Always lots of air in our CH system

[Richtop8]

When I turn on our CH there's a lot of noise from one specific part of the system - the pipes on the landing, and one radiator. It sounds like air, and the landing radiator needs bleeding regularly (about once a month), even though it isn't the highest point in the system. The two upright rads in the bathrooms are a good 50cm higher but rarely have more than a quick "pfffft" of air if I open the bleed valves. All the radiators get hot from top to bottom (except when the landing one needs bleeding) and the noise stops after a couple of minutes running.

Wondering what could be causing one radiator to fill with air so quickly, and why there could be so much air trapped in one part of the system. I can't see any sign of a leak. Any ideas?

 

[John.g]

Have you a sealed or open vented system?

 

[Richtop8]

Have you a sealed or open vented system?

You'll have to forgive me - I'm not great with the terminology - but I think it's vented. There's a dome-shaped air separator at the highest point in the airing cupboard, out of the top of which comes a pipe that goes all the way to the header tank where it curves over the tank. The system was installed around 1990, although the boiler has been replaced within the last ten years. When the boiler was changed a Valiant magnetic filter was added, and this has been drained a few times.

 

[John.g]

You might post a photo of that, it sometimes gets full of sludge causing those problems you are getting, if your boiler is a heat only boiler it will have a circulating pump installed close to this and after it, the boiler would be the "4" series like a 418 or 424 etc, if so post a photo of this pump as well.

 

[Richtop8]

This is the boiler. It was installed about eight years ago. It's been maintained pretty well and has a magnetic filter installed above it.

This is the separator in the airing cupboard. I used a very powerful magnet to try and dislodge anything clogging it up. The magnet did something because you could hear stuff moving and going down the pipe when it was released. I did this a few times until there was no more sound when it was taken off.

This is the pump. It’s below the separator (about 20cm). Between the separator and pump is the feed which comes down from the header tank. The pump was changed when the boiler was installed, so is also about eight years old.

 

[John.g]

Try and look into the small feed and expansion tank in the Attic and see if water is flowing out of the vent pipe or drawing air into it, you will have to hold a "glass" full of water with the vent pipe immersed in it to see this. If neither, get someone to start the boiler and see if any spurt of water from the vent, then get them to stop the pump and watch again for any spurt of water, you may have to wait for ~ 3 minutes for the pump to stop after boiler switch off.

How may rads have you got?

 

[Richtop8]

Try and look into the small feed and expansion tank in the Attic and see if water is flowing out of the vent pipe or drawing air into it, you will have to hold a "glass" full of water with the vent pipe immersed in it to see this. If neither, get someone to start the boiler and see if any spurt of water from the vent, then get them to stop the pump and watch again for any spurt of water, you may have to wait for ~ 3 minutes for the pump to stop after boiler switch off.

How may rads have you got?

I'll give that a try.

Sixteen rads. Two have never worked. We had the system power flushed when the boiler was fitted, and we were told this would sort it, but it didn't. One is in the hall and the other is a small secondary rad in the living room, so it's never been a big deal, but there are problems somewhere.

I go around with the key a few times a year, but most rads have no air or just a tiny bit. It's only the one noisy rad that seems to fill with air, but thinking about it, that might be the first one the pipes go to. It's the closest to the air separator/pump.

The pipework to the rads is microbore. Does that make them more likely to block with crud? I assume it does.

 

[gmartine]

If you're prepared to flush the system you could leave some system cleaner in there for a few weeks while the CH is on and see it that unblocks anything. I'll leave John to advise about the F/E tank and pump but I'd seriously consider getting the system sealed, it does save alot of ball ache with air ingress.

 

[Timmy D]

Pump prob set to high and could be drawing air down the vent.

 

[Bev GG]

I had a similar problem, air building up in the boiler, power flush temporarily solved it but after a couple of months the problem returned. Called a local company who sent an engineer and they claimed the heat exchanger was blocked due to the system being fed through a water softener. Viessman technical told me that was rubbish and that they recommend feeding the system with softened water as the heat exchanger is stainless steel. The company then told me that a replacement heat exchanger was not available. Turned out that the engineer had got the model number garbled and Viessman confirmed that the part was available. The company quoted £2500 to replace the boiler.
Needless to say at that point I threated to report them to trading standards and refused to pay their callout.
I then decided to try to fix it myself, having studied the installation guide I found that it was incorrectly installed. The pump is on the wrong side of the boiler and it was fed with a switched live from the thermostat to the permanent live on the pcb. I rewired it (I am a qualified electrician) and now it is working fine.