Gurgling and air in central heating

SJB060685 · Oct 18, 2021

If there was a weak point in the system at low pressure you would draw in air yes.
The expansion vessel will be positioned before the pump, with the pump pumping away. The point the vessel connects to the system is the neutral point or point of no pressure change. Between the vessel and pump will be a very short section of pipework under negative pressure, the pump will then add it's differential pressure to the discharge side, this will supply a positive pressure throughout the system back to the point of no pressure change at the vessel connection point.

Deleted member 123817 · Oct 18, 2021

Pressure won't drop with a leak if the filling loop has a PRV with the isolation valve open, so called auto filling.

SJB060685 · Oct 18, 2021

johntheo said:
Pressure won't drop with a leak if the filling loop has a PRV with the isolation valve open, so called auto filling.

A crude means of auto top up yes but if there was a leak I'm sure he would of noticed somewhere, that would be a lot of fresh water being added to the system.

jim843 · Oct 18, 2021

SJB060685 said:
If there was a weak point in the system at low pressure you would draw in air yes.
The expansion vessel will be positioned before the pump, with the pump pumping away. The point the vessel connects to the system is the neutral point or point of no pressure change. Between the vessel and pump will be a very short section of pipework under negative pressure, the pump will then add it's differential pressure to the discharge side, this will supply a positive pressure throughout the system back to the point of no pressure change at the vessel connection point.

Yeah, so if the system is at less than 1 bar and there's a weak point, air would be pulled in.

SJB060685 said:
A crude means of auto top up yes but if there was a leak I'm sure he would of noticed somewhere, that would be a lot of fresh water being added to the system.

Isolation valve is a manual turn on/off thingy.

As far as I can tell there is no pressure drop based on the gauge.

Conversely, if air is being generated in the system, shouldn't I see a pressure increase on the gauge?

SJB060685 · Oct 18, 2021

If you read .5 bar on the pressure gauge at the boiler then the pressure at the highest point of the system will be less, perhaps no water up there at all and yes air can enter.
Would air being admitted into the system cause the pressure to rise? Yes it would.

jim843 · Oct 18, 2021

SJB060685 said:
If you read .5 bar on the pressure gauge at the boiler then the pressure at the highest point of the system will be less, perhaps no water up there at all and yes air can enter.
Would air being admitted into the system cause the pressure to rise? Yes it would.

Pressure is now between 2.2 and 2.5 (I've not seen it drop below 2.2).

There's defo water in the rads at the top of the house.

When I pressurised to a higher bar I got the tado app to open all valves so everything was open. I only forgot about the two rads in the house in the hall that have normal TRVs.

jim843 · Oct 18, 2021

SJB060685 said:
Would air being admitted into the system cause the pressure to rise? Yes it would.

So the pressure never seems to drop or rise over time.

That said, I haven't looked too much at the gauge going up as I have been looking for drops and bleeding the bathroom rad.

SJB060685 · Oct 18, 2021

2.2 bar cold?

jim843 · Oct 18, 2021

SJB060685 said:
2.2 bar cold?

Not stone cold, cool-ish. Because the heating has been on because of cold weather it's never quite cold.

As an example, when the pump comes on the pressure drops to about 2 bar. When the pump switches off, it goes to 2.2 or slightly higher.

Based on what @johntheo said I checked the flow and return pipes...

Facing the boiler, the left most pipe seems to be the flow. The filling loop goes from the cold water supply to the return. The return has the magnetic filter on.

I checked the schematics in the installation and service manual and this seems to match.

Deleted member 123817 · Oct 18, 2021

How often have had to top it iup?

jim843 · Oct 18, 2021

johntheo said:
How often have had to top it iup?

Never.

I bleed the air. That’s it.

Deleted member 123817 · Oct 18, 2021

So after bleeding the air off each time the pressure returns to normal ?. I know it doesn't add up but could/can you remove the filling loop to absolutely rule it out.

jim843 · Oct 18, 2021

johntheo said:
So after bleeding the air off each time the pressure returns to normal ?. I know it doesn't add up but could/can you remove the filling loop to absolutely rule it out.

I’m not sure that the pressure rises. I will try and monitor.

It’s hard because it fluctuates a little bit. Baxi engineers said this is normal.

Not sure how to remove the filling loop exactly. Would I have to drain the system?

Deleted member 123817 · Oct 18, 2021

There should be a flexible hose somewhere where it connects to the boiler return with isolating valves or can you post a photo of the isolation valve you described previously?

Do mean by PG fluctuations that it changes fairly rapidly while watching it and have you watched it for any unusual behaviour while using hot water?

jim843 · Oct 18, 2021

johntheo said:
There should be a flexible hose somewhere where it connects to the boiler return with isolating valves or can you post a photo of the isolation valve you described previously?

Do mean by PG fluctuations that it changes fairly rapidly while watching it and have you watched it for any unusual behaviour while using hot water?

Will see if there are isolating valves behind.

The pressure only drops/rises when the pump goes on/off. Not during heating.

Haven’t checked when using hot water but will check tomorrow.

jim843 · Oct 18, 2021

@johntheo while I was looking I noticed this.

Also some of the copper pipes into the boiler have this.

Anything to worry about?

John.g · Oct 18, 2021

jim843 said:
Will see if there are isolating valves behind.

The pressure only drops/rises when the pump goes on/off. Not during heating.

Haven’t checked when using hot water but will check tomorrow.

That is the filling loop with a non return valve where shown and a isolating valve where shown on the other end, ensure the isolation valve is closed "across (at right angles to) the pipe" then just slacken the flexible hose where attached to the NR valve but do not remove it, when slackened a few turns water should only dribble out for a few seconds and then stop.
There may be another isolation valve on top of the NR valve but I don't think so, if there is, shut it as well

John.g · Oct 18, 2021

jim843 said:
@johntheo while I was looking I noticed this.

Also some of the copper pipes into the boiler have this.

Anything to worry about?

I dont't think so, these look like isolating valves for the boiler flow/return.

jim843 · Oct 18, 2021

John.g said:
That is the filling loop with a non return valve where shown and a isolating valve where shown on the other end, ensure the isolation valve is closed "across (at right angles to) the pipe" then just slacken the flexible hose where attached to the NR valve but do not remove it, when slackened a few turns water should only dribble out for a few seconds and then stop.
There may be another isolation valve on top of the NR valve but I don't think so, if there is, shut it as well

Ok, I’ll try this tomorrow along with the hydrogen check!

Do you think air could be somehow being pulled into the system here?

If so, would it be the loop or the NRV?

John.g · Oct 18, 2021

No, I think it highly unlikely because even if the flexible hose is perished/holed then with a sealed system the pressure should still keep the NR valve shut. I also find it difficult to imagine that you are pulling in air anywhere in the volumes that you are getting especially if the boiler pressure is normally 1bar or higher. Lets hope in one way that its hydrogen!.

jim843 · Oct 18, 2021

John.g said:
No, I think it highly unlikely because even if the flexible hose is perished/holed then with a sealed system the pressure should still keep the NR valve shut. I also find it difficult to imagine that you are pulling in air anywhere in the volumes that you are getting especially if the boiler pressure is normally 1bar or higher. Lets hope in one way that its hydrogen!.

I’ll take a video of the amount of air/hydrogen coming out so it’s easier to see.

Is it worth doing the bleed when the system is cold? And by cold, how long should the system be off for?

John.g · Oct 18, 2021

I've only had to vent some air from my open vented system after a complete drain down and refill, I would stop the circ pump/boiler and then vent when hot. Hot or/& cold better IMO to vent with pump off.

jim843 · Oct 22, 2021

I vented the bathroom towel rail today. Heating was turned off. System was still a bit warm.

I got about 7 seconds worth of air with a quarter turn of the bleed valve.

Here is the pressure before bleeding:

And pressure after bleeding:

Thing is, the pressure gauge usually varies a bit.

From earlier in the week:

@jim843 I tried the hydrogen test. There was no pop.

@John.g do you still think it's worth removing the filling loop?

@johntheo I turned on the hot water and the pressure does drop. It went from about 2.4 to about 2. Is this a problem?

Thank you all for your help. It's been very useful for me to vent (no pun intended?!) and discuss this.

John.g · Oct 22, 2021

Yes, definitely remove (after first slackening) that filling loop, it's only hand tightened at the connection to the NRV, obviously ensure that the isolaton valve is shut, as it appears to be, then post back.

jim843 · Oct 22, 2021

John.g said:
Yes, definitely remove (after first slackening) that filling loop, it's only hand tightened at the connection to the NRV, obviously ensure that the isolaton valve is shut, as it appears to be, then post back.

Ok. Just so I'm clear, remove loop and leave it a couple days and see if there's any air in the system?

Gurgling and air in central heating

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