The Turbomax 828 allows control of CH and DHW temperature from two knobs on
the front panel. I had set my DHW to about 50C to allow me to wash my hands
in the hot water continuously, but lately I've felt the water is too hot to
keep my hands immersed.

I tried adjusting the front panel DHW temperature control knob, but
it has no effect. The DHW temperature is shown as 66C on the LCD display,
rising to maybe 71C when the boiler has been fired up for 30 seconds. The CH
temperature OTOH is still controllable via its own front panel knob.

Even turning the DHW knob fully ACW has no effect. This problem is
not a show-stopper, as I can live with it, but obviously I'd rather know
what is going on.

OK, it's probably something like a new pcb needed in which case it's
hand-deep-in-pocket time, but I'm wondering whether anyone out there has
experienced this problem, and has found the answer? Also, if I call up the
Vaillant technical helpline, will they have access to technical bulletins
detailing common problems with the Turbomax series, and will they speak to
me ( non-trade )?

As a first level diagnostic test, the potentiometer attached to the
DHW temperature knob appears OK, it behaves electrically in exactly the same
way as the CH potentiometer knob. Also, the temperature sense thermistor
must be working as it picks up the high DHW temperature and sends it to the
LCD display.

There are no fault codes to speak of and the mode and diagnostic
displays offer no obvious clue to any malfunction. Perhaps I'm imagining the
fault!

cheers,

Andy.