Potterton Boiler not firing up

I need some advice on a Potterton Boiler.
It's an old ground standing unit and has worked fine since its installation 26 years ago but is now not firing up. The power supply to the control unit seems ok and there are no loose wires, the pilot light is ok and I've had a look for a fuse but can't see one. I'm therefore guessing it can only be one of two components within the boiler itself.
The first is the thermostat but this looks ok to me. It's only a simple device and again there are no loose wires.
The second is the main unit (not sure of it's proper name) that controls the gas flow. This is a sealed unit that again looks ok to me with no obvious problems.
I'm not an expert on boilers but am a reasonably competent DIYer but I don't know where to go from here. Any advice would be much appreciated.
Thanks.
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On 14 Jun 2005 02:03:22 -0700, snipped-for-privacy@yahoo.com wrote:

What is the model of this boiler? I have a 33 year old Potterton floor standing boiler and I *may* have a wiring diagram for it..
I'd see that the timer is set correctly. Next I'd check the boiler thermostat, cylinder stat (If fitted) then the Honeywell valve. Obviously the problem could also be the wiring going to any of these devices.
Even if the Honeywell valve is faulty, these can be bought cheaply on ebay.
sponix
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That's even older than my Kingfisher. It's not quite 30 years old but still going strong.
Any advance on 33 years?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Tue, 14 Jun 2005 11:44:12 +0100, "Dave Plowman (News)"

Still got the original installation instructions for it, complete with pencilled notes made by the plumber!
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The card I have gives the model as a "Potterton Kingfisher CF45 & 55".
The timer is correctly set and there is no obvious fault but I'm no expert.
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On 14 Jun 2005 09:04:42 -0700, snipped-for-privacy@yahoo.com wrote:

The documents I have cover the C40/12 (Which I have), C50/12, C70/21, C80/23 and C95/28 models.
sponix
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On 14 Jun 2005 09:04:42 -0700, snipped-for-privacy@yahoo.com wrote:

Try looking at http://www.partsarena.com/baxi
This has installation instructions, user instructions and parts diagrams for your boiler.
Ian
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On 14 Jun 2005 09:04:42 -0700, snipped-for-privacy@yahoo.com wrote:

Try looking at http://www.partsarena.com/baxi
This has installation instructions, user instructions and parts diagrams for your boiler.
Ian
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On 14 Jun 2005 09:04:42 -0700, snipped-for-privacy@yahoo.com wrote:

Try looking at http://www.partsarena.com/baxi
This has installation instructions, user instructions and parts diagrams for your boiler.
Ian
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Most likely the thermocouple. That's the device which pokes into the pilot light and has a thin copper tube going to the gas valve. It senses the pilot light being alive and well and then allows the gas valve to open on demand. If it's faulty, the gas valve won't open.
You'll get one from some B&Q etc, or any PM for a few quid.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Tue, 14 Jun 2005 11:02:47 +0100, "Dave Plowman (News)"

I'm pretty sure that on these boilers, if the thermocouple fails then the pilot light will also go out.
sponix
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On Tue, 14 Jun 2005 11:02:47 +0100, Dave Plowman (News) wrote:

True but in this case the pilot is fine. So its a) External ( test incoming electrical supply). b) The thermostat (does it click on and off? - is power sent to the gas valve solenoid). c) The gas valve/solenoid (they can sometime still be heard to click but not pass gas).
This is a low tech boiler. The only electronics will be an RF supression cap.
A replacement thermostat if you can track one down is sub 20. A replacement gas valve would be sub 100.
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The FAQ for uk.diy is at http://www.diyfaq.org.uk
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