Gurgling and air in central heating

SJB060685 · Oct 26, 2021

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 · Oct 26, 2021

SJB060685 said:
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 · Oct 26, 2021

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 · Oct 26, 2021

SJB060685 said:
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 · Oct 26, 2021

@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 · Oct 26, 2021

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 · Oct 26, 2021

SJB060685 said:
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 · Oct 26, 2021

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 · Oct 26, 2021

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 · Oct 26, 2021

John.g said:
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 · Oct 26, 2021

SJB060685 said:
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 · Oct 26, 2021

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 · Oct 26, 2021

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 · Oct 26, 2021

SJB060685 said:
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 · Oct 26, 2021

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 · Oct 26, 2021

SJB060685 said:
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 · Oct 26, 2021

SJB060685 said:
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 · Oct 27, 2021

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 · Oct 27, 2021

SJB060685 said:
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 · Oct 27, 2021

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 · Oct 27, 2021

John.g said:
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 · Oct 27, 2021

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 · Oct 27, 2021

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 · Oct 27, 2021

SJB060685 said:
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 · Nov 2, 2021

@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.

jim843 · Nov 2, 2021

@SJB060685 and @John.g struggling to find the time (or a heating engineer!) to deal with the system.

There is a new sound today, though: a whistle/whine from the boiler!

HW was running at the time.

John.g · Nov 2, 2021

Presume there was no noise before with DHW on?. Can you shut down the boiler and just open the same "hot" tap the same amount and see if noise is gone, this may at least prove that the noise is from the primary side.

jim843 · Nov 2, 2021

John.g said:
Presume there was no noise before with DHW on?. Can you shut down the boiler and just open the same "hot" tap the same amount and see if noise is gone, this may at least prove that the noise is from the primary side.

What do you mean by shut down? CH off and HW Only?

John.g · Nov 2, 2021

Shut off both CH & HW (or switch off the boiler completely) and open the hot tap, this will just run cold water (now) through the combi and see if noise is gone.

jim843 · Nov 6, 2021

John.g said:
Shut off both CH & HW (or switch off the boiler completely) and open the hot tap, this will just run cold water (now) through the combi and see if noise is gone.

@John.g sorry for the delay.

I ran the hot water with everything on. There was the whistling noise.

While the water was running, I switched the boiler off entirely. The whistling sound was still there.

What does this mean?

Deleted member 123817 · Nov 6, 2021

If you were still running the cold water through the combi (hot water tap open) tht em the whistling is caused by this and not the primary water (dirty water).
So don't really know what it means in the context of air in your rads etc.

Can't post on my Windows10 laptop for some reason or other.

John.g · Nov 6, 2021

johntheo said:
If you were still running the cold water through the combi (hot water tap open) tht em the whistling is caused by this and not the primary water (dirty water).
So don't really know what it means in the context of air in your rads etc.

Can't post on my Windows10 laptop for some reason or other.

Have you blanked off that leaking non return valve.

Also just to be sure (again) did you say that with the boiler (&circ pump) ON that you are getting water out of all the rad vents apart from towel rail which emits air initially, does the towel rail also emit water eventually with the boiler/circ pump on?.

jim843 · Nov 7, 2021

John.g said:
Have you blanked off that leaking non return valve.

Also just to be sure (again) did you say that with the boiler (&circ pump) ON that you are getting water out of all the rad vents apart from towel rail which emits air initially, does the towel rail also emit water eventually with the boiler/circ pump on?.

@John.g I got a new filling loop and attached one of the isolation switches like this:

When I removed the old filling loop it still had some water in despite not being used for weeks (if not months).

I then switched on the CH system and went round all 9 rads in the house.

Every rad bled water apart from two. The rad in my son's room bled a little air, then water. The towel rail in the bathroom bled quite a bit of air (as usual) and then bled water.

John.g · Nov 7, 2021

Can shut off that towel rad "permanently" for a few days and see does the air appear somewhere else and if noise subsides?.

jim843 · Nov 7, 2021

John.g said:
Can shut off that towel rad "permanently" for a few days and see does the air appear somewhere else and if noise subsides?.

I can but we had the same problem before this towel rail was installed. The air just appeared in one of the top floor rads.

I haven’t heard the gurgling for a while now. Just air.

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