WB 24CDi Burner Lockout

My Worcester Bosch 24CDi combi boiler keeps occasionally entering its
'burner lockout' state. The problem is so intermittent that resetting
the boiler always brings it back to life and I have so far been unable
to observe/determine whether the boiler is entering this state as a
result of it failing to ignite, partial ignition, igniting but failing
to detect the flame or the flame extinguishing when it shouldn't.
In the hope that it is either the spark electrodes or flame sensor
that are to blame (i.e. not a more complicated/expensive cause like
the control board, gas valve or gas supply etc) I purchased
replacements whilst it was convenient to obtain them (and negligible
cost too).
Can anyone tell from the following photos whether it looks like the
spark electrodes and/or flame sensor are in need of replacement? I
appreciate it may be hard to tell given that most of the time the
boiler works fine and so if either is to blame it must be due to a
borderline condition.
formatting link
have verified the correct gaps (3-4mm spark electrodes and 5-6mm
flame sensor) and the boiler is at least 5 (possibly 7 or more) years
old now if that helps.
Unfortunately the replacement of the flame sensor requires the removal
of the burner, i.e. disconnection from the gas valve, and I didn't
feel competent that I could ensure (through testing) gas soundness of
the reconstructed burner/valve union. That said, how would one test
the soundness given it is on the low pressure side of the valve?
I replaced the spark electrodes anyway given I had the part and,
whilst I may be imagining this, the new spark certainly seems more
pronounced.
I am now keeping an eye on the boiler in the hope that it is either
now fine or I will catch it in the act of entering the burner lockout
state so I can determine at what stage it occurs and hence rule in/out
potential factors.
Any thoughts/opinion would be most welcome.
Mathew
Reply to
Mathew Newton
In message , Mathew Newton writes
Well, that's the crux. isn't it
Check the flame sense lead - physically give it a bit of a tug
Reply to
geoff
I think I may be getting somewhere... but it's a place I don't like...
I managed to catch it in the act today - the stat called for heat, the pump/fan activated and the electrodes started sparking but nothing else. After 10 seconds or so the boiler gave up and entered burner lockout.
I am assuming the valve did not open, or is its mode of operation more complicated than this?
The service manual fault chart says that if resistance across the two sets of wires to the valve (main valve connections as opposed to regulator according to the book) is not
Reply to
Mathew Newton
I forgot to mention; if you can this a 'test' I did confirm the gas supply was okay as the hob is working (I'm sure there's more to a supply than that though).
Mathew
Reply to
Mathew Newton
Well... I've moved on now.. and I'm *definitely* in a place I don't like.
A few years back I replaced the control board following some problems with the overrun not working properly (pulsing fan). I forgot that I'd kept the old board so I've just fitted it and... occasional burner lockouts.
So, I'm assuming it's the gas valve so will get someone out to replace it. I'm not comfortable doing it myself, not least the setting pressures aspects.
Cheers,
Mathew
Reply to
Mathew Newton
In message , Mathew Newton writes
Have you measured the volts on the gas valve when it's sparking ?
When it's sparking the GV has to open
That would, IMO, be an obvious thing to do
volts to valve - valve problem
no volts to valve - pcb problem
Reply to
geoff
In message , Mathew Newton writes
Just a minute, as I read your post
new board - boiler doesn't fire
old board - boiler fires sometimes
Take one step back, and reassess your deductions
Reply to
geoff
Sorry, perhaps I wasn't clear. Both boards fire most of the time...
I haven't checked the voltage at the valve - I simply can't get round the back of it to do so!
I've now booked a Worcester engineer for Friday - it's a flat rate fee of =A3185 inc. labour, VAT and upto 2 major parts (exc. heat exchanger). I figured that if it's either the PCB or valve then I'm reasonably happy with the price, particularly given they ought to be able to fix it and ensure everything is hunkydory. I'm a little worried about when he sees my new spark electrodes - do you think they'll kick up a fuss given I've been 'meddling'?
Thanks for you advice so far, it's just a shame I'm not managing to pinpoint the problem myself even with it.
Mathew
Reply to
Mathew Newton
In message , Mathew Newton writes
Ah - I thought it was the other way round
Do you need to ?
measure it on the connector on the pcb
This introduces loom wiring as an unknown, but on a relatively new boiler, it shouldn't be a problem
Reply to
geoff
True. I'll give it a shot tomorrow.
There are six wires to the valve - 2 x blue for 'regulator', 2 x brown for 'main' and another 2 x violet for 'main'. Given my testing time is limited (intermittent fault, 10 second window) can you advise on which I ought to be concentrating on? It would help if I knew the principle of exactly how the valve works but Googling failed me.. (or rather I failed it!)
Given the service manual speaks of measuring the resistance of the two 'main' pairs (brown and violet) so I'm assuming these are two solenoids? (why two?) What does the regulator consist of?
Sorry for all these questions, I'm sure you must be doubting my competence but I just want to understand as much as possible to get the most of this situation.
Mathew
Reply to
Mathew Newton
In message , Mathew Newton writes
ITYF the two main valves are a two stage main valve - 240 volts
the "regulator" is what's known as a modureg, it's a 24v modulating valve which adjusts it's flow rate according to the voltage on the solenoid. It's purpose is to fine tune the output depending on the demand so that e.g. you get a constant temperature hot water irrespective of the flow rate through the tap
Reply to
geoff
Thanks for that - very useful.
I gave this a shot this morning and found that, during (attempted) ignition the voltage across each of the main valve points on the PCB (MV1 and MV2) rose to 135v AC (I suppose it could've been on its way to 240v AC but the digital meter update refresh may not be quick enough) and this coincided with a small thud from the valve. During the 10 seconds of sparking the voltage remained steady at something like 15v AC. Does this sound right? It was the same for both valves points. At the end of the ignition period it gave up, the valve gave another small thud, the sparking stopped and it enter buner lockout.
Remember I am seeing the same issues with both boards, so I'm assuming it's definitely the gas valve. The small thuds I hear are worrying though - that to me suggests it is opening or is there more to the successful operation of the valve than that?
Mathew
Reply to
Mathew Newton
When we had a WB engineer he replaced the faulty item plus a couple of other things that "might go", so it was probably a good deal compared to a local engineer
Reply to
Stuart Noble
On 19 Dec, 10:50, Stuart Noble wrote:
That's good to hear - I was wondering how it might work, not least given =A3185 doesn't go very far when it comes to many boiler parts. I suppose it may depend on the engineer but I'll certainly try to ease the process with tea and choccy biccies. Might even train the cats to shiver too.
My biggest concern is that the problem won't manifest itself on the day. I've taken a video of it happening so hopefully that might help should this happen.
Mathew
Reply to
Mathew Newton
He came out today and firstly replaced the air pressure switch - not sure why. Anyway, that didn't sort it so he then put a new gas valve in. Job done... at least so far - I'll be absolutely gutted if I wake up tomorrow to a cold house!
Thanks for all your help Geoff - much appreciated.
Cheers,
Mathew
Reply to
Mathew Newton
I'd be interested to know if you get any kind of written confirmation from WB about what's been replaced and what kind of warranty applies to the new bits. I was given no paperwork at all and, although I have the bank debit and the original bits as proof, it's not a very professional way of carrying on.
They replaced a leaking pump on mine in March and the same fault appears to be developing again. I somehow thought it might because the auto air vent (which apparently often leaks, but costs tuppence and is easily replaceable ) is right at the back of the pump. Nice one, WB.
Reply to
Stuart Noble
We had a WB engineer in here this morning. He didn't leave a service report either. He said it was on his laptop and the office would be sending me a printed copy. We'll see.
We had also had an odd intermittent water leak on our 4 year old condensing boiler which came and went away. It came from a joint in the flue ! The engineer said whether it actually leaks or not depends much on patterns of usage inside / outside temperatures etc.
DG
Reply to
Derek Geldard
All I got as a follow-up was an invitation to take out a yearly service agreement. I think their long term plan is to leave you no other option. If their stupid £120 pump is going to fail annually because of a design fault, they would seem to have one by the short and curlies.
Reply to
Stuart Noble

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