Air from micro leak or kettling?

[kev999]

Hi everyone,

I replaced my rusty radiators and re-did most of the plumbing last autumn - with 22mm & 15mm copper. It works very well now; no water leaks, good flow rates etc. But there seems to be air/gas getting into it, or at least I've been bleeding small amounts out of a radiator for months but its not got rid of it yet, and its quite noisy at times when the little bubbles collect together into big ones.

Does anyone know if a kettling boiler can cause this? Its old and scaled up so kettles even with high flow rates, but its still working so i was waiting until warmer weather to deal with it.

I don't 'think' it could be gas from corrosion. I couldn't seem to light what came out of the bleed valve, and most of the rads and pipework is new. I also cleaned it all with fernox F3 once it was finished, then flushed and filled with MB-1 (which still seems to be working when I tested it with a steel nail).

The only other thing i've come across is the possibility of a 'micro leak' which doesn't let water out but lets air in. I've put external sealer around the pump conectors and a few other places and have tightened all the compression fittings that i can still get to but that hasn't helped. There are loads of valves with compression fittings (rad valves, TRVs, zone valves, isolating valves and a bypass valve) but I used solder-ring on the pipework itself, which I've usually found to be reliable.

Any advice on finding the cause would be really appreciated; I'm under pressure to start putting plasterboard and floors/carpets back but am a bit nervous of covering things up until this is sorted!

Thanks,
Kev

 

[sonray ltd]

need info on type of system.

 

[kev999]

need info on type of system.

oops - forgot, sorry. Its a traditional open/vented system, with an old glow-worm boiler, one pump, two zone valves (upstairs and downstairs) plus one for the HW (cylinder thermostat), and an automatic bypass valve between a point just after the output from the pump and the last junction before the boiler on the return. Most rads have TRVs on them.

Cheers
kevin

 

[sonray ltd]

have you checked its not drawing air down the vent pipe when system running ?

 

[kev999]

have you checked its not drawing air down the vent pipe when system running ?

Good point - yes i checked this and it seemed to be okay when I was looking at it, maybe I should check with different valves shut/open and so on.

The 15mm feed is just before the pump and the 22mm vent pipe is about 5" back from that so the configuration seems right. But the pump is up near the ceiling and the tank water level is only about 18" above it, so there's not a great deal of head.

Thanks for the suggestion!

Cheers
kevin

 

[stevetheplumber]

good point - yes i checked this and it seemed to be okay when i was looking at it, maybe i should check with different valves shut/open and so on.

The 15mm feed is just before the pump and the 22mm vent pipe is about 5" back from that so the configuration seems right. But the pump is up near the ceiling and the tank water level is only about 18" above it, so there's not a great deal of head.

Thanks for the suggestion!

Cheers
kevin

almost certain to be sucking in air if the vent cold feed is that shortprobably needs a air seperator or oversixed vent pipe

 

[kev999]

Thanks!

You could both be spot on. I did a few more tests last night, its a bit difficult to tell for sure because its over quite quickly, but I think in some cases (different zones on) it may be drawing in air slightly when the pump starts up.

Sadly, there's not room for an air seperator without a fairly major alteration to the pipe work. It could be done if necessary, though. I may also be able to raise the feed/expansion tank six or seven inches if thats likely to help much?

Alternatively, perhaps I could cap the 15mm feed pipe and turn the current 22mm vent pipe into a combined feed/vent. The boiler (Glow-Worm Fuelsaver 50B mkII) does have an over-heat sensor but its manual doesn't mention a combined feed/vent pipe as an option so I'm not sure about doing so. It would be easy to do this, but do you think this sounds like a good idea or a bad one?

Thanks again, would have taken me months to track this one down!

Kev