Just as Christmas is approaching - I have the red light coming on (not
flashing) on my 7 year old boiler.
I have the installation instructions with the fault flow diagrams but am
still having a problem isolating the fault.
The story so far:
Last week came home after a few days away to find house cold and light
on, reset by turning boiler temp knob off and on, boiler fires and works
for some days before having the same symptom.
Resetting always seems to cure the fault short term.
I have only managed to see it go into its fault condition once, so I am
not sure exactly how the boiler was behaving!
But I think there was power and the gas valve was opening.
Going down the flow diagram I checked:
the condensate trap was not blocked
the fan was running
I checked the spark probe and found the wire jus pulled out of the probe
so changed spark & detection probes
I then decided to remove printed circuits, clean around the HT areas and
relay contacts and re-assemble just in case I could make the fault get
better or worse!
It seemed to be OK fot about 3 days but stopped again last night!
The problem seems to manifest itself after long periods of in activity
so is it still possible that its the connections on the trap?
I assume its the acid in the condensate that lowers the resistance
across its terminals.
Buying a new board is out of the question as I would have to buy a new
pair with wiring that cost approx £600 + vat!!
Does anyone know where I could get a circuit diagram for one of these
Any other advice welcome - sorry its a bit long!
Did you check the spark gap 4mm when replacing the ign
You can >temporarily< remove the earth lead to the
Condensate trap to test if this is a problem.
Was there any sign that the combustion door seal was leaking,
very common fault.
> Does anyone know where I could get a circuit diagram for one of these
> ignition pcb's?
> Any other advice welcome - sorry its a bit long!
> Happy Christmas
I had a similar problem a couple of years ago - turned out to be the
Ignition PCB - which I repaired. To do so I reverse-engineered the
PCB and drew a circuit diagram. Its a bit of a mess, but readable. I
could send you a scan of it in .pdf format if you wish (4 pages).
I also did a write up of how the circuit works - I could send you a
copy of that too (Word format).
Finally, I built a test set to test the Ignition board in isolation
(and also one for the Control PCB). If you are prepared to drive to
Maidenhead Berks, I would be happy to test the PCBs for you.
First in reply to John, I did check the gap of 4mm was OK.
Its just so intermittent!!
how would the combustion chamber cause this problem or was this just
(sorry did not want split thread)
> I had a similar problem a couple of years ago - turned out to be the
> Ignition PCB - which I repaired. To do so I reverse-engineered the
> PCB and drew a circuit diagram. Its a bit of a mess, but readable. I
> could send you a scan of it in .pdf format if you wish (4 pages).
> I also did a write up of how the circuit works - I could send you a
> copy of that too (Word format).
> Finally, I built a test set to test the Ignition board in isolation
> (and also one for the Control PCB). If you are prepared to drive to
> Maidenhead Berks, I would be happy to test the PCBs for you.
It might come to that, I am along the M4 south of Bristol and if its
going to help prevent purchasing a new boiler, it may well be worth it!
The problem is that it works most of the time so unless you know
pass/fail input/outputs levels it would be difficult to isolate the
problem as it may be just on the edge of its spec.
I would be very grateful for any information. Almost any format would
be OK as I have a Linux box.
As you seem to have investigated the circuits, do you know what sort of
resistance should be at the trap with and without the trap being full?
I can then simulate that input to see if it responds correctly. I will
however remove the earth lead and see if this has anything to do with it.
Out of curiosity, what was the fault on your pcb?
Thanks for your time
>Buying a new board is out of the question as I would have to buy a new
>pair with wiring that cost approx £600 + vat!!
I just noticed that my website must be out of date
I do them for IIRC £30 or £40
> Did you check the spark gap 4mm when replacing the ign
> You can >temporarily< remove the earth lead to the
> Condensate trap to test if this is a problem.
> Was there any sign that the combustion door seal was leaking,
> very common fault.
How would this cause the Ignition lockout fault?
The story continues!:
I thought I had cured the fault by cleaning the earth on the trap/flame
detector which was not perfect.
The boiler has been OK for six days then failed twice yesterday.
The good thing was that I have now seen the exact symptoms. I had
thought the fan and gas were OK but have now found that the reason there
is no flame is that the gas valve did not operate. it then tries 4 or 5
times to fire then goes into lockout.
I now need to check connections and the ignition circuit to find which
pcb(s) are involved.
Are solenoid valves relatively trouble free or do they give problems
often? (OK I know this is a "length of string" tye question but would
My valve has about 4 wires so its not just one coil!
Happy New Year
Correction the circuit only shows 2 wires plus earth, but on readind
the fault diagnosis further it says: Check sensing tube (in/on gas
valve). Can someone tell me where this is please as I am having trouble
> Happy New Year
> Peter Hemmings wrote:
> Correction the circuit only shows 2 wires plus earth, but on readind
> the fault diagnosis further it says: Check sensing tube (in/on gas
> valve). Can someone tell me where this is please as I am having trouble
> finding it!?
This would be the casing pressure pipe as shown in Fig 58 in the manual.
If it comes off or gets blocked the gas/air ratio will be seriously
affected. To lean and it won't light. To rich and the burner will soot
I haven't been following this thread.
My instinct is to say it's a Barcelona how much is it worth to try and
keep it alive?
The electronics uses the ignition wire in three ways which can't help.
1) HT spark ignition. 2) Flame sensing. 3) Condensate trap.
The latter is sensed by the wire being earthed if the trap fills.
In my experience the trap is apt to become dry and overheat on this model.
In later models the condensate trap switch was omitted (?!) and the wire
left loose to incidentally short to ground.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
> I haven't been following this thread.
> My instinct is to say it's a Barcelona how much is it worth
to try and
> keep it alive?
> The electronics uses the ignition wire in three ways which
> 1) HT spark ignition. 2) Flame sensing. 3) Condensate trap.
The Barcelona has a separate flame sensor probe that goes to
pin 4? of the ign pcb.
I may well be wrong, although there have been a complete redesign of the
PCBs for this unit.
Anyone care to throw some light on what a "sensing tube" actually is!?
Is this the probe or something in or on the gas valve for instance.
The really sad thing is that it seems to now go for 5 to 6 days without
you say you do the pcbs for this model? This boiler is brill but sadly
let down by the electronics side of it.
I worked at the foundry that made the exchangers so i managed to blag
a full set of spares for the thing! needless to say i have needed most
i think one set of pcbs has different characteristics to the other
(slightly less reliable) and i have managed to keep the thing going by
swapping bits as and when for the last 8 years or so.
I have just got to the point where i have nearly had enough and am
ready to throw it through the window!
I am willing to give it another chance by changing the pcbs:-
can you tell me if the new models are upgraded/modified? if so has got
to be worth a shot what do you reckon?
My boiler was one of the first i think so things can only have got
If you could let me know prices etc. that would be great, also very
handy to know when im changing other boiler pcbs and stuff.
Thanks for your help, and happy new year!
The flame sensing wire checks electrically that gas has lit.
The sensing tube relays the air pressure inside the room sealed part of
the boiler to the gas valve. The manual refers to this as the casing
I've read the OP. Is there any indication as to the type of lockout?
Assuming it's ignition failure and it happens when the boiler has been
idle for a while this would make me think of damp.
In principle the burner should be dry and the condensing happen in the
deeper (back part) of the heat exchanger.
What I do is a one for one exchange (if I have stock)
>My boiler was one of the first i think so things can only have got
>If you could let me know prices etc. that would be great, also very
>handy to know when im changing other boiler pcbs and stuff.
>Thanks for your help, and happy new year!
Don't know whether you guys understand the cause of failure of the
ignition and control PCBs? I have some history with Baxi Barcelona -
had one of the first I think (September 1997). Had 6 incidences of
failure and board replacement, and got into big dispute with Baxi over
the design fault. My boiler is installed in a cupboard. Whenever I
turned up the stat, (during the winter), or shut the door on the
cupboard, a few days later I would get intermittent ignition lockout.
Then a few days later it would fail solidly. I figured all this
pointed to overheating of the electronics. I compared the electronics
module of the boiler with the mother board in a PC - no active cooling
on the Baxi, while it is sitting next to ( and bolted to) a 35KW
My solution, by the way, which is now 3 years old and completely
successful, was to stuff the pipe of a standard shower ventilation fan
into the front of the electronics module, and suck 70L/min of air over
the boards. I also pulled the module case away from the mainframe,
drilled some holes in it, and putting spacers in so that air would
flow through and over the circuit boards. The fan is hooked up to the
main controller so that it comes on with the pump, and has a delay so
that it keeps going for a minute even after the boiler has switched
off. It is not elegent, but totally functional, which the original was
Thanks, I hadn't realised the PCB were over eating so much. (although
putting the electronics at the top of the boiler obviously helps the
Another far from ideal feature of the design is that every boiler demand
is a full mains power switch from 'cold' for the electronics. This design
was presumably so that the boiler would have the same wiring complexity
as a cast iron floor mounted design...
>Thanks, I hadn't realised the PCB were over eating so much.
Well don't let it stay in the kitchen .. it'll get all porky and fur up;)..