Radiators hot while running hot water taps

[mickr]

System is:vcw-sine 18 t3 w (gc- no. 47 044 01)
While running the hot water tap the radiators get hot without the heating being on.
I have looked through the forum but still confused as to what part fault could cause this.
I have an instruction book and thinking if this is a diy job (i know its an old boiler,but seemed to be reliable).
Any advice and tips to repair fault would be much appreciated.
Thanks in advance

 

[GasAid]

Diverter valve

 

[uug197h]

i agree with gasaid
or plumbed in wrong

 

[mickr]

Thanks for the reply but when you say diverter valve is this the flow switch in the manual.Do i replace the valve or does it contain parts that can be replaced,i.e diagpham,wax capsule(thermostatic element)?
thanks mick

 

[ChrisR]

Wax cap is a common one to go , and replaceable.

 

[mickr]

Fitted new wax capsule two days ago and boiler seems to be back to form.
thanks for your advice much appreciatted