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Gurgling and air in central heating

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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?
 
Looks like that but really you shouldn't be getting any air anywhere now IF that is/was the problem, did you or someone say that air might be getting in where the electric heating element is screwed into it?, you might be able to rejoint that.

I said there is a T piece with an electric element. I wondered if the rubber seals could be letting air in?

IMG_9177.jpg
 
Could be corrosion cheap towel rads are know for it
 
Well, I like the fact that you're working on ruling that out, I suppose. They could be a weak point, and if the towel rail is running under negative pressure (which the jury is still out on) they could be the point of entry.

I’m not sure how the rad is running under negative pressure?

I do know that if I isolate the towel rail and bleed it for a while it seems to be full of air. If I bleed I’ll get a blast of air, then water, then air. It’ll gurgle and finally lose pressure and the water level in the rad is way below the top of the rad.

If this rad was drawing in air or rusting, surely it would do the same while isolated and running on the electric element?

Happy to replace it but would like to rule it out. The pipes are in the wall so a replacement would mean a bit of smashing out. Would rather avoid if unnecessary.
 
The towel rail will not be running negative while isolated (assuming you are isolating both sides...?). If the pressure is only negative at certain times (could happen only on pump start up), it might be hard to see the negative pressure. I'm not entirely convinced the towel rail IS under negative pressure, though, so that's why I like the fact that you are testing it!
 
Happy New Year all!

I didn't get around to replacing the towel rail before Christmas. The towel rail was rapidly filling with air. About 1 bar on the towel rail each day would become cold. I added a couple bottles of inhibitor to the towel radiator as I was concerned that the system was running low.

I got Baxi out and the engineer gave yet another opinion! He said that air in the system would take years to work its way out of the system. I was a bit suspicious as I've never heard this before. He said let the air fill up, bleed it in a few months, don't worry about it, there's no leak.

Anyway, in the run up to New Year about half the towel rail was cold.

At 7am on New Year's Day, I noticed water on a bedroom ceiling. I went into the loft, opened the hatch in the dwarf wall and could see that a speedfit elbow had leaked.

Now, the pipework above behind the dwarf wall was probably the height of the radiator in the loft. What I mean is that this is the highest pipework in the house, nearly level with the top of the radiator. I trimmed the speedfit down a bit so it's roughly level with the bottom of the radiator and replaced the elbow.

Since then the towel rail has been red-hot. I've heard no gurgling. It's been six days.

Could it be that this elbow at the top of the house was somehow pulling in air?
 
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