Viessmann experts, advice please

[Sid Viscous]

Evening all, having a few issues with a Vitodens 100 WB1B combi.
About 9 months I had to change the p2p hx & dhw flow switch. All fine until this morning when custard called to say he had no c/h, hot water fine but boiler running constantly with water icon on screen. Had a look just now & discovered if I turn dhw temp control to 0 the c/h comes on. Turn the temp control up to only 1 & c/h goes off & water icon comes on screen. Any advice on what to check welcome please.

 

[ShaunCorbs]

How old is the boiler ?

 

[townfanjon]

Any damp / water on the board , try a hair dryer on it

 

[Sid Viscous]

Pretty old one I think.
No sign of internal leaks or dampness.

I have several of these on my books, this is the only one I've ever had to repair so I'm a little surprised it's gone again. P.S. Viessmann people - Parts stupidly expensive!!