Gurgling and air in central heating

[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.