Header tank filling through cold feed.

[joe plumber]

Need some help with this one. Have an old 3 pipe system in a pub Which fills the header tank via its cold fill and subsiquently overflows. The cylinder is 2 years old as it was replaced due to to splitting its also had the cf and ov moved to correct location behind pump. It's also had a pump and 2 port added to the cylinder flow. I think this may be where the problem lies. When the ch is off zone valves closed but cylinder calling for heat it keeps the pump on the heating circuit running meaning its pumping nowhere and then forcing its way up the cold feed ?????

Any help would be greatly appreciated or if you think I've missed something.

 

[leethegasman]

if you have two ports on the system and they are closed and you have a pump over run then there should be a bypass on system preferably auto bypass