Vaillant ecotec plus 428 question.

jackthom · 4 Nov 2009

This has been working OK for almost 2 years supplying central heating and a hot water storage tank (with extra large heat exchanger coil).

The only slight problem is that the boiler is frequently "caught out" when only required to heat the water tank.
It starts up at reduced power for around 30sec and then takes off at full blast taking the water temperature way over the required temperature and then shutting off for a while. A short while later at the next attempt it has learned it's lesson and keeps going at lower output OK.

The trouble is that once it has had a run with the central heating on, it forgets it has to be more gentle with the DHW and is back to square one.

Is this just a fact of life that has to be put up with or is there some hidden control available on this boiler (apart from d0 which only helps make a compromise) to tell the boiler to take it gently?

picasso · 4 Nov 2009

I dont understand the phrase " only helps make a compromise", if your boiler is over rated for your system (28kw is a big boiler) then down rating it will help your problem, how many kw,s is it set at?

jackthom · 4 Nov 2009

When it's set to something around 14kW there's absolutely no problem. However that would just make the central heating pretty slow at getting up to temperature.

Ideally I'd like to have the whole 28kW for central heating (which has no trouble coping with this output) and something considerably less for the hot water tank on it's own.

I would love there to be a second lower d0 setting which only comes into play when heating the water tank but I suspect there is no such thing.

It's no big deal really

kevindgas · 4 Nov 2009

you would need to fit a VR65 then you can set it up for a lower hot water temperature (AFAIK)

D_Hailsham · 4 Nov 2009

How many kW do your rads add up to? I don't believe it is anything like 28kW, unless you live in Alnwick Castle.

As a guestimate, a 600mm high rad gives off 1kW for each metre length (allow 1.5kw per meter for a double). So just add up the length of all your rads.

jackthom · 4 Nov 2009

D_Hailsham said:
How many kW do your rads add up to? I don't believe it is anything like 28kW, unless you live in Alnwick Castle.

As a guestimate, a 600mm high rad gives off 1kW for each metre length (allow 1.5kw per meter for a double). So just add up the length of all your rads.

You're right, I don't really need the full 28kW at all. I've had the CH running happily (though sluggishly) on around 16kW.

Just the same it would be nice to have the full whack, especially when the heating has just come on from cold plus at the same time the hot water tank is being hammered by my three daughters.

How do the folks in Alnwick Castle cope with the difference in required output between CH and hot water. A combi system I suppose.

jackthom · 4 Nov 2009

kevindgas said:
you would need to fit a VR65 then you can set it up for a lower hot water temperature (AFAIK)

Had a look at the PDF for the V65 but it's difficult to work out what it can actually do. If there was some similar sort of E-Bus control which was capable of tweaking d0, depending on the demands on the boiler, that would do the job.

Having said that the darn thing works reasonably OK at the moment anyway. I'm just being fussy.

kevindgas · 4 Nov 2009

yes it works off Ebus
the 2 temperatures are then set up on the boiler control knobs.
think it works out how hot to go from the demand for heat from the VR65

mickyg · 4 Nov 2009

just leave it set at 14-16kw. Having "the full whack" as you put it is ineficient and wasting gas and is of no benefit whatsoever. The average 3/4bed semi requires around 15kw.

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Vaillant ecotec plus 428 question.

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