Vaillant 831 hot water

[Scott_D]

Can anyone help with this fault?
Vaillant 831 fitted 2014
Called to look as hot water was poor

Ran some tests and the boiler would only give out 40 degrees DHW
All settings are on Maximum
Diverter not dumping heat down the flow
Boiler modulates down and looses about 20 degrees through the plate heat exchanger at 9 LPM from taps.
Did a factory resret and now it gives 55 degrees.

There are two sensors from what I can see - one on the DHW pipe which is giving a true reading and one on the plate heat exchanger

 

[ShaunCorbs]

What are your getting k wise on the sensors ?

 

[Scott_D]

What are your getting k wise on the sensors ?

I didnt check
I had no data and the tech line was closed last night

I am just looking through the MIs and I cant find any info on the sensor on the plate heat exchanger

 

[Burger]

Could be the display pcb or main pcb. Could try to see if you’re getting the 5vdc on board. Also try the DSN setting in case it’s been changed.

Had a pro 28 the other day, called to replace control knob, turned it back on zero degrees, had to fit a new pcb

 

[Scott_D]

All seemed fine after the reset
Will have to go back with a multi meter if I get called