bleeding radiators daily???

[Fred]

Guys, recently had a combi boiler put in (WB Greenstar 40plus); for whatever reason I have two specific problems:

1) the pressure is increasing over the course of time. I can handle the pressure gauge (bleeding cold system, keeping pressure close to the lower minimum). I realise that the pressure goes up with the heating, but it goes well beyond the recommended upper limit. The emergency valve does not discharge yet, but I also keep bleeding the system regularly.

2) Speaking of bleeding. I bleed the system virtually every night, the attic radiator always has air in it. Should that really be the case? It's a four bed terrace, so the boiler pump has quite a bit of work to do to get the top floor heated, but I did not expect that much air in the radiator.

Any ideas?

Fred

[Set Square]

Are you sure it *is* air? If your system has no inhibitor in it, it could be hydrogen caused by corrosion. Next time you bleed a rad, hold a lighted match in the stream of gas which comes out and see whether it burns with a blue flame.

[andrewpreece]

Make sure your filling loop valves are turned off fully and not allowing mains water to gradually pressurise the system. It doesn't sound like that's your problem, but it would be good to eliminate.

Andy.

[Stuart Noble]

Had a similar situation yesterday in a house where attic rad was cold. Turned the bleed valve with system off, and nothing. No air, no water either. Ran the heating, and still nothing. Turned the filling loop on for

10 secs so that the pressure was up around 2.5, and now quite a bit of hissing, followed by a mug of water, followed by more hissing. Another mug of water and pressure is back to 1.5, except now the water is hot. Obviously not an exact science by any means

[mark b]

Could a floor board nail have been driven into a pipe somewhere. I knew someone who had this problem and it took quite a bit of diagnosing.

mark b

[Aidan]

1) Any automatic air vents, especially at top floor/high level &/or on the return? The system might be under positive pressure when cold, but the pressures throughout the system will change when the pump is running, so it is possible that there is a negative pressure at some points. If there's an open AAV at such a point, it will draw in air with the pump running. If so, close/screw down the cap (like a tyre valve cap)on the AAV . Pressurize the system and only vent the air from the AAV and the problem rad with the system off. See if this solves it.

2) It could be due to hydrogen, as someone's said, but it would be an awful lot of hydrogen. I think the test is to hold an inverted glass over the vent. The H2 rises into the glass & can be lit with a (long) match. If it's this, the system water must be very acidic, probably due to excessive use of active flux (hydrochloric acid). If you could get some litmus paper, you could confirm it. The corrosion will be dissolving your rads. In this case the system needs thorough flushing, neutralising, refilling and dosing with corrosion inhibitor. Did they put an inhibitor in it?