A neighbour has a Gledhill thermal store, a square one, fitted on the first floor and the boiler on the ground floor. The F&E tank is at high level in the cupboard the thermal store is inabout 3 feet above the thermal store. This is a hot water only thermal store and the CH system is normal using a pump for CH and DHW and no zone valves. This is a flow pipe, a tee and two pumps, one for CH and one for DHW. Both pumps are in the casing. On the flow pipe from the boiler the open vent pipe is taken off near the thermal store in 22mm and just loops over the F&E tank with no right up and over (there is no room) with the cold feed from the F&E tank in 15mm teed into the flow pipe directly after the open vent tee. This means that both pipes have the same pull on them from the pump, which is after the tees. All is fine untill a pump stops running and then a dribble of water enters the F&E tank. Will this affect the system in any way? How can it be prevented? Any valves or the likes to stop this? It can be easily converted to a one pipe combined feed and expansion system, this this OK?
TIA