Repeated bleeding of sealed system

mwylde · 10 Nov 2003

I have a system new this year with a Worcester Greenstar 27HE system condensing boiler, 3 port valve (external not in boiler) and all new rads and hot water cylinder but using some pre-existing pipework.
I'm having to bleed one rad (furthest away upstairs one) repeatedly. I don't understand how air can get in with primary circuit pressure maintained at 1 Bar or just over (ordinary 2 storey house, not high). Surely the pump can't produce so much "suck" even if there is a leak? And why doesn't any air get out of the automatic vent on the boiler?
There are no leaks apparent and during the summer running on HW only it lost no pressure on the gauge.
Any tips appreciated.
Mike

COG · 10 Nov 2003

Air will naturally rise , so if you have a leak even a very small leak the air will trap and collect at the first chance it gets, in your case a rad so chances are you have a leak on the pipework leading to that rad ,below that rad or at that rad.if your plumber has installed any external auto air vents shut them down that could be the fault they would have only been fitted to help fill the system etc you only need the one on the boiler to run the system. don't use any leak sealer on the system it will block the heat cell on your greenstar big time.

mwylde · 11 Nov 2003

Thanks for your comments COG.
I take your point about the air collecting at the first rad after the leak, but even if there is a leak, how on earth does air get into a pressurised system? It ought to be leaking out not in, but there is no trace of it. Through the summer it held its pressure.
Still puzzled!
Mike

ChrisR · 11 Nov 2003

Corrosion produces gas (hydrogen which you can light!). It's possible that there's some reason for selection of that rad. Do you have a corrosion inhibitor in the system?

COG have you seen leak sealer cause problems for sure? The stuff should only solidify on contact with air. It doesn't seem to block auto air vents though.

COG · 12 Nov 2003

Chris.
iI agree it should block auto air vents but never seen it after countless jobs . Greenstars heat cell becomes very noisy after a few days, not sure of the reason and thats a very expensive part to replace,it may not react with all greenstars but i've only come across two with leak sealer added and they both howled. it may be a reaction with aluminium

mwylde · 12 Nov 2003

Thanks ChrisR.
No I haven't added inhibitor yet - I have some more changes to make to the system (extension) and I was going to use X400 desludger then X100 inhibitor afterwards. However it's all taking longer than expected - doesn't it always! - maybe I'd better put the stuff in.
How long does hydrogen production carry on in a sealed system?Whatever produces it must get used up.
BTW I've got very hard chalky water, not acidic - location East Sussex.
Mike

COG · 16 Nov 2003

X 400 is to remove sludge from an old system, you said you have a new system so should use x300 to remove the flux and such.

mwylde · 16 Nov 2003

Most of the piping is old - it's actually imperial size copper, and unfortunately set in the concrete floor - and I still have 2 old rads (one is 300mm x 3000mm and curved round a bay so I think would cost a fortune to replace) so I thought I should use X400. The old rads I took out were pretty sludgy so I'm guessing pipes will be the same.
Is there really a big difference, I assumed X400 was probably just a bit more aggressive.
Mike

COG · 16 Nov 2003

the sales rep would advise you used both x200 first then x400 BUT if you still have a leak or gas from sludge in a then it would be a sound bet that replacing pie in a concrete floor will solve the problem. you cant properly check pipes in a concrete floor for corrosion .going back to your first text plus the info about old pipes in concrete floor i would advise fitting new pipes at skirting level or sim

mwylde · 19 Nov 2003

Well I tried the flame test, it burns a lovely clean blue so it must be hydrogen from corrosion. Thanks for the tip. I wonder why it only collects in this one rad (which is a brand new one)?
I'd better get the desludger into the system I think.
Substituting for the underfloor pipes is a last resort. Several doorways to cross. In practise I think it would mean putting all the distribution piping in the ceiling with dropping feeds to 6 rads.

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Repeated bleeding of sealed system

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