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Morning all
I’ve got a 15 year old oil boiler and I’m having intermittent fails to start.
It’s a Worcester green star oil fired boiler. Sartori control module and photocell, bentone st108 burner. Danfoss fuel pump, solenoid and spark generator/transformer.
Basically it’s fine most of the time but 3 times now has failed to ignite in the afternoon/evening.
It’s getting a run signal, starts the burner fan, good airflow and transformer sits firing away but won’t ignite.
I had an engineer out a month ago (after the oil company forgot to put the cap on the oil tank) and he drained the water from the tank, cleaned the fuel lines and tiger loop, still wouldn’t start so he replaced the fuel pump and coil and it was fine - for a month.
Last weekend it failed to fire again at the 16:30 timed start up. I know a boiler guy who was unavailable but gave me a bunch of parts. He said it could be a zone control valve issue (due to hot water only sending run signal when heating zone valve turned on) so I replaced the zone valves but no change. By replacing it I learned how it works so tested the micro switch which was fine, and the servo runs fine. Fully engaging when in run position. Stats all good.
I replaced the burner control module and no change. I put a new coil on the fuel pump, no change. I left it off overnight and it fired up in the morning no issue.
1 week later I have the same issue so grabbed some more parts last night. Replaced the photocell, no change. Replaced the spark generator as there was what looked like a hairline crack, no change. Spark tested at the generator and arcing to an insulated screwdriver nicely (though not a big spark). Left off (at the fused spur) overnight and tried to restart it this morning. Didn’t fire initially but held the control module reset for 5 seconds and hey presto, ignition.
My thoughts are as follows:
The spark generator is firing the whole time so I have a run signal - it’s not a thermostat/controls issue.
I have a reasonable spark from the spark generator and the same with the new one. Not spark gen. spark tested by removing HT leads so not checked inside the burner, checked at the generator end only.
It’s had 2 new coils so not a coil.
New fuel pump last month.
Water removed from fuel lines. Crap drained from tank.
Fire safety valve operating and reset cycled.
So - I’ve got fuel,I’ve got spark, I must have good chamber pressure as it’s running again now and in between failures. I wonder if the electrodes are covered in crap and when it’s cold the pressure is too low to fire the electrodes enough to ignite? When it’s warm pressure is good so a crappy spark is enough but when it’s cold pressure drops and the crappy spark isn’t enough? I’ll get a guy out as I’m not gas safe so won’t remove the burner to check the electrodes myself. Ideas welcome though as I want to point the guy to the right place and reduce labour costs if poss.
Cheers guys.
Recently had trouble with mine failing to start. Finally traced it to an isolation valve in the fuel line. The valve stem seal had failed allowing air to be drawn into the fuel line so sometimes it would fire, sometimes it wouldn’t
Seems to be quite a common fault now that I know what it was
Two pipe oil line? Could be air being drawn in on the return. Has the nozzle been changed too?
Another vote for nozzle here, it has it's own separate integrated filter - which may be blocked or frozen with water dependant if it is an internal/external boiler.
Is this a 'Heatslave' 18/20 or similar where the fan, igniter and pump are held into the main chamber with 3 hex head bolts?
We just scrapped ours and I still have most of the parts here. I don't want to cloud your mind, but despite fixing ours successfully many times over the years I gave up with a no start fault and called a boiler man in. Did his head in as well, but because it is such a common boiler he just played swaps with the spares on his van. Fault turned out to be the capacitor for the motor.
Not sure if I'm helping . . .😊
PM if you think any of the bits I have are any use to you