Air drawn back into CH system through vent pipe?

[baileyj1976]

This is a bit of a saga, but I will try and be brief. In August 2004 my warm air system packed up, so I forked out for the installation of a fully pumped Honeywell 'S' central heating system. Everything worked great, but there seemed to be a lot of air circulating noisily through the pipework/rads (esp as I have concrete floors downstairs - hence a few exposed inverted loops). After a few weeks of daily air bleeding, the installers came out and reduced the pump speed (!).

This seemed to reduce the problem slightly, but nevertheless when the system started from cold, a lot of gurgling/bubbling from the loft indicated that air was still being drawn in. A few weeks later still and I called them back. This time the chap made some alterations to the vent pipe in the loft, and added a bridging pipe between the cold feed and vent pipes in the airing cupboard (crude air separator?). This appeared to resolve the problem. Plus it was autumn/winter so I didn't feel like taking any more time off work to have the system farted about with (that, and my growing distrust of plumbers!).

So here I am, rapidly approaching another winter. Now the CH is coming on regularly, I am back on the bleeding rounds. There doesn't appear (to my layman's eyes) to be anything wrong with the pipework: the CH vent pipe has more than 18" of head above the expansion tank in the loft, and the pipe exit itself is a couple of inches above the level of water in that tank. There are no leaks from any rads or visible pipework. The only way I can see air getting in is by being sucked back in through the vent pipe (rather than hot water/steam being pushed through).

I have just purchased an official air separator (British Gas approved, apparently) which I am considering getting someone to fit in place of that bridging pipe, but am unsure if that would be a waste of money. Other, less sane ideas include lengthening the vent pipe so that it exits below the water level in the expansion tank - so it would suck water back in rather than air, or fitting some sort of non-return valve to it!

At this stage I am open to any views or advice that users of this forum may wish to share.

Thanks in advance,
James

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[Nige F]

What about your installers` guarantee I`m in Sussex,but it wasn`t me email in profile

 

[baileyj1976]

What about your installers` guarantee I`m in Sussex,but it wasn`t me email in profile

Guarantee on installation was only 6 months. This particular firm have stopped doing basic work in West Sussex, and will only come down from London for new installations (and only agree to do guarantee work on those systems they installed when they are in the same area putting new ones in!).

I do not think they are Cowboys, but the fact that the remedial work involved just chucking in a bridging pipe rather than an actual air separator (one assumes that if a straight piece of pipe would work, people wouldn't sell specifically designed separators in the first place) suggests that they did not try very hard up until the guarantee expired.

 

[PEDANTICVINDICTIVEMAN]

If the pump is 15/60 model instead of a 15/50 then I would recomend a 22mm feed from the tank and use the air seperater as well.

 

[Nige F]

Maybe they are not cowboys but their after sales manager must be called Wyatt....Dahn from the smoke, are they . You get a better service in E. Sussex. We`re just simple country folk. Can you send a pic. of the layout in the airing cupd. pump, valves etc.

 

[baileyj1976]

Mailed some pics to Admin, as I do not have a site that I can upload and link to.

 

[DIYnot]

Here are Bailey's photos:

Picture 1
Picture 2
Picture 3

 

[DP]

Pump orientation is wrong for a start.

Pictures do not help in identifying flow, return, vent and feed pipes.

I have never had to fit an air seperater. Old systems have worked for many years without these. If the plumbing is installed correctly (three tee rule), cannot see a need for these new fangled devices.

DIYnot. Good to see you are back.

 

[baileyj1976]

Pump orientation is wrong for a start.

Er, okay...I actually rotated the pump through 90 deg myself as it seemed to make more sense having the bleed valve at the top rather than on the side (with the speed switch on top)??. In Picture 2, the vent pipe is first to the right of the white plastic overflow pipe, and the feed from the expansion tank is furthest to the right (i.e. the two pipes that have been bridged). I don't even know what the 'three tee rule' is!

 

[meldrew's_mate]

Rotate your pump back so the pump shaft is horizontal, terminal box on top. It won't fix this but it'll make the pump last longer.

From the size of the pipework you should have a boiler no bugger than 18kW (60,000btu/h)

Are you sure it's air being pulled into the system, if it is it will tend to collect in one or two upstairs rads.

It may be corrosion from flux left in the system after the installation, so (and this is a real party piece) get a clear plastic freezer type bag and fill it with "air" from a rad. Tie it to a long pole and hold it away from anything likely to be damaged by fire or explosion. Get one of the local teenage hoodies to set fire to the bag. Does it bang, pop, or burn? If so it's corrosion products, so add flushing agent to the header tank (x300 is good), wait a couple of days, then fully drain & refill the system.

It may also be a good idea to fit your separator now, or at least lower the bridging piece by a couple of feet. This applies even if you can't incinerate said juvenile.

Drain again and refill, adding x100 corrosion inhibitor.
Bleed routine, etc., with diminishing quantities coming out.
Relax and serve tea.


P.S. Don't know if I managed to get a little swear word past the naughty word filter in para 2. If I did, great; if not, it was just a typo Guv.

 

[baileyj1976]

Rotate your pump back so the pump shaft is horizontal, terminal box on top. It won't fix this but it'll make the pump last longer.

Yipe. I'll put it back the way it was then. I have almost exclusively been bleeding large amounts of air from the bathroom rad and one bedroom. Paranoid about corrosion (very soft water round here so minimal scale worries), I spent a weekend in August flushing the system and adding Sentinel inhibitor - as nothing was put in during commission last year. Whilst flushing, nothing came out apart from clear water and bubbles - no rust or other particles.

Over the weekend I spent a few hours balancing the radiators (bought an IR thermometer). System seems quieter in general (pump speed 2), and I have bled almost all the air out for now. Feeling deja vu from last year when I thought the problem was resolved only to come in one cold day to a gurgling bonanza.