Two possible causes, both easy to fix if you are mechanically adept. Download and read the manual from Vokera web site first.
1)Most common. Your Domestic hot water diaphragm has a hole in it. Disconnect boiler from electricity supply. Remove outer casing. Remove grill underneath boiler for access (two self tappers at front corners). Remove fulcrum arm (slotted screw). Turn of the cold water supply. Remove five posidrive/bolt screws (may need spanner on flats to shift them) on DHW diaphragm cover. Remove old diaphragm and carefully and thoroughly remove all traces of stuck on diaphragm from the metal and from plastic pusher plate. Fit new diaphragm and reassemble. If you get drips from where the fulcrum arm actuator pin goes through you need a new o ring holder assembly. This (and the diaphragm) is part of the service kit t0019.
2)Far less common: Your domestic hot water demand microswitch is broken. Easy job to replace. When moved it should have a nice positive 'clicky' action; a dead flesh type movement means it is broken. The boiler flow microswitch also sometimes fails, either causing pilot flame outages and potentially unsafe boiler operation, or a complete refusal to fire up the burners. These microswitches seem to go intermittent before failing completely and can be difficult to diagnose.
c, November 2007
