I switch the gas boiler on which is ok, we had some banging noises from the pipes but after bleeding the system from the rads the banging noises have gone. We still dont have hot rads, after bleeding the rads they get hot for about 30mins then go cold again.
What can I do?

kim yorke, December 2007

I don't think you are getting all of the air out - this situation can often occur after the system has been interfered with - a new radiator fitted for example. I'd try closing the worst radiator off, unscrewing the valves from the rad (NOT from the pipe work!!) and drain the rad. down. Then ,having a decent tray handy open the valves one at a time to let a good quantity of water out. If there is any air trapped, this should clear it. You would then reconnect the radiator and bleed it as normal.

John, December 2007