Baxi 105e Fan/Flue fault led flashing

robbierazz · 29 Jan 2007

Hi There,

I have just attempted to run some hot water from a tap and noticed that the water wasn't coming through hot. I then checked the boiler and found the above led is flashing?

Any ideas on what I could check? Could it be a loose connection on a sensor or something?

Please help as I currently have no hot water or central heating.

I have a multimeter so can test for voltages if necessary.

Thanks,
Rob.

baxpoti · 29 Jan 2007

Tried re-setting?
Check flue, fan, venturi, air tubes and aps
Then change the circuit board!

robbierazz · 29 Jan 2007

Hi baxpoti,

Yes, I reset the boiler and it worked ok again for about 10 minutes and then the fault reappeared.

Should the fan be on all the time? I will take panel off and see if it is running and also check to see that it is receiving power. Just need to know whether it is supposed to run all the time or not?

Also, what's best way of checking flue?

I have heard that some models of this boiler have dodgy circuit boards fitted and Baxi have released a modified, more reliable version now. How can I check whether I have one of the so called 'dodgy batch'?

robbierazz · 29 Jan 2007

Hi again,

I have removed the 4 screws from the inner door panel but it doesn't want to budge. Any ideas??

Obviously, I can't check the fan until this comes off.

baxpoti · 29 Jan 2007

robbierazz said:
Should the fan be on all the time?

When there is a demand for heat

robbierazz said:
what's best way of checking flue?

Visual inspection

robbierazz said:
I have heard that some models of this boiler have dodgy circuit boards fitted and Baxi have released a modified, more reliable version now. How can I check whether I have one of the so called 'dodgy batch'?

Don't believe everything you hear!

baxpoti · 29 Jan 2007

robbierazz said:
I have removed the 4 screws from the inner door panel but it doesn't want to budge. Any ideas??

Just ease it off from the bottom, it's just stuck, literally, and lift, as per the outer case.

ChrisR · 29 Jan 2007

ROb the old one you have is 248074 and the new one 5112380.

robbierazz · 29 Jan 2007

Hi There,

I have checked the fan and it doesn't spin when there is a call for heat, thus resulting in the Fan/Flue fault led flashing.

Could this be due to a faulty aps? Am just about to check it out of circuit for continuity.

robbierazz · 29 Jan 2007

What's the best way to check for correct operation of the aps?

I have removed it from the boiler, making a note of where the pipes and connections go of course!

robbierazz · 29 Jan 2007

Hi There,

Have just checked operation of the aps micro switch and it appears to work fine. I've check both the NC and NO terminals.

Any ideas??

I have a feeling I'm moving towards replacing the dreaded pcb, unless I can find a fault elsewhere. Could you explain when and how the aps is activated so that the microswitch will switch positions? What are the pre requisites for this to happen?

Just trying to figure out if the fan isn't working before of the aps or vice versa.

Should I check the PCB to check if there is 240V to the fan when I've swtiched heating to constant?

If there isn't then the problem must be the PCB I guess.

Thanks,
Rob.

Agile · 29 Jan 2007

Assuning you have a system flow switch have you checked to see if this activates reliably and stays that way?

robbierazz · 29 Jan 2007

Hi There Agile,

I have checked and there is no power to the fan when heating is switched to constant even though I hear a relay on the PCB switch as soon as I switch to constant mode.

My question is, could a blocked venturi prevent the PCB from applying power to the fan, or should there at least be power to the fan regardless of whether the venturi is blocked or not?

Could you explain how to check the venturi to see if it is blocked?

Also, what do you mean by 'system flow switch'? Where would this be located if the Baxi 105e has one?

Does the lack of 240V at the fan terminals when there is a demand for heat necessarily mean that the PCB is shot?

I have noticed that the fan turns ever so slightly when there is demand for DHW, almost as if it is trying to start up properly but can't. I've tried to measure the voltage at the fan terminals when this happens, but due to using a digital DMM means that it seems to happen too fast to register on the meter what's happening. Does this provide any clues??

ChrisR · 30 Jan 2007

I have noticed that the fan turns ever so slightly when there is demand for DHW, almost as if it is trying to start up properly but can't. ....... Does this provide any clues??

Yes.
PCB

robbierazz · 30 Jan 2007

Hi, thanks Chris.

I am actually an electronics engineer by trade, although I also dabble in electrics quite a bit as part of my job.

Anyway, I have removed the PCB and will check out what components I can with a multimeter to see if I can find anything obvious wrong. I have heard that the relays are prone to failing on this model board, so will check them out also.

Could you just clarify something for me though. I assume that the pressure switch will only work if the fan is spinning, due to the pressure only being detected by the switch if there is airflow generated by the fan?

Now, bearing in mind that the fan is not working when there is a demand for heat, combined with the fact that there is no power to the fan either, can I safely dismiss the aps or a blocked flue/venturi as a possible cause of the problem?

I am happy to replace the PCB if it 'does' sound like it's 100% the cause of the problem, but don't want to spend 80 quid out if it doesn't solve it, even if I do end up with a shiny new pcb!

Many thanks everyone for all your help so far.

Thanks,
Rob.

ChrisR · 30 Jan 2007

Well it isn't the venturi if the fan isn't running yet

The boiler will probably check that the aps is not already closed before it applies power to the fan, so you could check that. Sometimes the aps changeover contacts are used, some just go on the logic. LIkely to be 24V, by the way.
Usually in the circuitry on a pcb there are delays built in around the fan/aps department, because the low pressures can take time to build and fall, and the fan needs time to spin up and down. That makes me think it's likely to be a capacitor failing. Often they use electrolytics very near the voltage rating of the cap to save pennies, so they break down. These boards seem to fail at just a couple of years old, too.

Please do find which it is! I've got old and new boards to compare, and a dud old board or seven, so I ought to be able to do it myself, but...
The other possibility is always a cracked solder joint, likely to be at a relay leg or connector. If you can be bothered, try resoldering them all!

They always seem to fail in the same way, and the boards for the Instant version (248731) do too. Interestingly baxi haven't replaced that board, so a comparison of old and new of those boards might show up the change...

diynot

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Baxi 105e Fan/Flue fault led flashing

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