Biasi M90 24s intermittent fault

[Redspike]

I have been in my place for about a year and have a Biasi M90 24s boiler.
As far as I can make out it was installed in 2002 and I have receipts for a replacement PCB in 2003 and a replacement fan unit in 2006.
Over the past few months the water hasn't seemed as hot as it was and is not constant, although the heating is fine.
I've recently flushed the system through and added an inhibitor thinking that it may help the eficeincy of the HE plate.
This hasn't improved the water temperature and I have now noticed that the boiler is not always firing up. When it doesn't I get fast flashing green light. Diagnostic mode indicates lack of flow in primary circuit. (I can't be sure that this hasn't been happening for some time without us noticing)

Initially my thoughts were air in the circuit but I have bled and bled the system and have 1.5 bar on the gauge.

When it's not firing up I can't hear the fan running.

Checked the pump for obstructions.
Checked the operation of the primary flow switch, cleaned it and replaced the diaphragm in case.

When it fails, the pin on the primary flow switch doesn't extend fully and therefore doesn't operate the microswitch. If I manually operate the switch the boiler fires up and the pin then fully protudes.

The fault occurs on demand for DHW and Heat together or independently, although some times turning on a hot tap will enable the boiler to fire up when it has failed for heating.

As this is intermittent, can it be electronic (i.e Full sequence device)
or is it still likley to be air or some obstruction in the circuit?

I have searched previous similar posts but not found one with exactly the same fault detailed.

Any advice would be appreciated before I fork out unecessaily for an engineer or PCB.

 

[Agile]

If you are correct about the diagnostic code then you are fooling yourself because the pump is turned off if the flow switch is not operated within five seconds of the pump starting.

I usually find that the cause of inadequate flow is usually a failing pump or a blockage within the boiler. There are several variants of the cause and some can be difficult for many people to find without considerable experience of repairing boilers.

To have a failed PCB and fan on the same boiler is pretty rare as these are generally quite reliable boilers.

Tony

 

[Redspike]

Thanks Tony,
I am right about the diagnostic lights.
As I say the pump turns freely, and there was no sign of any debris when I opened it up. Are you saying it could be an intermittent fault with the pump, or is it worth taking of the HE plate to check for a blockage? Do you think that it is definitely a flow problem and not electrical?

The reason I ask is that I have been creating a fair bit of dust in the room from some building works. Is it possible that dust in the venturi device or APS would cause such a fault?

Again any advice or checks that you can suggest are appreciated.

 

[Agile]

Its not specifically the plate HE because you say it happens on both CH and DHW.

I expect that its an intermittent operation of the system flow switch.

However, its a boiler! So there could always be a PCB or electrical fault perhaps not always powering the pump or not recognising the flow switch is made! It just adds to the fun.

It could also be the microswitch but I discounted that because you said the pin did not come out reliably but then that may have been your confusion.

The pin should be fairly hard to push back with your finger without some discomfort.

Tony

 

[gas4you]

Tony, is this the Biasi that they make as the Ideal Mini?

OP if so, it is a very common fault on the mini that crud gets in the small waterways and stops the pin from poking out fully, thereby not proving the pump and not allowing the boiler to progress further.

Common cheap remedy for this is to place a very small bit of rubber in the microswitch to make up the short fall of the pin not coming out.

Ideal engineers on my patch have 'officially' said this is what they do.

 

[Redspike]

Tony,
I've watched it when it fails and the pin comes out but not enough to make the switch connection. I can push the pin in but it is nice and stiff.

Gas4you, I did consider adding something to the micro switch as suggests, or bending the lever on it to make it earlier, but seem to recall Tony saying this may cause damage in another post.
I did get some minor grit when I first checked the flow switch, but I've checked a couple of times since and nothing obvious is apparent.

Is it worth taking that whole manifold off and checking it for obstructions? Or is it safe to adjust the microswitch?

 

[Agile]

Same boiler Dave. It doesn't say much for the calibre of any Ideal engineer who cannot fix it without bypassing the problem.

I would never do anything like that except as a very temporary solution when I am already empowered to solve the problem.

It can do a lot of damage if anything goes wrong ( like burning down the house perhaps. )

It comes within the category of bypassing a safety device.

Tony

 

[Redspike]

Thanks Tony, clearly adjusting the microswitch won't find the fault, but I'm still not clear on the sequence of operation. Would an intermittent fault with the full sequence board, or some sort of poor connection with the fan, pump or other electrics really be able to affect the flow sufficiently as to stop the flow switch pin from fully protruding?
Sounds like I'll have to remove the flow switch again and give it another check and clean. Could an obstruction in that manifold with the diverter be causing some problem, hence the demand for hot water sometimes increasing the flow?

 

[Agile]

I can only take into account what you have told me as I have not examined the boiler.

The fault is associated with the water flow, flow switch actuator, pump or the main PCB ( which powers the pump! ).

Its nothing to do with the ignition PCB or the fan!

Most of these faults are associated with the pump or the water circuit.

Thats pretty much all that I can say on an internet forum without having seen the boiler myself.

Tony

 

[Redspike]

OK Tony, appreciate that. I'll have another look at those and let you know how I get on.

 

[Scrum-Master]

Hi, did you manage to resolve the issue. I am having the same issue with the M90e24s boiler.