Biasi M90e 24s - Boiler runs but no ignition spark

18 Jan 2007
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United Kingdom
Hello, please can you help. My five year old Biasi Riva Compact M90e.24s started playing up the beginning of this week and now there is no ignition spark when starting. When the central heating was working normal, hot water was supplied at the tap, but with the central heating not in use, if you wanted hot water at the tap, the boiler would run [you can hear the fan] but no ignition spark. Now, there is no spark produced for the central heating or for the hot water? The green light flashes quicker than normal.
The red lock out light doesn't come on unless you turn off the gas tap - the lock out doesn't act immediately.

I am a engineer by trade but not within the heating industry. I have read through the Biasi service manual for basic checks. The circulating pump is rotating as expected. The fan motor turns as expected. The system pressure is 1.3 bar when cold. I can't see any obstructions within the flue, etc. The service manual fault finder suggests the air pressure switch or ignition device.

The boiler was serviced Oct 06 and I'm sure a new central heating switch membrain was fitted July/Aug 06.

Can you help?
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Its good that you have given so much information because I suspect it points to the fault.

Unfortunately what you have said is a little conflicting and I suspect you may have got confused.

When the pump runs it SHOULD operate the system flow switch. The next sequence is to start the fan. You have not made it clear if the fan is being started but I suspect not.

Its VERY rare that the diaphragm nees to be replaced so I think this was done when it was not necessary. Much more common is dirt in the diaphragm chamber!. Or sometimes the injector screw is too far out and needs screwing back in.

You can see if the switch is being operated by the pin and report back.


EDIT You other spam posting says the fan is not operating. If that is the case then the air pressure switch is not being operated to advance the ignition sequence. Check flue test point plug is in place. Then that the flue is not blocked or damaged.

If its fan/APS problem then it starts to be CORGI territory. Are you in Clapham Terrace ?
Thanks for your help Tony.

Right, just turned the boiler on, system flow switch pin has come out and pushed against the by-metal strip. Pump is rotating and I can hear the fan running at speed. The green light is flashing faster than normal.

What's next

Regards Steve
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If that is the case then the air pressure switch is not being operated to advance the ignition sequence. Check flue test point plug is in place. Then that the flue is not blocked or damaged.

If its fan/APS problem then it starts to be CORGI territory. Are you in Clapham Terrace ?

Its not that in this particular case because he has now said the fan is running. Or was that his wife?

Hi Tony,

Forget the wife - she's logged off and gone to bed.

The fan is running - boiler doesn't start. Turn the control switch to summer setting, turn the hot tap on - fan is running - boiler doesn't start.

When the boiler worked okay. you would hear the boiler run when switched on and see the spark jump between the electrodes before igniting - now there is no spark.

No flue obstruction. The vacuum pipes to the air pressure switch are good and I've also blown through the venturi and fan jet. Pressure point caps are secure. Can't see any other points for vacuum loss.

I've found out how to check the the Air Pressure Switch electrical resistance between the connections - which I will do tomorrow.

Any other ideas/suggestions?

Regards Steve.
NEVER blow into the APS!

Its a precision device and you will damage it! Just blow TOWARDS the +ve connection.

Measure the resistance of the C to the NC and then to the NO whilst blowing towards it. Should be less than 1 ohm.

Then you need to find out if the APS is really being operated by the fan!

As a very last resort check the O/H stat has continuity. Its on the right hand side of the main heat exchanger but rarely fails.

If the APS is making when the fan starts then I am afraid it sounds as if its the ignition PCB failed. This will cost about £75 or so.

Went to one of these last week and it was indeed the ignition board! Quite easy to change though.
Okay - fixed it.

Found no power supply to the air pressure switch - no continuity through the wiring loom. Soldered three new terminals to the switch and okay.

Well done.

It sounds as if the female spade connector on the "C" terminal had a faulty crimped connection to the cable.

With all the money you have saved you can take the wife out for a meal to the Castle Balti !

On the left when you take the cover off the system flow diaphragm housing.

You can even see the domed part which covers it on the outside which acts as a clue to what you may find if you can get your hands onto the inside.

I had the same problem with my biasi m90e.32s

It turned out that the contacts to the fan were dirty.

Some cold cleaner electrical contact cleaner on the points of that and also the air pressure switch, left for 1/2 hour and it works again. Hooray!

Think I will take it apart and so a hard clean of the points and reassemble just for peace of mind.

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