Vaillant TurboMax 824/2 Hot water problem. Diverter valve ?

Hi all
as you'd expect, over Xmas, we had boiler problems. Central heating is fine, radiators getting to top temperature. However, when hot water is switched on, it's only getting to 40C.
I checked the boiler, and it's panel says boiler temperature is running at 75C. But feeling the hot water pipe from the boiler it *really* is 40C.
Initially, switching the heating off, then turning the tap on seemed tp fix it. However now, it's staying at 40, whether then heating is off or not.
Opening the panel, and dropping down the control board exposes the lower gubbins of the boiler. Reading the installation instructions I located the "diverter valve" and gave it a tap with a screwdriver. The output temperature increased to 50C ... but we're back to 40C again.
Do these symptoms point to a diverter valve failure, and what can I expect to pay (1) for the valve and (2) to get it fitted. We have a Homeserve policy on the boiler, but I like to be forearmed, as in my experience they never actually cover anything that can go wrong with the boiler ....
Thanks in advance, and hey .... Happy New Year !!!!
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Bad form to reply to myself, but no one else has ;-)
Having googled further (mainly this group) I'm convinced it's a diverter valve problem... trying to read various posts, it seems that they can be repaired ... is this possible, or desireable, or shall I spash out the 60-80 quid for a new one ?
thanks again
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In message

Indeed. Last Xmas I decided to replace our failing diverter valve (maybe 20 years old) so replaced it with a new one from Horstmann (model F322m). This Xmas, on one of the coldest days of the winter, I found the house getting rapidly cooler. I tested thermostats and then the pump, suspected the boiler, then finally found the diverter valve was stuck on hot water position and making rather pathetic clicking noises when it should have been moving to the radiator circuit position. It contains microswitches through which power from both thermostats flows, so explaining the reason that the boiler logic thought that neither circuit was demanding heat.
I could grouse about a product which failed after 364 days, just when the warranty was about to run out. But this being the season of goodwill, I will instead praise Screwfix who replaced it free of charge right away (though a new one would not have been much over 30 pounds). The other good thing is that the new one was identical to the old, so I only had to replace the motor unit, otherwise I'd have had to drain the whole hot water circuit to replace the valve itself. So our heating system was up and running again the following morning..
It sounds as if your system has a diverter valve right next to or inside the boiler housing so that may be a different kettle of fish. But if it's a well-known brand and only the motor part has failed, then you might also be able to manage by just replacing that bit.
Best of luck,
--
Clive Page

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On Fri, 02 Jan 2009 05:12:10 -0800, Jethro wrote:

I presume this is an early modelo turbomax+ (with a beige control panel and turquiose knobs?). The diverter valve was something of a stock fault on that model. The later models and replacements DVs seem OK.
To confirm that the problem is the diverter valve. You should find that
a) with the heating switched off, the heating flow pipe gets warm when the hot water is run (not just afterwards).
b) you get inconsistent results sometimes things are OK and sometimes not.
c) resetting the boiler can make things better and worse inconsistently.
If you are fairly sure it's the DV then the part is about £100 and fitting would take about an hour all in (or less).
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Hi Ed,
no idea about model, except it was fitted new in 2002. Since the heating is working, it's not a red-alert emergency. And with the family in the house all the time at the moment, I've not had a chance to have the heating off to test (a). However (b) and (c) fit.
Yesterday I removed the little actuator (I guess a motor with position sensor and worm-gears driving the pin). It seems to move correctly (out for HW, in for CH). I have no idea if the pin it connects to is too stiff or not, but figured a little silicone lube wouldn't hurt.
I've googled for prices, 69+VAT is the best I've seen. However I'm cheered by the fact the installatioon manual has a section on how to change it.
Just to check - the job will involve draining the CH and therefore will require a fresh dose of inhibitor when I refill ?
Thanks guys
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On Sun, 04 Jan 2009 09:45:36 -0800, Jethro wrote:

You only need to remove the water (both domestic and primary) from the boiler itself. There are isolators and drain cock to help you. You would be draining <15% of total system volume so no inhibitor needed unless due for a top up.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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