had a baxi bermuda gf3 back boiler fitted 18 months ago just replaced two radiators due to decorating thought i would try heating as winter approaches boiler strikes up pump appears to be running ok outlet pipe to pump red hot pipes to emmersion tank red hot and heating tank ok but hot water does not seem to be circulating to radiator valves tried closing valves on radiators except nearest one that allowed that one to heat up but was still cool at bottom opened second nearest which didn't heat up pipes are stone cold i am now completely baffled any ideas?