Glowworm 50ff Ignition Lockout

[nick9one1]

I have a Glowworm 50ff that fails to light sometimes. Maybe once a week the Reset LED is solid and Burner LED is flashing fast.
Most of the time it sounds like it attempts to light itself two or three times

a successful light usually sounds like this

fan on..
click click click
woosh

then a pause,

fan on..
click click click
woosh

(reset light out, burner light green)

When it fails the failure mode is ignition lockout (according to manual). I believe I have a new PCB (green LEDs).
Is it most likely a new electrode that needs fitting? Or maybe the thermistor isn't detecting the lit pilot, hence multiple attempts to light?

I'm not a gas registered so have no intention to fix myself, just trying to get an idea of cost.
Its a 20yr old boiler so weighing up repair or replacement

Thanks!

 

[terryplumb]

Could be a number of things ,but after 20 years service it's probably time to budget for a replacement .

 

[nick9one1]

Just needed a service.

This was the second round of cleaning the heat exchanger.

We bought the house a year ago, so no idea when it was last serviced.