Biasi M90E.24S takes a few goes to stay lit when cold!

[hurders]

I have an M90E.24S which seems to have developed an odd issue. I only use the boiler every few days as it's in a house I'm renovating so I'm not there all the time.

When I do come to use it, it's generally been switched off for a couple of days since the previous visit. I switch it on for C.H. and it fires up seemingly without issue but then it'll cut the flame out after a few seconds, the fan and pump sound like they continue to run, then after a few more seconds it fires up again only for it to cut the flame out again after another few seconds. This cycle, flame on -> flame off -> flame on etc. goes on for several cycles until eventually it seems happy and the flame stays lit and all is seemingly well.

It only has this odd issue the first time it's been stood unused for a couple of days. Once it's got itself going, it doesn't seem to have an issue and it'll happily function properly for both the C.H. & D.H.W. turning on and off when requested. Even if the C.H. is turned off for a few hours it'll come back on just fine when requested again. It's only when it's been off and I come back a day or two later that it'll have to go through the flame on/off cycle on initial request for CH. If I request D.H.W. first after it's been stood a couple of days it does the same thing, flame on/off cycle a few times before finally settling (warming up?) and allowing the flame to stay lit. So the fact the C.H. and D.H.W. both cause the issue suggest to me that it shouldn't be a heat exchanger issue?

I've been using the boiler sporadically over the last year while I've been working on my house and it's worked fine over the course and this issue seems to have started in conjunction with the colder weather so I'm wondering (guessing!) if when it's left a few days in a fairly cold house something seizes up/sticks and it takes a little while/heat to free up?

When this problem occurs it never locks out and seems quite happy to re-ignite and try again and again and again etc. until the flame does stay lit and, as said, once it finally stays lit I don't have any issue with CH or DHW until I come back a day or two later.

Any ideas?

 

[hurders]

Well, still haven't got this issue sorted but I'm trying to diagnose and I'm tending to think it could be the modulating gas valve causing the problem.

Turned it on for CH yesterday after it had been off for 3 days and, as before, it fired up, then a few seconds later went off (pump & fan still running), then a few seconds later fired on, off, on, off etc. Eventually after probably at least 10 cycles of flame on, off, on, off it finally stayed lit and all was (apparantly) ok and it worked as normal for the rest of the day.

When it's firing on, off, on, off etc. seems to be a fast, fairly quiet, clicking noise coming from the area of the modulating gas valve (FYI it's definitely not the primary flow switch as thats popping out as it should and operating the switch). The clicking continues until the flame extinguishes, then the clicking begins again when the flame reignites a few seconds later. I noticed that when the flame does finally stay lit the clicking stops. I also notice you can usually tell it's going to stay lit because an odd noise (quite a loud electrical buzz/vibration sound) occurs then fades away. Could it be something to do with the on-off operator coils? and if so why would it work ok once it's done it's on, off, on, off routine the first time?

I know I more than likely going to have to get a gas safe man in to have a look and fix but I'm trying to do a bit of a diagnosis so I have some idea what the problem is first.

 

[hurders]

Anybody have any ideas?

I'm now wondering if it could be a PCB fault?

 

[Agile]

It might be an ignition PCB fault if it has two PCBs. On this boiler you could change that yourselgf but as they are exp[ensive its better to have the problem correctly diagnosed rather than throwing parts at it.

But as its a conbustion related issue we can only advise you to get a competent gas registered boiler engineer.

Tony

 

[ianmcd]

Do you have a gas hob or cooker in the house? if yes try them before you try to light the boiler it is possible that the meter regulator is sticking

 

[Agile]

As the flame is coming on its seems unlikely to me that the governor is sticking in this case.

Anyway, regardless it needs an RGI to properly diagnose the faults.

Tony

 

[hurders]

Well it doesn't seem to be a sticky gas meter governor. I fired up all the rings on the gas hob and they lit no problem and at full flame.

Had a look at the ignition PCB last night. I think the (fairly loud) electrical buzz noise that I mentioned previously is coming from a relay? on the ignition PCB, the one which the wires from the ignition electrodes connect to. Taking the wires off the terminals at the relay end I noticed there was a lot of corrosion/rust built up on the terminal connectors so I cleaned that up and tried it again but no joy, exactly the same, flame lights, then off, then on, off etc. and then finally stays on after several attempts.

Looks like it could well be an ignition PCB fault but I'm going to get an RGI in to diagnose.

 

[Agile]

The ignition wires connect to a transformer, not a relay!

Tony

 

[hurders]

Ah, guess my electronic skills aren't too hot!

Perhaps the electrical buzzing noises are coming from a different nearby component on the board, they do definitely sound to be coming from the ignition pcb though.

Couldn't see too much wrong with the solder joints underneath the board but did notice one of the capacitors looked a bit swollen with a little white crust around it and felt a little loose.

I'm half inclined to risk buying a new board just they aren't particularly cheap as you've already pointed out.

 

[Agile]

Regardless it needs an competent RGI to properly diagnose the faults.

 

[hurders]

Ok got RGI coming tomorrow to have a look.

I noticed last night that it's continuing to spark once the flame has lit which I presume is causing the flame to then shut off a few seconds later (not sensing the flame correctly). After the usual 10 or so cycles of on/off, on/off etc, the flame lit, sparks stopped and flame stayed on accompanied by the electrical buzz (I think from a PCB relay) which quickly faded away and the boiler worked fine for the rest of the night.

Could it be the flame sensing electrode, or is PCB fault more likely? (the buzzing noise makes me think this is more likely).

Obviously the RGI will diagnose, I just like to have some idea beforehand what his potential diagnosis is going to be/what he should be looking for.

 

[Agile]

Only the RGI at the boiler can determine what the problem is.

In any case we cannot give you advice on gas relater matters which you would use to try to try to repair the boiler yourself.

Tony