air getting into heating system?

[chivers]

About a year ago, we had a Worcester Bosch combi installed to replace the old regular boiler, converting our heating from open vented to sealed. This caused one of the rads downstairs to spring a small leak. I replaced the leaky rad a couple of months ago, and replaced the bathroom radiator with a towel rail at the same time.

Problem is: now we keep getting air at the top of the towel rail, which makes a gurgling noise. I've been venting it daily. The air flows for about 2-3 seconds.

I'm woried whether I have a leak somewhere. I've checked all the rads & exposed pipework, but can't see anything. No wet patches in the ceilings. The pressure gauge on the boiler hasn't budged visibly from 1.25 bar since I topped up the system about 6 weeks ago.

Can anyone suggest how to figure out if I have a leak, or how the air is getting in?

Thanks for your suggestions!
- Matt.

PS I read a suggestion about methane build-up from debris in the pipes elsewhere in this forum. I tried holding a lit match to the air/gas as it was vented out, and it definitely isn't flammable.

PPS the missus pointed out that the design of the towel rail would trap loads of air inside the horizontal rungs as it was filled. But since the daily venting has been going on for weeks/months, I would have expected the trapped air to work its way out by now...

 

[cider]

Its probably air being sucked in through poor rad valves on the packing glands.

 

[bgs100engineer]

Air can not be pulled in on a sealed system. the air has been trapped. has the auto air vent been left open on the appliance? this would help free the air in the system. you could try dropping the all the water out through a drain point. then refilling, bleeding each rad till you work your way to the top of the system. or turn off all rads apart from one, let the system run for 30min. then repeat this around the whole system, this should help move any air locks to the top and can be bled out. hope this helps

 

[bengasman]

did you put sufficient inhibitor in the system?
what is the difference on the pressure gauge between a completely cold and full warm system?

 

[powermaxer]

if your towel rail has half inch air vent and blanking off plug at top replace one with an auto air vent.
www.toolstation.com search for 67448 or 34942

 

[landyandy]

PPS the missus pointed out that the design of the towel rail would trap loads of air inside the horizontal rungs as it was filled. But since the daily venting has been going on for weeks/months, I would have expected the trapped air to work its way out by now...

Some of these towel rails can trap a lot of air by their bad design.

Andy.

 

[Bambergaspipe]

Some of these towel rails can trap a lot of air by their bad design.

Not really, the pump is on it`s way out. should be still under warranty though..

 

[swidders]

Problem is: now we keep getting air at the top of the towel rail, which makes a gurgling noise. I've been venting it daily. The air flows for about 2-3 seconds.

The pressure gauge on the boiler hasn't budged visibly from 1.25 bar since I topped up the system about 6 weeks ago.

If you are bleeding daily, the pressure gauge should drop. Tap it with your finger to see if it is jammed

 

[landyandy]

Has the towel rail got flat sectioned horizontal 'rungs', as opposed to the tubular type?

This type can trap air on re-fill.
Have a feel of each 'rung' and if some feel colder than the rest then there is still some air in.

Andy.

 

[Bambergaspipe]

If you are bleeding daily, the pressure gauge should drop. Tap it with your finger to see if it is jammed

After that see if your towel rail is free from air.

 

[Bambergaspipe]

This type can trap air on re-fill.
Have a feel of each 'rung' and if some feel colder than the rest then there is still some air in.

Have a word but I agree it`s air.. produced by a failing pump..

 

[chivers]

Thanks for all the ideas guys. Here's some of the info requested:

Inhibitor: added a whole tube of Fernox Super Concentrate when I filled the system.

Pressure: looking more closely, peaks at about 1.4bar when the boiler's running, drops to about 1.1bar when the boiler thermometer reads 45C. (The missus isn't letting me switch the heating off overnight due to new baby in the house, so right now I can't get a reading with the system completely cold.)

We topped up the system to 1.25bar when it was completely cold about 6 weeks ago. So this suggests we're seeing a modest drop in presure over time after all.

Bambergaspipe, any tips on how to confirm whether the pump's sucking in air?

I was most worried about having a hidden leak. If the consensus of opinion is that I've got persistent trapped air or sucked-in air, I guess I'll fit an auto air vent as powermaxer suggets.

Cheers!
Matt.

 

[Dan Robinson]

Make sure the shaft cover is tight other than that it is unlikely to be the pump.

More likely to be gland on an old rad valve.

 

[Bambergaspipe]

I was most worried about having a hidden leak. If the consensus of opinion is that I've got persistent trapped air or sucked-in air, I guess I'll fit an auto air vent as powermaxer suggets.

Don`t get carred away mate there appears to be nothing wrong wth your heating system, I have a towel rail in my bathroom that gets heated up halfway no matter how I bleed it Down to pipework n sh*it, Chill Dude...

What setting is your pump on.. Turn it to the Max....
then if dat don`t work, replace dat pump...

 

[oilman]

the pump is on it`s way out.

. produced by a failing pump..

Is this man a pump changer? I think we should b told.