There is a very common fault on a number of Baxi, Potterton and Main combination boilers where a pressure differential switch starts to leak from a spindle that operates a micro switch on hot water demand. Symptoms is a small leak that will usually show as a drip on the left hand side of the boiler casing. It is due to a pressure differential switch design and a part required for repair is sold in a kit called ‘Domestic Hot Water Diaphragm Kit’ Baxi, Potterton or Main number 5111137.
Kit consist of:
This kit will fit following boilers:
Usually there is no need to replace anything else apart for brass nut with metal spacer and small o ring. Over time (some report as quickly as 12 months) internal o ring in brass nut wears off and starts to leak. In majority of cases the diaphragm itself is fine and does not need to be replaced. Removed part shown on picture below (brass nut on the left).
Pressure differential switch with new parts fitted. Water marks clearly visible below pressure differential switch.