Hawk II combi - hot water or heating but not both

[bananas and custard]

A friend without internet has a Hawk II combi.

All through the summer he has had hot water OK.

He's just put the heating on and to start with he has heat and water but he hasn't got any hot water when the heating has been on for a couple of hours. If he turns the heating off he can get hot water again.

Any opinions appreciated

 

[kevplumb]

some info might be an idea

 

[bananas and custard]

Only says Hawk II on the boiler.

The manual lists a G20 or G31 variant but the boiler doesn't have an obvious marking although there is a 1995 installation sticker. Installation manual has reference to WRC9207076 on front cover but this may apply to both boilers.

As I posted before:

The hot water has run throughout the summer.
The heating has just been tuned on and to start with there is both heating and hot water output.
Once the heating has been on for around a couple of hours the hot water side stops working unless the heating is turned off.
The heatings works at all times.


If more information is required please ask, I have tried to give all info to hand.

 

[ChrisR]

It's a Ferroli, with a sticky flow switch.

 

[bananas and custard]

An engineer job then!

Would that be a replacement part or can they be freed off?