Worcester

[Hobo128]

Worcester 28 I rsf I think.
No hot water . Open hot tap and pressure diff makes contact with micro switch, boiler fires but no hot water, central heating get warm. ???? I'm thinking pressure diff is blocked

 

[GrahamM]

If defo the 28i RSF with no plate hex and is ok on heating itself sounds liked blocked heat exchanger.

 

[Aquazone]

I think if there's a microswitch and diaphragm then it must be CDI I would think. Probably diverter passing to heating if so.