I have a detached house with a fully pumped open vent HWS & heating system. Pump is twin head, with head 1 serving HWS and head 2 serving rads. We have lived here for 6 years with no real problem, however, over the last month I have had problems with the entire 1st floor rads draining of water and filling with air ! When this happens, the F&E tank is overflowing, pouring out of the overflow and the make-up pipe from the F&E tank is pretty hot, but water in F&E tank seems cool ?? Unlike most installations, the expansion pipe and F&E make-up pipe do NOT connect into the system prior to the pump, but extend from the HWS calorifier heating Flow and return pipework. boiler flow to calorifier branches to the calorifier and then continues up to connect to make-up boss on F&E tank and the boiler return from the calorifer branches to the ground floor boiler with a branch that extends up to the loft as the expansion pipe. If the plumbing arrangement is wrong,.... why has it worked for last 6 years... ditto pump speed if over pumping is the cause. boiler and pump are at ground floor level. Can anyone shed any light on what maybe happening ?? Thanks 
