OK - just bled the rads as I swore I could hear some air bubbling round and a very mild kettling like sound at the boiler. The highest rad in the system seemed to have a some (a few tablespoons worth really) of what I would term "rusty" water come out (blackish) and then clear, followed by some air, and clear water again.
Does this mean that there was effectively an airlock in that rad?
I had a lot of noise and air - the autobleed valve on the boiler had blocked up. I had a replacement fitted under the service contract - but it would have been a dead easy job costing less than a fiver.
The whole system sounds like it's got air in it (gurgling and whooshing at the 1st rad in the line) but I can't find it (except this pocket that I've just drained) - but the bit that I drained had taken
3 months to build up - and I had to drain a helluva lot of water to get the air to appear. The rad was exhibiting no signs of problems either - no cold spots etc. very odd.
Anyway - I've resigned myself to the fact that once the weather warms
- it's a drain, cleanse, rads off, new locks and therm valves, possibly new rads for two of them anyway (as I mentioned before) - boiler service, and if the boiler is in a good shape still after this winter - a shot of the fernox noise silencer to clean her all down (oh and some inhibitor) over the period of about a month.
AFAIK a decent amount of inhibitor prevents the water from forming air, so if the inhibitor isn't up to strength I imagine the system would be capable of generating air (not sure what variety) in the pipework.
It's there but it's weak - following a partial drain for new rads in an emergency as baby arrived earlier in the year. It's an old sytele open vented system and thanks to BG maintenance had the pump cranked up full and was continuously venting onver :(
Might be worth adding some inhibitor to the header tank - then opening a vent to let some of the water out of the system, thus pulling some inhibitor in from the header tank to increase the mix of inhibitor in the system.
That wouldn't take very long to do, and might solve the problem until you have time (and weather conditions!) on your side.
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