Biasi Garda M90F.28S! Headache fault Agghhhh!

[Tunni56]

Ok experts, are you ready for a headache..or perhaps help cure mine and point out the fix. I'll try and keep this simple and precise.

The above boiler began cycling off and on and would not supply DHW unless CH dial was turned up (ie central heating on full)

This eventually led to the lockout/shut out light coming on. Once the reset was pressed the boiler would restart but do the above again and
supply DHW

Now, I have a few spares for this M90F boiler, so I decided to just swap out both circuit boards. The result was the boiler operated better but very similar to before. ie it still cycled off on but remained stable for a bit longer...confusing?... it gets worse!

To check the fan, I removed the combustion cover AND guess what.. the boiler WORKED perfectly!! DHW and Central Heating! I tested it a few times to make sure and yeh it worked perfectly. Then after replacing the cover the problem returned!!! BUT the lockout light now comes on and will not reset, whatever I do!!

I then tried reconnecting the old PCBs but the lockout light remains stuck on

So I am massively confused and frustrated. Something is causing the total lockout, that's for sure..but I'm not sure what.

The last thing I did earlier tonight was to undo the pump bleed screw and water gushed out which suggests a busted pump (pump spindle rotates easy) as only a few drops should trickle out so there's another possible fault. But I've no idea whether I've got multiple faults of just one...

I'm not sure where to begin due to the confusing results. I know there are proper experts on here who fault find all day long and I'd be very grateful or your input and advice.

Cheers guys!

BTW my dad was a plumber/heating engineer (long dead and RIP) I was sweating lead to copper joints using tallow, moleskin and a paraffin blowlamp over 45 years ago! For the record, I am a highly skilled and vastly experienced plumber but have never been CORGI/Gas safe registered, hope that doesn't stop anyone assisting me.

 

[picasso]

Taking the cover off and the boiler runs points to a problem with one of the air/flue components but we are not allowed to give advice on taking your boiler to bits, if its driving you that mad perhaps its time to get a fella in that knows how to mend boilers.

 

[pred]

The only problems I've had with Biasi was on an old x rated model, inside there's a small pipe going from the flu to a sensor and it was blocked with condensation, removed and a quick blow cured that, the other thing Biasi are prone to is the diaphragm becoming porous, takes about 10 minutes to replace. I've not had any problems with the condensing Biasi YET!! Touch wood..

 

[Agile]

Your boiler obviously has a gas/combustion fault and we are not permitted to give advice in this forum for DIY repairs by non gas registered people.

Those faults are very rare on the Biasi M90 which have common internal water flow and pcb faults instead.

The obvious solution is to call a competent boiler engineer! Although I suspect you may not want to do that.

Tony

 

[Tunni56]

The ignition board was causing the lockout! Despite having all the same connections it was a different board so I put the honeywell one back on and out went the lockout LED.

The boiler attempted to fire up but no spark/ignition. I poured over the manual and went through the ignition sequence and it pointed to the pressure switch or main board. But I'd swapped the main PCB and the pressure switch checked out OK using a multimeter. So I was baffled, eventually I changed the fan and venturi (as I had a spare) and the boiler fired up!!

There is still a fault though I only get DHW if the heating demand is turned up. I'm pretty sure that's a dodgy diverter valve which I'll sort tomoz!

 

[Agile]

The M90 used either a Honeywell or a Bertorelli ign pcb.

They are both completely interchangeable.

However, there is a slight difference between how they operate. One if you remove the mod coil connection it will stop firing and on the other it continues.

I am not permitted to advise you on gas issues here.

Tony

 

[Tunni56]

That's right Tony I have both boards, the Honywell one is the supposed unreliable one? and in fact I notice burn marks where several resistors have over heated and scorched the PCB...never a good design point!

The other board when fitted causes the lockout LED to light up so I have to assume it's faulty. Were or are they a better made board though?

Thanks for the input BTW