Well, it took a while, but it seems that there were two faults.
1: the solenoid was renewed as it didn't always open properly to allow fuel into the boiler.
2: With a new solenoid fitted, the burner did not fire when slotted home in the furnace, but did fire when out of the boiler but with the nozzle pointing into the furnace. Then, on one of the occasions when it was fully home, the reflection of sparking from the electrodes could be seen on the motor body. Further investigation showed that the electrode HT leads pass through holes in a rubber grommet which slots into the casing, and when the leads were pulled back it could be seen that the insulation of one of them had broken down. This had caused arcing from the lead to the burner casing when the burner was fully home, but the spark was OK when the burner wasn't fully home.
The attached photos show the leads in there normal position in the grommet, and with the lead pulled out showing the fault.
The grommet is very brittle and slightly burnt where the arcing has been taking place.
The rubber grommet doesn't appear to be shown in the supplier's parts book, so it couldn't be renewed at this time, but the existing holes in the grommet were drilled out enough to take the replacement leads and the grommet had to be reused.
If anyone can think of a supplier where I could get a replacement grommet I would very much appreciate knowing about it, as although the boiler is now working, I wonder for how long, as the old brittle grommet isn't the best insulator, though some insulation tape was stuck across it in way of where it touches the casing.
1: the solenoid was renewed as it didn't always open properly to allow fuel into the boiler.
2: With a new solenoid fitted, the burner did not fire when slotted home in the furnace, but did fire when out of the boiler but with the nozzle pointing into the furnace. Then, on one of the occasions when it was fully home, the reflection of sparking from the electrodes could be seen on the motor body. Further investigation showed that the electrode HT leads pass through holes in a rubber grommet which slots into the casing, and when the leads were pulled back it could be seen that the insulation of one of them had broken down. This had caused arcing from the lead to the burner casing when the burner was fully home, but the spark was OK when the burner wasn't fully home.
The attached photos show the leads in there normal position in the grommet, and with the lead pulled out showing the fault.
The grommet is very brittle and slightly burnt where the arcing has been taking place.
The rubber grommet doesn't appear to be shown in the supplier's parts book, so it couldn't be renewed at this time, but the existing holes in the grommet were drilled out enough to take the replacement leads and the grommet had to be reused.
If anyone can think of a supplier where I could get a replacement grommet I would very much appreciate knowing about it, as although the boiler is now working, I wonder for how long, as the old brittle grommet isn't the best insulator, though some insulation tape was stuck across it in way of where it touches the casing.
