Hi, everyone. In the past few days my primary (smaller) feed tank has started to overflow hot water when I run hot water. Investigating in the loft, I found hot water coming in through the vent pipe. Also, running the cold water (e.g. flushing or using kitchen tap) makes cold water flow in at the float valve (even though it\\\'s been replaced and adjusted) to give the same overfilling. Baxi WM552 gas boiler, Wilo Gold 50 c/h pump, \\\"gravity\\\" hot water; system powerflushed 30 months ago. Any help appreciated.