I have just had a bathroom professionally renovated. As part of this work a new boiler, CH pump and F&E tank ball valve were also installed. My boiler and central heating is an open vent system and was powerflushed as part of the boiler replacement.
A couple of weeks after the installation I noticed that hot water was surging via the CH expansion pipe into the F&E tank, yet the CH is switched off. I will be contacting the plumber who installed the boiler to look at the problem but would also very much appreciate the advice of this forum.