Strange failure to fire mode on Weil-McLain EG40

rexster

Starting 2 days ago, my WC EG-4.5 stopped starting in the middle of the night. Tried to restart several times, turning the power off first and then attempting to restart. The next morning (having left the power off for the rest of the preceding night), the boiler fired right up and ran all day, firing up numerous times. Then, around 4:30pm last night, the boiler would not start again and failed to fire multiple times, my last attempt was 1:30am last night. This morning, the boiler started right up again and is running now. The boiler is vented using a Kjernland power vent with an UC-1 controller and uses a Taco SR-501 relay gizmo. Boiler was serviced a few months ago and is about 8 years old. When it fails to start, the pilot comes on but the power vent never starts and the burners don't ignite.