"Ed Sirett" wrote in message
news
On Sat, 18 Sep 2004 16:38:29 +0100, andrewpreece wrote:
"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,
AFIK the display shows the temperature of the primary water as it exits
the DHW exchanger ('sardine can'). This is the only NTC sensor in the box.
Since a little water always flows through the primary side [1] of the
'can'
this shows the primary flow temp in CH mode and approx HW delivery temp
in HW mode.
Even if the flow rate is very poor the HW temp should not exceed the
maximum specified by the DHW temp knob, if necessary the gas will be cut.
The range should be something like 45-75C.
Perhaps there are some fixed or preset resistors on the pcb near the pot.
pot which have gone awry.
Does the Hot-Standby-Selection feature work?
[1] That's how the bypass circuit is implemented.
--
Just a correction to my last post, the warmstart works ok, but although the
diagnostics said it was at 48C, in fact it is variable via the DHW knob from
30-60C ( diagnostic display varies instantaneously with the HW knob
position, so that's obviously a demand figure ), showing the DHW pot works
OK and that info at least is getting to the display. The book says the
warmstart temp can be varied between 40C and 65C however, so I'm not sure
it's still in kilter. I must say that the diagnostics function is a great
help on this boiler, it may not tell everything but I'd be messing around
with voltmeters and thermometers without it.
Andy.