Suprima failure to ignite.

[Richard Savage]

Seasons greetings

My Suprima 100 has died - or is trying to die.

Greeted on return home by the flashing red LED indicating lockout or similar failure.

Pressing the reset button resulted in three attempts to ignite the gas with plenty of fan noise, sparking at the spark gap but no ignition of gas.

So, I removed the covers and front insulation cover (the bit that gives access to the burner jets). Had a look around for dust and other foreign bodies. All is clean and tidy.

Ran through the fault finding list in the handbook except for the bit that requires measuring the voltage across the gas valve. Still would not light after three attempts. B*******s, it's the gas valve. Tried to light it a couple more times prior to finding meter to check supply to gas valve and then it did light but with a very jerky flame - remember the front cover to the burner is off so maybe there is the wrong amount of air.

Joy! Switched off.

Put the insulating cover back on and turned it all on again. Back to three failed attempts followed by lockout.

Removed insulating cover and tried again. It lit with a proper flame. Gingerly refitted the insulating cover keeping fingers well clear of blower motor fan (previous bad experience). Boiler continued to run. Refitted main covers.

No, I haven't dared resetting it in case it dies.

Can anyone suggest a fruitful line of research or thinking as to what may be wrong?

TIA

Richard

[Phil L]

Air in the gas pipes?.....the jerky flame may suggest this, FWIW I ran my last boiler for six months with the front cover off because I had to remove it every time the gas went to relight the pilot (prepayment meter), and it didn't burn with a jerky kind of flame.

[Ed Sirett]

@Phil L: This boiler does not have a permanent pilot light in fact it probably has almost nothing other than it burns gas in common with the model you had trouble with.

OK. This boiler is not designed to operate with the cover off. The jerkiness will stop if the cover is in place.

You can diagnose a failed gas valve by seeing that when a voltage (usually

230V ac) is applied to the valve there is no corresponding gas pressure in the outlet from the gas valve. (Zero governors [1] need different tests). The gas valve is unlikely IME to be the culprit and also to be intermittent in failure (unless the electrical connection). If you get something you can put the GV to the end of the list of possibilities.

Most likely there is an ignition or flame detection problem. As it's a Suprima the standard tactic is to replace the boardand the ignition lead and see if things improve. On all other boilers you would start with the ignition electrodes and/or the ignition lead.

[1] Such as you often find in condesing boilers.

[geoff]

The suprima has a DC voltage applied to the gas valve

The manual is wrong on the voltage

If the pcb is delivering 320v DC (as indicated in the manual) to the gas valve solenoid, prolly the solenoid is knackered - check the resistance, should be 4200 ohms

If the pcb is delivering about 210v DC, then the pcb is delivering the correct voltage into a working solenoid - another problem with the gas valve

If the pcb is not delivering the above voltages to the solenoid, then you prolly have a fuqt pcb

If you have a red HT lead, then change that - part number 407753 the red HT lead fails to flame sense properly and should be changed anyway

If you have any questions or need a pcb or HT lead, you have a 3 hour window between 9 am and midday tomorrow where I can lead you through homing in on the problem

01923 229224

[tony sayer]

In article , Richard Savage scribeth thus

If all else fails get a soldering iron and go over all the joints on the PCB unit these are very good at developing intermittent dry joints...

and if no go cetled for a replacement board;!..

[Richard Savage]

Replaced the PCB via CET to cure the frequent lock out problem (which it did) after waving a soldering iron across everything failed. That was 3 years ago so it might be feeling in need of a change. If it needs replacing after 3 years I consider the money spent at CET very good value - as was the telephone help I received from them when confirming that I did need the PCB. No relation etc - just a satisfied customer.

Richard

[cynic]

The open cover probably allows more airflow through the fan/flue system and MAY be indicative of an airflow sensing problem. Try removing the sensing tubes from the airlow sensor and blowing them clear. Also check the fan blades are clean and the air/flue route is similarly clear and clean. One of the Pottertons used an odd thermal airflow sensor but others I believe have a simple differential pressure switch. I can't recall if the sparking starts before or after the airflow is proved but the fact the flame ignites with the cover off suggests the above.

[geoff]

In message , cynic writes

Lynx 1

The Suprima has a 2 wire standard APS

Until the APS transfers, there is no spark or power to the gas valve

Happy Xmas John