Hot water/heating problems with Vaillant EcoTec Plus 824

16 Apr 2008
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United Kingdom
Hi there,

I've just moved into a flat with a new boiler as above, and have had a lot of niggles with the system, still ongoing. Despite the maintenance company's protestations that it's working fine, I'm sure it isn't.

Here's my list of symptoms:

If the heating is on and running (ie the thermostat (central thermostat) is set high) heating is nice and hot and the water runs lovely and hot quickly, regardless as to whether the HW Warmstart function is on or off.

If the heating is off (or the thermostat is turned right down) and Warmstart is OFF, the water never gets more than lukewarm, in fact it alternates between lukewarm and cold. I've tried running the taps for more than 10 minutes and it never gets hot, even though there's loads of exhaust and steam pumping out of the flue.

If the heating is OFF as above, and the Warmstart is ON, we get hot water, but despite the CH being off the radiators get hot as if we'd never turned it off at the thermostat. This is going to be a nightmare in Summer - to have HW available the house is going to be baking!

I am looking for someone to tell me if this is expected behaviour or if not, what the problem probably is so I can go back to my Landlord with an expert opinion.

To me it feels like a diverter valve problem, ie it's operating incorrectly in some settings or not at all (eg in the CH off/Warmstart off mode).

Any help offered very gratefully accepted.
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I'd say you're about right!
If you have the warmsrtart OFF, does the CH flow pipe get hot when you turn the HW on?

You probably also have a partially blocked HW heat exchanger.
All that for a brand new boiler!

When the boiler cools down I will check the CH flow pipe with the hot tap on.


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Yes, when I ran the tap with with WS off and the hot water was flowing down the CH pipes.

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