Powerflushing is a generic term for using a high flow-rate pump and chemical combination to restore circulation to a restricted central heating system. A microbore system with twin entry valves can be powerflushed, but not very effectively. My company carries out powerflushing, but we would advise that you DO NOT use an acidic powerflushing chemical with microbore systems, irrespective of whether it has twin entry or single entry valves (there are non acidic versions on the market that would be suitable). This is because you cannot get an adequate flow-rate through the pipework to neutralise the acid afterwards. During the process of powerflushing, carbon dioxide is given off, and if not completely neutralised, will result in continuall gassing of the radiators. Before you go to the extent of powerflushing, I would advise that you try a non acidic restoring chemical such as Sentinal X400 that can be added via the header tank, and left in the system for up to 1 week before flushing out simply by draining the system in the normal way (the draining and refilling will need to be done 3 - 4 times to get all of the X400 out of the system). If this does not resolve the problem, then consider powerflushing, but get some additional quotes as your cos seems a bit on the high side. Also get your plumber to seperate the cost of the powerflush from the valve replacement (which should now be thermostatic radiators valves that he is installing to comply with Part L of the Building Regulations). Our average charge for powerflushing is around £420.00 + vat, but bear in mind that different areas of the country vary. Dave Hickey
