Alpha CB24 Problem

[Branbling]

Our boiler has developed a new problem.

The heating works ok as does the hot water, but when the hot water has been running for a while the first 2/3 radiators start to warm up.
Can any one tell us what the problem is likely to be ?
Thanks

 

[Agile]

Diverter valve letting by !

Tony

 

[Branbling]

That was quick,
I take it that's the dhw, valve,

Thanks for that.

 

[gas4you]

Just above and to the left of the pump.