back again some of you my have read last problem with pump (ch at wits end)replaced pump (new) had another bash today vented drained system seemed ok boiler starts now have warm not hot rads up and down(suspected air lock)but for some reason boiler cutting out just after it lights trying to light (clicking)looked at old fault manual for boiler (flow chart) says something of bypass valve in between flow and return this is closed is this right anyway thanks for your help in the past and future and would have got back to you ages ago but only had time to have another look today got to get it sorted before winter.