Vaillant combi constantly on

Fitch_2

Hi there. First post, probably not in the right forum -please forgive.

Anyway, had my old Vaillant VCW GB 221 H serviced 6 months ago and apparently it needed a new motherboard (£119).
6 months later, just as its getting cold, I switch on the central heating, which kicks in full pelt 24 hours a day, this is with temperature knob set to 1 (the lowest setting), the switch set to water only and the timer in the "off" position.

Same bloke who replaced the motherboard 6 months previously (from Vaillant themselves) says it's the motherboard again, and that as they only have a 3 month guarantee, I have to buy another one.

If it is the motherboard, what part? any circuit diagrams out there? the most expensive component looks to be a planar transistor (app. £1.40), so if this is a known problem with a cheaper fix (30 years electronics experience), then I'm all for it...

Yours in eager anticipation.....

Canucklehead

Hi

Did you find this 'bloke' from a well known phone book?? because it sounds like the kind of thing some 'engineers' do to keep coming back time after time.(or was he really from Vaillant?)
Was there a reason you had him in to service the boiler? was there a problem?
You wouldn't need a new PCB in a service, only if it had packed up.

You need to establish that external controls are not giving the boiler a call for heat.Next would be the internal wiring which could have been screwed up from the first visit.
This doesn't come across as a very competent job.

Corgi Guy.

Fitch_2

Yup, definitely from Vaillant. Vaillant van, Vaillant paperwork, Vaillant phone number.

The first call out was because I'd just started a yearly service contract with Vaillant.
The second call out was because of the fault described.
I said no to a new board.

Where would I get the installation guide for this baby, with that, I can then check the wiring, and beetle off to B&Q to get a new thermostat/timer with some confidence that I'll be able to fit it correctly, see if what you suggest is right.

ni4abargain

We had the same problem with our Vaillant boiler just a few weeks ago - how weird. OH reset the boiler and it's been okay since - touch wood.

Canucklehead

Hi

I ordered an installation manual from Vaillant via their website, got a reply confirming order,that was 2 weeks ago!

Sometimes there are wiring diagrams tucked away inside the PCB compartment or a stick on one on the back of the door panel /top casing.

Can't seem to find any thing online .

It might be worth a post on www.diynot.com

Corgi Guy.

Snow_Dog

First thing I would check is the sensors feeding the information into the PCB.

As Canucklehead said you may find a basic wiring diagram giving the I/O connections inside somewhere, failing that trace the wiring. Is it possible the thermostat is duff, demanding permanent CH, does the boiler have an independant frost stat, is so it could be that that is demanding heat to the CH.

In the few boilers i've had dealings with i've not had a PCB failure yet, usually sensors, eg fan sensor, DHW temp sensor etc. These are usually a tad cheaper than PCBs.

Fitch_2

Fixed! - so far..

Thanks all.

I replaced the timer whose wiring was wierd. Also, I think the thermocouple or whatever it is inside the boiler is duff as a setting of 1 is the same as a setting of 9 i.e. hot. (bit like me)

However I replaced the timer with a new fangled programmable room thermostat for 40 squid and it works a dream. OK, I connected it up 123 - 345 and realised after very little time to connect it the other way round (321 - 345, but after that little glitch it works perfectly.

On the next "service" I'll get the bloke to check the internal thermocouple.

Thanks for all your help, it put me in the right direction.

P.S. Canucklehead, do you want a copy of the manual?, which I eventually found.

Canucklehead

Hi

Thanks I'll bear it in mind if I need it! You might be able to follow the manual through and work out what bit needs replacing on the internal boiler stat it might be that that is where the new PCB fits into the plan or a sensor on internal pipework.
Glad you got it fixed.
Corgi Guy.

kanes_son

Sorry to bump this, but I am having a problem with the same boiler.

The pilot light went out a couple of weeks ago, but when the landlord came round, he fixed it immediately and it worked.

Now the bloody thing has gone out again, and I've tried the exact same thing again, but of course, it won't work for me.

Can anyone help, it's cold and that's not going to help my fibro, and my landlord is at work