Resurrecting an old thread but have to say; taxes replies are spot on. Thanks for your clear advice.
I don't know if suts89 tried to dismantle & clean the flow gauges? I am flushing my system at the mo' & was wondering if they came apart.
Regarding this particular Nu-heat system, which appears to be the same type as ours, there are no automatic air bleed valves on the manifold. There is a std radiator manual bleed valve on the flow bar. Some other makes no doubt have auto bleeds on them. I read the latest Nu-heat (brass) manifolds have isolator valves to enable the gauges to be removed for cleaning without de-pressuring.
Our system - 3 years old - has been great, no probs, but has the same deposits on the glass of the flow gauges making them unreadable. I am certain it is rust. Our CH system includes radiators (some 1930's cast iron ones also) so there is a lot more potential for rust / sludge than in a UFH only system. It had
screwfix inhibitor in it. I would be very surprised to see so much deposit in a plastic/ally/brass UFH only system.
I have just installed a Fernox Tf1 filter & there was a lot of c**p in it when I first cleaned it! This suggests insufficient qty of inhibitor in system. I cannot stress enough the need for a filter in your CH. particularly in a UFH / steel rad mix like ours. UFH suppliers should make a point of recommending it in mixed systems. Before our UFH, the previous boiler (BG installed) packed up at 5 years! - due to the amount of c**p. The entire ancient pipework was steel. All gone now. A £100 filter would have saved a lot of expense...
I also read elsewhere that people had problems with split & bursting UFH pipes - in slabs! - some of it will be bad install's, some poor or now obsolete materials - . Plastic pipe systems are vulnerable to excessive heat. UFH systems are not designed for radiator temperature water through them. You should have a cold feed & use a mixer valve on the flow to manifold if you have rads. Failing that, turn your boiler down! I read that condensers work better at lower temps.