I HAVE A POTTERTON COMBI GAS BOILER THE 15mm PIPE THAT GOES OUTSIDE KEEPS LEAKING WATER AFTER CENTRAL HEATING SWITCH ON .THE PRESSURE DROPS WHEN C/H SWITCH ON AFTER AWHILE I HAVE TO REPRESSURE TO GET H/W THIS IS O/K BUT AS SOON AS C/H SWITCH ON WATER APPEARS TO LEAK OUT OF PIPE OUTSIDE IT ONLY HAPPENS WHEN C/H ON.

MR J SPENCE, September 2007

u need to recharge the expansion vessle to 1 bar with the no back pressure on the boiler

kris, September 2007