Gurgling and air in central heating

[jim843]

Hello,

Around 2 years ago we had a very old, leaky Baxi combi replaced with a newer Baxi.

For background I live in a 3 storey terrace. First floor has 3 rads, second floor has 4 rads and third floor has 2 rads.

We noticed problems with noise and air in the system. One of the rads in the loft made gurgling noises. If the rad was bled, air came out. Also, at this time the pressure gauge was all over the place. Up to 3, back down to 1 and every number in between. The gauge didn’t appear to drop, though.

The installer wasn’t helpful over the phone so I ended up finding a different engineer.

Turns out the installer of the boiler didn’t do a particularly thorough job. He didn’t clean the old system, I found leaks on some of the nuts beneath the boiler, he didn’t fit a soak away outside so water drips out over our path (great in winter when it’s freezing).

He engineer found the expansion vessel was flat. He pumped it up, tightened the pipes, advised on a soak away. He told me to bleed all the rads individually for a few mins, top up the system and add more inhibitor. He also suggested power flushing the system. I did all this and also rented a machine and flushed the system myself.

I did all this but the problems remained. I ended up contacting Baxi who came out and replaced the expansion vessel.

This didn’t solve anything. More gurgling, more air.

We ended up getting the boiler serviced again (this is maybe a year after install) and I mentioned the problems to the engineer. He asked the usual questions (is there inhibitor, have you bled the system, etc) and mentioned we had an old radiator in the bathroom. He thought this might be the source of air.

We were planning on getting the bathroom refitted so I decided to wait and see if that solved any issues.

We got the bathroom refitted. Now, the gurgling and air does not go to the top of the house but is in the towel rail in the bathroom. I can bleed the rad once a day and there’s maybe a second or two of air and then water. The pressure does not drop on the boiler.

I contacted Baxi again who came out and replaced the expansion vessel with a bigger one. The engineer also suggested fitting an automatic bleed valve on the chrome towel rail because in his experience chrome towel rails suck in air. I bought one two valves (one for spare) and fitted it.

I noticed an odd thing while fitting the automatic bleed valve. I turned off the two rad valves, released the pressure. Once the air left the rad I could put my finger in the top of the rad and feel there was no water there at all. I’d expected that the water would be just below the top of the rad?

But you’ve guessed it — still gurgling and air in the system! The automatic bleed valve doesn’t appear to vent automatically, not sure why. Could be faulty. I can swap it over with the spare but haven’t gotten around to it yet.

The only other thing I noticed with the system is that if the system is off in the summer then there is minimal air in the rad. I assume because the pump isn't forcing water around the system?

If you got this far, thanks! I’d love to solve this issue and have a system that works! I’m not opposed to ripping out pipework and starting again (even though I’m nearing the end of a long renovation!). Ideally there are some simpler steps I can take to diagnose?

Any advice?

 

[SJB060685]

That's a bit of a length post . When the system is cold what are you pressurising the system to?

 

[Last Plumber]

Whopper of a post!
I don't agree with the auto air vent idea. A heating system should not be producing or introducing gases. Once they are installed correctly they shouldn't really need 'topping up'.

How far vertically (feet or meters) is the top of the top rad/towel rail from the bottom of the boiler?
What pressure is in the boiler when it is cold and not running?
Just for information.

 

[jim843]

Thanks, both! I went for maximum detail!

From bottom of boiler to top of towel rail it’s about 3.6m. There’s another floor above as well.

Pressure from cold? Not too sure now as it hasn’t been refilled in ages.

I know that when the pump stops the gauge hovers around 1.5. When the pump comes on it’ll drop to about 1.2. There’s a slight variance.

 

[SJB060685]

When filling a pressurised system you have allow for the lift/height of the property. So if the boiler and pressure gauge are on the ground floor and the highest pipework above it is say 5m then you will have to fill to at least .5 bar plus a bit extra so the pipes at the highest point of the system don't draw/suck in air.

 

[jim843]

@SJB060685 thanks. I’ll let the system cool and pressurise to say, 2.2? If that number seems reasonable I’ll go ahead and do it.

Out of interest, why would air collect in the bathroom towel rail and not the two rads on the floor above?

 

[SJB060685]

@SJB060685 thanks. I’ll let the system cool and pressurise to say, 2.2? If that number seems reasonable I’ll go ahead and do it.

Out of interest, why would air collect in the bathroom towel rail and not the two rads on the floor above?

When the system is cold top up to about 1.5 bar and see if that has an affect. I wouldn't go as high as 2 bar as this is likely to cause the prv to discharge when the system is hot, the vessel condition and charge will have an affect on system pressure as well.
Why would air settle in the towel rails and not on the floor above? Air is less dense than water so you are correct to assume that it would settle at highest point of the system and usually does, however by design towel rails are taller and it's possible the air is getting stuck at the top and the water is circulating below it, happy to be proved wrong there though?

 

[Deleted member 123817]

Check that the flow/return piping are connected correctly to the boiler ie not reversed , would normally expect pressure to rise when the circ pump starts,

 

[jim843]

Check that the flow/return piping are connected correctly to the boiler ie not reversed , would normally expect pressure to rise when the circ pump starts

Gotcha.

I was under the impression that the flow and return didn’t matter? Like, doesn’t matter which way the flow and return is attached to bidirectional TRVs, etc?

I think I’m missing something!

 

[jim843]

Check that the flow/return piping are connected correctly to the boiler ie not reversed , would normally expect pressure to rise when the circ pump starts,

Or if I ask another way: how can I tell if the flow and return and round the wrong way?

All I can see is some pipe work going from the boiler. I don’t know which should be the flow, which should be the return…