hot water discharges from the F&E vent ?

[daveyofgb]

if Hot water discarges from the vent pipe to a F&E cistern when the heating system is running the most likley cause is the the ? this is a question that im trying to find an answer to multiple answers.
1. pump has been installed between the cold feed and vent.
2. F&E cistern has been installed higher than the CWSC.
3. F&E cistern has been installed lower than the CWSC.
4. pump has been installed horrizontal and not vertical.
I would say answer no:4 as this seems to be the most likely but would like to know for sure.

 

[denso13]

2, 3 and 4 are irrelevant. Might be number 1.