath floors that's a bit more of a problem.

 

[jim843]

Suction side is the inlet to pump. The discharge side (after the pump) should be under positive pressure, relative to pump ∆P (delta P).

If during summer use you accumulated no air then that would suggest as you say something somewhere is weak. You could go around tightening all connections above the floors, if the problem lies beneath floors that's a bit more of a problem.

Really hard to say, there was a tiny bit of air over the summer (a tiny spurt and then water) but not this much. I’m bleeding every day for between 3 and 10 secs.

I did notice this on one of the rads:


This rad is very rarely on as the room gets warm during the day and is cool at night.

Could this be a cause?

 

[John.g]

Would definitely prefer to see the EV installed on the pump suction side like this Vokera Combi but there must be thousands of Baxis with them on the discharge side.

 

[SJB060685]

That rad lockshield looks like it's been bombarded with PTFE on the return, possibly because of a leak on the old system under positive pressure and could quite well be the culprit. I would consider remaking that joint. Where is that rad in relation to the towl rail?

 

[SJB060685]

Would definitely prefer to see the EV installed on the pump suction side like this Vokera Combi but there must be thousands of Baxis with them on the discharge side.

View attachment 65231

Many systems would work like that if air tight but not if there's a weak point.

 

[jim843]

That rad lockshield looks like it's been bombarded with PTFE on the return, possibly because of a leak on the old system under positive pressure and could quite well be the culprit. I would consider remaking that joint. Where is that rad in relation to the towl rail?

This is on the same floor, about 8m away.

What would you recommend when redoing the joint? How many winds of PTFE?

As this rad is almost always off I could always just cap off the pipe work for a few days and see if that resolves?

I’m not adverse to doing this myself but I must admit I don’t like it. I fit an 8000 BTU rad in the kitchen and hated every minute of it!

 

[SJB060685]

Ok. Close both valves for a day or two and see if it draws in air. I'm willing to bet based on the state of that lockshield and the crude attempts to fix an obvious problem that no air will be drawn in to the towel rail. If this proves correct you would need to remake that joint. You shouldn't need any PTFE or jointing compound on a valve if holding true.

 

[John.g]

With EV on the pump discharge, the way I see it is that the pressure at any point in the system will be reduced by the pump head so presumably a severe restriction can allow air ingress at a weak point(s).

 

[jim843]

Ok. Close both valves for a day or two and see if it draws in air. I'm willing to bet based on the state of that lockshield and the crude attempts to fix an obvious problem that no air will be drawn in to the towel rail. If this proves correct you would need to remake that joint. You shouldn't need any PTFE or jointing compound on a valve if holding true.

ok, will try.

here is my attempt at fitting the rad in the kitchen.


there is some blue staining underneath the TRV bit and also on the pipe coming out the wall. The thing is, when the floor is mopped this pipe can get wet. That would cause the blue staining?

I put loads of PTFE on this rad because the lad that fit two other rads in the house for about £300 said you need 25 turns of PTFE on these acova rads?

 

[SJB060685]

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.

 

[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.