on this combi when switched to hot water only boiler does not fire at all.on winter /summer boiler fires on hot water but only when heating called. turn on the heating sometimes the boiler fire's but will go to lockout at varying times and some times straight to lock out after 5 to 10 seconds.i have fitted a new thermistor to hot water side and new air pressure switch still have same problem spoke to ravenheat they said requires new pcb. anyone had the same problem thanks

mpg plumb, December 2011

With thw boiler switched off
Take the plastic cover off the microswitch on the side of the diverter valve. Turn on the hot water tap. Look to see if the diverter valve pushes out to press the switch. Mine wasn't coming out far enough to press the switch so never fired the boiler for hot water. I dropped a rubber washer in front of it and it now works. I will clean out the diverter valve at some point as this is the cause. (In my case)

Nick, January 2012