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?