Baxi 105e Fan/Flue fault led flashing

[robbierazz]

Hi Chris,

Ok, I will check the electrolytics. I have an ESR meter at work so can test them with that, after checking that they are discharged of course!

Interestingly, last night after the system had been switched off for a while, I tried powering up the boiler again and it worked ok again for about 10 seconds, i.e. the flame LED lit and the boiler fired up, but then the Fan fault LED started flashing again.

Anyway, now I can safely rule out a blocked venturi or flue, I guess it could only be the aps or pcb that are faulty. Would it be ok for me to connect the switch wires to the aps together temporarily and see if the fault then goes away, in order to determine for certain whether the aps is being activated properly? If so, should I connect the Common and NO switch wires together?

I have booked this afternoon off work so I can go home and have a look at the problem in more detail, so any tips/troubleshooting advice would be greatly appreciated.

 

[robbierazz]

Hi Chris,

Just thought I'd let you know that I think I've solved the problem!

I tested the electrolytics on the PCB and they all tested fine. However, when I took the two 12V relays out of circuit and tested them using a 12V DC supply and an ohmeter, I discovered that one of them wasn't switching properly. I could hear a faint click when energising the coil but there was no continuity between the switch contacts.

Anyway, I managed to find a similar spec replacement, although it was only rated at 3A. The original one was rated at 5A. However, the replacement one has two sets of contacts so I just paralleled them up to give me 6A total contact rating. I then had to fit it to the PCB using slightly extended wires as the pinout is different to the original.

I then refitted the pcb to the boiler and swiched on and hey presto! It now appears to be working fine!

Many thanks for all you help and suggestions and hope my discovery may be of use to you and others in the future.

Thanks,
Rob.

 

[robbierazz]

Hi Nick,

Have you checked over the dud pcb's that you have yet? Just wondered whether it's true about the relays being a common fault.

Thanks,
Rob.

 

[Aiky]

Hi Robbierazz,

looks like I have the same problem as you, can you tell me which relay to replace pls, can't stand the idea, or the cost of having to buy a new PCB for a perfectly good boiler that cost an arm and a leg to fit in the first place!!

All help gratefully received.

Aiky

 

[DP]

I wonder how your home insurance company will react should the boiler be the source of fire that destroys your house.

Baxi certainly will be pointing the accusing finger in your direction for 'tinkering' with the pcb/ installing components that are out of spec.

 

[ChrisR]

I'd be interested to know what the relay does - ie which one it is, too.

Unfortunately you can;t just parallel up relay contacts. One will always touch or break before the other so that one will stick or burn, then the other one!
"I could hear a faint click when energising the coil but there was no continuity between the switch contacts. "
..makes me think the contacts might be welded together. It would be typical of Potty to not do much to protect the relay contacts - spike caching diodes, snubbers etc.

I'm sure I have a couple of dead examples of those boards in the junk box - you know , the white dirty thing with 4 wheels on.

 

[robbierazz]

Dp, I'm sure that Baxi would love nothing more than me to shell out 100 odd quid on a new PCB every time a 30 pence component fails! The fact is the PCB quite clearly isn't 'fit for the purpose to which it was designed', as there should have been at least a snubber network protecting the relay contacts. This smacks of costcutting on Baxi's part to me, as it would have obviously cost them an extra few pence to integrate the said snubber network!

As an electronics engineer I would 'never' fit a component that was an inferior spec to the original. I fit at 'least' the same spec or better. The fact is that the replacement relay has a rating of 6A, whereas the original was 5A, so what's inferior about that then?

Against my better judgement, I am actually going to order an exact replacement relay, i.e the same as the original in every way. This is to keep the beaurocrats happy! The 'fix' that I've done was only meant to be temporary to enable heating and hot water to work again whilst waiting for the new relay to arrive. No doubt, this means that I'll be replacing the relay again in two years time, but such is life! I certainly am not going to pay for a brand new PCB every two years or so!!

Chris, I see your point about not connecting relay contacts in parallel, but I have done this many times during the course of my work, and have yet to have a failure occur! However, if you know of any real life examples where this has happened that I'd love to hear about it as it is certainly feasible that it 'could' happen.

Thanks,
Rob

 

[robbierazz]

Dp, following on from what I've already said, if I were to replace the relay with one that is the same spec, i.e. same coil resistance, coil voltage, and with 240V rated contacts, but with a current rating of 10Amps instead of 5Amps, as the original is, would that in your opinion be considered suitable?

The point I'm trying to make is that the replacement relay would then not be an 'exact same spec' replacement as the original, but surely would be 'even' better with 10Amp contacts rather that 5Amp?

I know that 10Amps may be a bit over the top for the load that's being switched, in this case the Fan, but it would surely mean that the contacts are likely to last longer due to them running well within the max current being drawn by the fan.

I would be interested to know your views on this, and would like to make clear that I was not trying to be clever with my previous reply to you, as you do have very valid points. It's a sign of the times nowdays though that there's too much beaurocrasy in life and not enough time to just get on with the job!

We get this problem all the time where I work, forever filling in Risk and Coshh assesments just to keep the insurance company happy!!

Thanks,
Rob.

 

[Agile]

As an electronics engineer you should know that the current rating of the relay is not determined by the current taken by the fan as thats less than one amp.

Its partly the initial surge when mains is applied to the static fan motor coil which could be 6 A. But mainly its the reaction of the contacts to disconnecting an inductive load when there is no snubber circuit.

These relays are rated for a resistive load !!!

My view is you could do no better than using a Finder relay as they have chunky silver contacts and I have never seen one fail in a boiler yet. Yes they cost about £4 each compared with about a pound for the cheap Chinese ones but yuo are paying for a quality component.

Tony

 

[robbierazz]

Hi Tony,

Yes, I am well aware that relay contacts are usally rated for a 'resistive' load, I mean, I studied the theory enough when I was at college! I am also aware of intial motor turn on current being higher due to the surge of current required to start a static motor.

The point I suppose I was trying to make is that putting a relay in with higher current rated contacts can only help and could possibly prolong the life of the relay too.

Anyway, I am intrigued about the relay that you mention and would be quite happy to pay 4 quid for a component that was going to last, so could you please advise where I might obtain such a relay?

Are they pin for pin compatible and do they have the same footprint as the original?

Many thanks,
Rob.

 

[robbierazz]

Hi again Tony,

Following on from my previous post, do you know if the Finder relays are available in Standard single pole configuration? I have only seen NO or NC changeover types, which are different to the original one used on the PCB.

Incidentally, I have seen some relays that give two different current ratings on the data sheets, one is a 'continuous' rating and the other is a 'maximum' rating.

Thanks,
Rob.

 

[ChrisR]

if you know of any real life examples

Saw many when I was in electronics industry. Fault reports from the QA depts were always interesting, & I got to be an itinerant consultant sorting out other people's design problems for a while - needed to be a bldy diplomat.. . Obviously there are lots of failure modes for relay contacts, but burning due to arcing on disconnection of inductive loads was often a problem. You need solid contacts for those, not gold plated, for example. It's a while ago now though, and I've forgotten a lot of the details.

Alarm bells should ring if a component apparently offers something for nothing. If a relay has the same power coil but claims higher current handling, it'll probably have bigger contacts (if the same material), so the contact pressure will be lower, and inferior in some apps. As you've pointed out, there are many parameters involved in switching.

Not that there's anything very demanding in a boiler, except the desire to use the cheapest and nastiest parts!
Which relay was it, and did you work out what it does? I doubt it's the fan relay?
I have a new version board (5112380) I can look at to see if they changed the relay which performs the same function.

 

[robbierazz]

Hi Chris,

If it doesn't switch power to the fan, then I'm not sure what it's switching.
I assumed this as the fan wasn't working before I replaced the relay. But I suppose it is complex due to being a closed loop system, i.e. the fan not receiving power until another valid signal has been detected elsewhere in the system.

If I'm perfectly honest, I didn't really try and trace what was being fed by the faulty relay, I just discovered that it didn't work and replaced it.

I can tell you that on my board there are two 12VDC relays next to each other and it was one of those that had developed a fault.

I've looked on e-bay recently and seen a few of these boards for sale, most of them sold as faulty for reconditioning purposes. I think it's awful that such cheap and nasty relays have been used meaning, for most people, replacement of the PCB every couple of years or so!! I'm not necessarily saying that the relays are at fault on all the 'dodgy' boards for sale on e-bay though.

Sorry I couldn't be more specific about the exact relay, but hope you can deduce from what I've told you, as I'd be interested to know what relays the new revision board have on them.

I did notice with interest that a work colleague of mine had his PCB replaced in a Potterton boiler. PCB was made by honeywell and all of the relays were 24VDC coils! Otherwise, the board looks identical to mine!

Thanks,
Rob.

 

[Bluebook]

Hi . Please help I seem to have the same problem (Fan or Flue fault code)

The flue seems visually clear and fine. However when I run the hot tap I notice that the fan isn't even moving.... Does this mean it is the PCB? IS there anything else I should check? Could it be a relay?

Having recently separated I really cant afford hundreds of pounds. Can anybody help please? thanks