you need to give more info does the burner fire up if it does then check central heating pipes if their getting warmer if they are then you need new diverter valve diaphragm. If their not then check you secondary heat exchanger that might be sledged up just take it off and run it under tap. last check the flow switch just above the diverter valve if the spindle is not coming up change the diaphragm
hope that helps
goplumbing.co.uk
jan goplumbing.co.uk, August 2012
