The domestic hot water is not working at a constant temp or may not work at all, wheather the heating is on or off. The heating works ok but when the call for domestic water is needed the burners switch on and off at 20 second-ish intervals. this is the same when no heating is calling. New diaphragm fitted, pressure vessel at 1 bar, can throw water out of vent, pressure increases when system running.

Graeme, January 2006

Has the flow of the hot water dropped or increased any since this started? if it has dropped in flow then it sounds like you have a blockage in the pipework redustricting the flow and causing the wter to heat up within the boiler and then start to cycle the boiler, if the flow has not altered you will probaly need to descale the heat exchager or replace it.

Lee, January 2006