Central heating Expansion tank is getting back flow of water from hot water tank

[ozi]

When the roomstat activates the pump water is forced into the CH expansion tank via the 1/2 inch feeder pipe forcing the level in expansion tanl to rise up to the level of overflow pipe in exp tank causing a slow trickle from the oveflow pipe. When the pump cuts out the flow stops after a few seconds however the level in the exp tank does not drop. Alos it is hot water which is drawn up the pipe into the exp tank. Any ideas why this may be? I have been told it may be sludge in the bottom of hot water tank after all it is 20+ years old.

 

[GasmanxxxR1]

If the cold feed is teed into the return try capping it off there and tee it directly into the open vent, obviously bellow the water level of the tank

 

[BLOD]

Sounds like it Could be a split coil in the cylinder.

 

[Gray0689]

Sounds like it Could be a split coil in the cylinder.

No then it would overflow all the time depending on heights of tanks

Is there a vent pipe?

 

[BLOD]

No then it would overflow all the time depending on heights of tanks

Gray - you're probably right, although I did have one a while back where the coil fracture (multi microbore) only allowed water to pass through when the pump was running.

ozi - perhaps you can post a picture of the pipework where the cod feed/vent joins onto the system ?