Baxi Instant 80HE issues

[Sid Viscous]

Hi All, got an issue with an Instant 80HE. I've done a couple of jobs on it already - replaced expansion/storage vessel & the 3 way solenoid head. Been back to it again today. When the preheat is used it all works fine until it reaches temperature. Then the dhw light stops flashing & stays on and the fan runs constantly. The custard says it does the same in c/h mode also, although I haven't seen this myself. Any ideas welcome please

 

[lame plumber]

check the dhw flow switch ok or pcb is on its wayout, have a look at the manual http://www.baxi.co.uk/docs/Baxi_Combi_Instant_HE_Installation_and_Servicing_Instructions.pdf

 

[Sid Viscous]

Checked MI's - useless! Also proved APS as I know these can be dodgy on this model.

 

[lame plumber]

my easy check is to swap pcb for 2nd hand one in van

 

[Sid Viscous]

Don't have that luxury dude, ain't scrapped one of these yet

 

[bewsh]

Have you checked if there's continuity through the dhw micro switch?

If you turn the pre-heat off, does the dhw led stay illuminated?

 

[Leo21]

Have you checked if there's continuity through the dhw micro switch?

If you turn the pre-heat off, does the dhw led stay illuminated?

Sounds like the dhw switch is stuck on, closed circuit.

 

[arran197]

Ye I'd go with that too.

 

[neily01]

Had one of these before pop the flow switch off and see if the light goes out

 

[Leo21]

Actually that's a good point, micro switch stuck or pin in differential valve seized.

 

[neily01]

Think it was a stuck pin last time so the boiler thought their was a hw demand and because of the preheat it just ran all of the time. Was intermittent to start with and I was called there because of intermittent htg