"Ed Sirett" wrote in message
news
On Sat, 18 Sep 2004 02:43:24 +0100, andrewpreece wrote:

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!

Well you have gone through all the things I would have done to check it
out. There is only one more test I can think of which is does the "Hot
Standby mode" on/off function work. I.e. If you turn the DHW knob fuly
clock
wise the green light comes on if you turn it full anti-clock it goes off?
There are slight detents at the top and bottom of the range but I don't
think these correspond to extra switches just the hi/lo end of the "pot".

I suppose there might be a poor connection between the pot. in the PCB?
Anyway it all looks like a new PCB.

See if geoff at cetltd.com does them, he lists a Turbomax board but I
don't
know whether this is for a Turbomax or Turbomax+ (your one). The price is
around half the £150 that Vaillant would want. The part number he quotes
is not the one I have listed for the Turbomax+.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html



Hello Ed,

Thanks for replying and for the info. The situation is more
complicated than I thought, and I'm beginning to question my memory now! I
tried again today to investigate, and found that fully ACW the hot water
knob will get me water at 65C, whereas at fully CW, the temperature reaches
76C (after 30 secs ). This means the combi is responding to demand, but I'm
perplexed as I swear I remember being able to dial up 50C last year. A range
of about 10C for DHW temperature control doesn't seem very large.

I also got the Vaillant into diagnostic mode and dialled up the
modulator current, which I presume corresponds to gas modulation. I found
that turning the DHW knob ACW, when demanding HW from a tap, caused the
modulator current to drop like a stone, though it springs back a bit, so
this confirms the DHW knob really is having an effect.

I shall just leave the DHW knob fully ACW for the time being and live
with water at 65C, as that's an improvement on the recent situation (70C).
I am wondering if the groundwater temperature effects things? I thought the
Vaillant delivered water at absolute temperatures, not relative. I last
adjusted it in december, when things were cooler. Also, I wonder if I am
confusing memories about the CH temp control, which shows demand ( as
opposed to actual ) with DHW in my memory.....

Finally, I tested the combi this time with a small cloakroom basin
hot water tap which didn't exist when the combi went in, and I wonder if a
higher flow rate would give different results? ( shouldn't matter though as
I rarely turn a hot water tap on full except for the bath ).

thanks anyway,

Andy.