Over the last few weeks I have noticed that the overflow pipe to the header tank has been dripping, but I have proved that the water is coming into the tank via the outlet pipe (I've emptied the tank and dried it, then watched the water slowly fill the tank from the bottom outlet pipe) The tank outlet pipe feeds to the pump - a Grundfos Selectric UPS 15/50.Is there anything I can do to rectify this problem or do I need a new pump? Although the heating system is currently off I did put it 'on' & bleed all the radiators and I have checked that the pump rotates freely. The system seems to work very well other than the problem described.

Ian Fyfe, July 2012

if the tank is filling up from the bottom of the tank then the boiler is fine, it would be the hot water cylinder coil internally split and water is over filling the cylinder and escaping to the tank. If the water is coming into the tank from a pipe that hangs over the top of it then you possibly have a blocked pipe section

andy, July 2012

Hi Toptrish & Ltd - Not a combi boiler, it's a Potterton 'Profile' 50e and the systems been installed for 19 years & is as described by 'ltd'. As you have both suggested that the Heat Exchanger is faulty I will try the power flush solution. As I'm neither a plumber nor central heating engineer the simpler the solution the better. (I assume I just have to pour the solution into the header tank and run the system as suggested). Will advise on results. Thank you for your responses.

Ian Fyfe, July 2012

Look like you have old boiler with hot water cylinder an expansion tank ,boiler heat exchanger is block you need power flush or DIY put slug remover 2lit run system for two week and flush out and put MB1

ltd, July 2012

Is it a combi boiler, if so it could be water from the cold mains leaking into the heating system the best way to tell is to do what you have done before by emptying the tank, underneath the boiler there should be an isolator for the cold mains input to the boiler turn this off and see if it stops the problem if it does it sounds like it could be the heat exchanger that is faulty

toptrish, July 2012