Every time we turn the shower our Worcester 240 combi boiler either ignites and then cuts off 20 seconds later or doesnt ignite at all. heating and hot taps are fine, and I replaced the Mixer in the shower as I had a spare. Also does it when using the Kitchen Mixer tap if you turn on the cold whilst running hot.
Any Ideas

Neil, Plymouth, May 2006

Probably because they are thermostatically controlled and do not draw a constant water pressure through the boiler. The 240 relies on water pressure differential in the diverter valve to activate the water on hot water draw off. Check the shower you have got is a Combi-flow, or is compatable with combi boilers. if not, the diaphragm is up the spout and needs replacing.

craig, plymouth also! well saltash!, May 2006