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

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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

Cap up the 15mm pipe at the tank and put an air vent on it. Divert the 22mm
open vent to the bottom and convert it to a combined vent and feed system.
That will stop the splash over. It is not pumping over.

Depending on room of course an air ejector may be used in a one pipe
system - Ideal recommend one of these in combined feed and expansion F&E
tanks.