Hot water from Combi intermitant

[tvrjohn]

Hi Worcester 28CDI Combi, all works ok except that it won't deliver hot water constantly, flames stop and restarts after few seconds.

What is the diagnosis please

 

[gigz]

Blocked plate possibly. Is there plenty of flow at the tap ?

 

[tvrjohn]

gigz, Yes plenty of flow, just stops heating then cuts back in again