Glow Worm Ultimate 50FF Intermittent Firing Problem

[Geoff.B77]

I have a problem with intermittent firing on a Ultimate 50FF boiler.
The boiler starts up ok as normal, comes up to temperature ok and starts to heat up the radiators / HW, with the burner cutting off / on as normal. After about 20 mins or so the main burner cuts out and immediately re ignites and this on/off scenario will continue every 20 seconds or so.
About two months ago, following exactly this scenario, the boiler cut out completely and although the igniter lit the pilot, there was no main gas on the burner. I found that one of the two gas valve solenoids was open circuit and replaced it. Hey presto, everything was fine, until recently when the intermittent firing phantom has returned.
I have put a voltmeter across the main gas solenoid (ie the one that I replaced in August).. When the boiler is operating normally there is 240v across the solenoid, each time it fires intermittently the 240v reduces to virtually zero, but immediately picks up back to 240 and the boiler main gas reignites. So Iguess its not the gas valve SOV, there must be some other reason why there is an intermittent loss of voltage to the SOV.
Can anyone help please, Weather is starting to turn cold up here.
Many thanks. Geoff.B

 

[Rob]

um....pcb?or is that too obvious ??

 

[Geoff.B77]

Help!! Fitted a complete new PCB and unfortunately after about 5 mins or so when the boiler gets roughly up to temperature the intermittant firing returns.
What else would cause intermittant loss of voltage from the PCB to the Gas valve. Each time the firing stops this is preceded by the fourth LED on the board going out, and then the LED comes back on prior to the boiler re igniting. This then goes off & on every 10 seconds or so.

Hope someone can advise on this irritating problem.

Thanks
Geoff.

 

[gas4you]

Fan venturi blocked, aps tubes, aps its self faulty?

 

[ollski]

pilot solenoid dropping out?

 

[Geoff.B77]

Fan venturi blocked, aps tubes, aps its self faulty?

Dave,
checked out the APS and 240v is always present on the correct c/o contact when the boiler is firing normal. When the intermittant firing starts there is no difference. I.E I am assuming that if the APS was dicky, you would lose the 240v to the n/o terminal.
Everything else seems to be normal except for the 4th neon going off in tune with loss of volts to the main gas SOV. All other 3 remain lit.
This is a brand new PCB fitted tonight so it would be most strange if it was another PCB fault. There must be another reason but God know what!!
Any other ideas.
Thanks. Geoff.

 

[Geoff.B77]

pilot solenoid dropping out?

Hi ollski.
The 240 volts are ok to the pilot SOV coil. (ie the voltage is not on / off the way the volts to the main SOV is) .. If it was the pilot sov coil itself that was dicky, and it was dropping out whilst the main gas burner was firing, would that still intermittantly have an effect on the main burner sov coil supply from the PCB?? I'll try unplugging the pilot SOV terminal whilst its firing normal and see if it has the same effect.

Thanks. Geoff.

 

[ollski]

Yes because there would be no flame rectification so the supply to the main gas valve solenoid would be cut by the pcb.

 

[Geoff.B77]

Yes because there would be no flame rectification so the supply to the main gas valve solenoid would be cut by the pcb.

I think that may be the answer. I unplugged the pilot Sov terminal whilst the boiler was firing normally and the fouth neon went out, the main gas valve closed and the boiler ignition system continued to try and light the burner. So I'll replace the pilot SOV coil next week and see what happens. Certainly a funny one!! Thanks. I'll let you know. Geoff.

 

[Jerryg777]

Geoff

My 50ff has developed the exact same problem. An engineer has already replaced the PCB to no avail and is now stumped about what is causing it. Did your last attempt to fix (replacing the pilot SOV coil) work? I would love to find an answer and get this sorted as it is getting really cold now!

 

[Geoff.B77]

Jerry,
The problem appeared to be that the pilot flame confirmation back to the PCB (via the HT lead) was poor or intermittant. This causes the PCB to think that the pilot has gone out and interrupts the 240v to both the Pilot SOV and the Main SOV, hence the burner goes out momentarily and then the sequence starts again, reignites the pilot and then the main burner. (Three neons should stay lit on the PCB and the fourth would go out with this condition)
I also thought I had an intermittant fault on the pilot sov coil. (The main burner sov coil failed in August and the coils are identical)
So I did two things, I stripped the pilot burner and igniter sparking terminal down and cleaned everything up and also made sure that the wire to the sparking terminal was clear and not jammed anywhere. Make sure that the igniter terminal gets a strong flame on it when lit.
Because I also suspected the pilot SOV coil I replaced it (its an easy five minute job to replace )and touch wood, its been fine since.
So it could be either a faulty pilot SOV coil or poor feedback to the PCB. Either one would cause the same result.
Be interested to know how you get on.
Regards Geoff.

Geoff

My 50ff has developed the exact same problem. An engineer has already replaced the PCB to no avail and is now stumped about what is causing it. Did your last attempt to fix (replacing the pilot SOV coil) work? I would love to find an answer and get this sorted as it is getting really cold now!

 

[Jerryg777]

Geoff

Thanks for the quick response - will give this a go tonight and let you know what happens!

Jerry

 

[Jerryg777]

Geoff

Success! Engineer turned up last night and read what you had done. He was convinced that it wasn't the pilot SOV coil but stripped the pilot burner and sparking terminal down, gave it a really good clean and repositioned the spark electrode and lead. Hey presto, everything appears to be working now - warm house, happy wife and kids! I suppose I should wait until we get through winter problem free before I totally relax about it.

Thanks for posting your questions and thoughts on this site, it has certainly helped me avoid some unnecessary expense. If you are ever in Dorset, let me know and I will buy you a pint!

Regards

Jerry

 

[markyk]

Hi Geoff
im having a problem with a ultimate 50 ff, one of the resistors on the control board is burnt and i cant make out what size it was, its resistor "R11" which is located beside the fuse, if your looking at the board with the bottom fuse in the bottom left hand corner! im going to ask a big favour of you would there be any chance you could have a look at your control board and tell me what colour bands are on this resistor, ive contacted glowworm but they wont release this info due to the manufacturer of this board, any help on this would be really appreciate
Thanks, Mark