Hot water down the flow pipe

[Gerard17]

Hi all worcester 240, central heating is fine and the hot water fires up when the tap is open but the water does not get hot. If I leave the heating off and turn the hot tap on the flow pipe gets hot on the central heating. Is it simply the diverter valve?

 

[Alpha man]

Or dhw heat exchanger

 

[R1CKY]

Most likely. Although I know the calorifiers are prone to scaling up on the 240. I know when a plate heat exchanger blocks up it can cause heat to trace in to the heating circuit, no idea if a scaled calorifier has the same effect, but worth bearing in mind.

 

[Billy Bob Bob]

or knackered mixer tap or mixer shower check the basics first

 

[Gerard17]

Thanks for the replies but how could a mixer tap make jt go own the heating pipe?