dhw problem

[mattydrake7]

i have a problem with my DHW the heating is fine and the heat exchanger has been descaled recently the water runs hot for around 15 seconds then goes cold the pressure is fine i was wondering if it is a electrical fault ?

its a worcester 24cdi rsf l combi

 

[petit_pablo]

Does the tap light come on when you run a hw tap?

 

[twgas]

It might be electrical, but, how was the h/ex cleaned (and which one)

 

[mattydrake7]

yh the light comes on for a few seconds then goes straight off

 

[mattydrake7]

i dnt no hw it was cleaned it is my nans boiler she told me she had it clean around 2 months ago it was the main heat exchanger at the front thanks

 

[twgas]

yh the light comes on for a few seconds then goes straight off

this sounds like the diaphragm in the diverter valve.

the main heat exchanger at the front thanks

the main h/ex is not at the front, so I'll assume it was the water to water h/ex.
After re-reading your first post I don't think it's the h/ex, a partial blockage in there would cause hot-cold-hot-cold, I believe you're saying it warms up then goes, and stays, cold