I've just fitted a Honeywell programmable thermostat and now my Vaillant combi-boiler won't fire up. No fault message is displaying. Any ideas please?
Help! New thermostat fitted - boiler not firing up!
- Thread starter Ed23
- Start date
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How is it connected to the boiler ?
Is the Domestic Hot Water still working OK?
Is the Domestic Hot Water still working OK?
No the hot water's down too. The thermostat is on the wall in the corridor and should be controlling all the radiators in the house.
Sorry but we need a bit more info to try and find out what's gone wrong.
What wiring changes were made to the boiler when the thermostat was installed?
What wiring changes were made to the boiler when the thermostat was installed?
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None. I just took the old thermostat off the wall and fitted the new one.
The bolier's controlled by a Honeywell timer. The first time I tried to re-start things after fitting the timer I blew a fuse. Everything's now "working" but the boiler won't fire up.
I'm guessing the old thermostat probably used 3 wires whereas lots of newer ones need only 2.
If you were unlucky and got it wrong there's a good chance the thermostat wiring will have shorted the boiler mains and blown a fuse.
If you were unlucky and got it wrong there's a good chance the thermostat wiring will have shorted the boiler mains and blown a fuse.
You're right about the wires. But I do get a display on the boiler - does that mean that its fuse is ok?
When I turn the boiler on, I can hear it try to start up - very briefly - then nothing more happens.
Which model Vaillant boiler is it?
ecoTEC plus
presumably the boiler LCD display is showing a temperature at the moment.
Try pressing the "i" button once, then turn on a hot water tap and make a note of the "S" status codes that come up in the display.
(eg S.10 which indicates "Hot water Demand")
Try pressing the "i" button once, then turn on a hot water tap and make a note of the "S" status codes that come up in the display.
(eg S.10 which indicates "Hot water Demand")
It came up with S.30
That means it doesn't recognise any calls for either hot Water or Central Heating.
It's possible a short circuit has taken out something on the boiler PCB and you'll need some professional help.
I would be inclined to disconnect the room thermostat wiring on the boilers PCB and connect a short wire between terminals 3 & 4 so there is definitely a permanent demand for Central Heating. With any luck the boiler would get the message and at least you wouldn't freeze to death.
EDIT: See page 26 of installation manual http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/ecoTEC_installation_and_servicing.pdf
It's possible a short circuit has taken out something on the boiler PCB and you'll need some professional help.
I would be inclined to disconnect the room thermostat wiring on the boilers PCB and connect a short wire between terminals 3 & 4 so there is definitely a permanent demand for Central Heating. With any luck the boiler would get the message and at least you wouldn't freeze to death.
EDIT: See page 26 of installation manual http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/ecoTEC_installation_and_servicing.pdf
Thanks very much for your help. I'll swallow my pride and go for a professional! Cheers.
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