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Plumberpro
Plumberpro, Plumber
Category: Plumbing
Satisfied Customers: 634
Experience:  Heating and plumbing answers. 20 years experience
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, I have a Biasi M90 24S combi boiler. Over the past few

Resolved Question:

Hi, I have a Biasi M90 24S combi boiler. Over the past few months the hot water was fine but the heating would turn off after an hour or so and not re-fire, the light would flash fast and the pump and fan continue to run. If you switched the heating off for a couple of seconds and back on again it would re-fire no problem (whether system was hot or cold)so we didn't worry about it as the boiler is quite old. This has got much worse recently. I added some Sentinel cleaner/sludge remover last weekend and drained it yesterday, then added some descaler. At the moment, if the system is cold, the boiler (or hot water) will fire up no problem but only lasts for 2 to 5 minutes for both heating and hot water. If youy try to turn it off and on it doesn't work and you have to wait about 30 mins before you can start it up again. Any ideas would be great!

Update - I have put it into service mode and found "Lack of burner ignition (no ignition signal from the full sequence ignition device)".

Any ideas?

Submitted: 2 years ago.
Category: Plumbing
Expert:  Plumberpro replied 2 years ago.
Plumberpro :

Hi . first thing to do ius change the hot water and heating thermistors( temperature stats) . when these start to go on these boilers , all hell breaks loose.. Very common on these to fail , cheap and easy to fit. I carry spares with me as you can guarantee they will be needed at some point

JACUSTOMER-n3gvoih3- :

Hi, thanks for the reply. I've changed both thermistors and it worked for about 20 mins which is better than before but now it's gone back to how it was before. Any other ideas? Same fault lights, fan and pump run but won't restart. Any other ideas?

Plumberpro :

Hi . I take it you have pressure above 1 bar?

Plumberpro :

Hi ,I've got the led fault codes ,

Plumberpro :

3 LEDs , what one flashes , and what are the others doing , ie on off

Plumberpro :

.

JACUSTOMER-n3gvoih3- :

Hi, the pressure is between 1 and 2 bars. After replacing the thermistors it runs for longer than before, about 10 minutes, then cuts out. This is the same for both heating and hot water.

JACUSTOMER-n3gvoih3- :

The LED's in service mode are: right and left green flashing, central red on all the time.

JACUSTOMER-n3gvoih3- :

In the manual those lights indicate "Lack of burner ignition (no ignition signal from the full sequence ignition device)".

Plumberpro :

Hi , that fault code means no ignition detected. The boiler has a flame rectification ( detection probe) that recoidnises when the burner is lit. If the probe is faulty the boiler would normally try to relight again before going to lock out . does our do not that?

Plumberpro :

Sorry , meant does yours do that ?

JACUSTOMER-n3gvoih3- :

Hi, I don't think that's it but could be wrong. When you switch it on there's an immediate click, the fan and pump engage straight away. There's also a click form the ignition PCB, then a click somewhere central around the gas valve, then a click on the diverter valve and it fires.

JACUSTOMER-n3gvoih3- :

I just stood in front of it while it was working, there was a click from the right PCB and the flame went out, then it immediately re-fired but only lasted for about 30 seconds, then the flame went out, fan & pump still running and went to lock out.There didn't seem to be any attempt for it to re-light itself.

JACUSTOMER-n3gvoih3- :

I just ran the hot water, started up fine, ran for about 3 minutes and there was a click from the right PCB and the flame died, it immediately restarted then the same thing happened about a minute later. It then ran for a few more minutes, enough time to fill the bath before cutting out completely and going to lock-out.

Plumberpro :

Hi . pretty sure its the flame detection probe . easy to change

Customer:

Thanks, ***** ***** if I can pick one up and get back to you.

Plumberpro :

Your welcome .

Customer:

Hi again, There's been some success but it's not 100% fixed. I changed the detection probe yesterday and while I was at it also changed the overheat thermostat, cleaned the combustion chamber, cleaned the fan, venturi and checked the venturi tubes. It's now running much better thanks to your advice, there's no problem with hot water for baths & showers but the heating will cut out in the same way somewhere between half an hour and an hour after being switched on. The symptoms are then the same, lock out, LED flashing fast, fan and pump running. I put it into service mode and the LEDs were the same as before, central red on all the time, outside greens both flashing which indicates "Lack of burner ignition (no ignition signal from the full sequence ignition device)".

Customer:

So far the following has been done: System cleaned, water running clear, descaled and protector added to system, new thermistors, new flame detection probe, new overheat thermostat. I might take the ignition PCB out later and check for any dry solder, do you think this could be the problem or is there anything else I should try?

Plumberpro :

. I can now only think that PCB is at fault .

Customer:

Hi again, I'll check the pcb for dry solder joints and try to repair if possible. There's a new problem happening, whilst running there's a click from the ignition pcb then the fan keeps going on and off about every half second, same fault lights (this can happen after running for a couple of minutes or half an hour). If you try to restart it after that the fan does the same thing going on and off about every half second. Is this likely to be related to the same problem or something different?

Plumberpro :

Must be related to faulty PCB as it is controlled from there.

Customer:

Hi again, I fitted a new ignition pcb yesterday and it's been fine since then. Thanks very much for all your help.

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