Suprima 60 lockout & ignition problem

[chris m]

I had a new PCB fitted in Sept. after 9 months of intermittent lockout problems.
Yesterday it locked out again and when I reset it there is a flame which stays on for a few seconds.It doesn't seem to want to stay alight.
If I can get it to light, it is then locking out within 20 minutes.
If the PCB is faulty that's under guaratee, but could it be something else?
Any suggestions?

 

[AnonymousImport]

Flame sensing electrose, HT lead from it.

Gasman

 

[chris m]

Thanks. That's interesting. I had the engineer who fitted the pcb look at it. He got it working, said it was grit in the pilot. Less than a week later it has gone done again.
Been out to buy fan heaters until I can get him back.
He reckoned everything is governed by the pcb is the flame sensing electrode a separate part?

 

[DP]

I did not know Suprima had a pilot!!!

 

[MANDATE]

As I understand it there is no permanent pilot light as such, there is electronic ignition so you can have the wrong size gap or it could short to earth due to faulty insulation therefore producing the spark at the wrong place. ( a new ignition lead is about £2.00) The spark is generated by the pcb.
The gas valve does have 2 solenoids and I examined the innards of one a year ago and came to the conclusion that flashing up the boiler might be in two stages ( I'm not sure) it makes sense if it is difficult or impossible to ignite the full flow of gas. If this is true then stage one might be called a pilot light.

 

[chris m]

So you don't think the pcb is faulty here.
This info is useful. Is the ignition lead the same as the HT lead that 'gasman' mentioned.
Please explain why if it lights initially it won't stay lit, surely that's the gas supply, and secondly, why was the problem intermittent at first........ and thirdly (I know you are all clever) Why is it that I can get it to run perhaps once in a day, for about half an hour?
Thanks

 

[MANDATE]

Sorry I can't claim to be one of clever ones!
All I know that my sons suprima give intermittent problems over a period of weeks and we examined and tested as much as we could.
The fan and air pressure switch was checked out and found OK.
The HT (high tension) lead is the ignition lead and this was changed on the advice of potterton who claimed it had been the cause of problems.
Whilst this was going on we had a situation where nothing happened and there was no smell of gas to ignite and suspected the gas valve.
A heating engineer confirmed the gas valve had bust and fitted a new one, but this did not stop the intermittent problem.
We was aware from another forum 'plumbing pages' that there were quite a few problems with the pcb. Eventually we decided to change the pcb and found potterton had just introduced a later version with a different part No.
It cost £134 but we could have had the old pcb reconditioned about £48.
However we fitted the pcb and no further problems.

I've dismantled the old gas valve and I noted that when the main gas valve is closed there is still a path for gas to the burner, I assume this may be the initial stage for the pilot light to light prior to the main valve opening.
I recall there was two solinoids, one I tested and found OK the other had gone bust and there was a small hole in the plastic casing which I enlarged until I found the actual break in the coil.
I also examined the old pcb with a magnifyier and found quite a few soldered joints had cracked, these were on the bottom of the terminal posts.
These cracks explain why sometimes it works and sometimes it don't.
Other readers with similar problems have re-soldered the joints with sucess.
I also consider that the heat generated when the boiler does work plays a part in this, making the cracks open more.
Sometimes a faulty coil on a car would operate only while it was cold.
I still feel the pcb could be the culprit, was it the newer version or one he had in stock, check the fan/air pressure switch first.
You can check this out on www.curzoncare.co.uk, they show the latest version.

 

[chris m]

Many thanks to Gasman and Mandate for your advice about the electrode lead.
I hope I haven't spoken too soon, but I ventured into the boiler and discovered it sparking where some of the lead was exposed. I removed the lead and I managed to drag the insulation back into place.
It's been working ever since!
I have also bought a new lead (£3) for when it starts to play up again.
This is a very useful website.
Thanks again