I have an unvented heating / hot water system and recently replaced the pump as it kept shorting out and blowing the fuse. Since then the pressure gauge on the expansion vessel keeps going up into the red. I release the pressure and within 24 hrs it is back up again and leaking from the overflow / warning pipe. Could this be the filling loop from the mains not closing properly or could you suggest anything else I should investigate? Many Thanks.

Mike, April 2009

disconet the filling loop, if not dripping, most likely the expanshion vessel should be 1.5 bar, turn off the cold water turn on hot tap to take pressur out of cylinder then check vessel using a tyre pressure gage if low use a bike pump to pump up again.

erj, June 2009

Mike, I'd be removing the filling loop if you can (braided steel pipe maybe) to see if water is bypassing the valves. As for the water transfer via heat exchanger, I'd be calling a plumber out who could pressure test the system before diving in. Best of luck with it!

John, April 2009

Many thanks John. Would you be referring to the heat exchanger within the cylinder?? i.e. the coil that contains the heating water? If so then what would be the best approach, replacing the filling loop first to see if it solves the problem, or is there another way of testing.

Mike, April 2009

One of two things, Mike - either the filling loop isn't closing fully or there is water exchange between the two heat exchangers - i.e the DHW exchanger is bleeding into the CH one.
Hope its the filling loop.....!

John, April 2009