I have my hot water set to timed and my heating set to off but when the hot water comes on the heating does too why??

helen, April 2012

im guessing you have a heat only boiler on a Y PLAN
if you are lucky it might just be a faulty timer keeping 3 port divertor valve energised in CH position
if you are unlucky 3PV is probably stuck/seized in MID POSITION [synchro motor knackered]
3PV should normally rest in DHW position [port B] when no demand for CH or DHW
you can test this by switching off CH & DHW on timer & feeling for spring resistance on lever on the side of the 3PV
spring resistance GOOD
no spring resistance BAD
if none of this makes sense to you then you are going to require a heating engineer

manwithnoname, April 2012

Diverter valve faulty

b, April 2012