Rheem Imperial 90 Plus not igniting.

Symptoms – When heat called for: tries to fire. Over and over a click from a module on the control board (ST788C1002). A green flash comes from the module on the control board that is clicking.

Ignition Control Module – Honeywell 47-22481-01 – does not give any LED indications at all - No blinks at all on the LED on the Ignition Control module.

Blower working fine.

Sensor has been cleaned with sandpaper. Ignitor appears to be fine. It was replaced about 3 years ago. Heat Exchanger replaced about 10 years ago – warranty. Burners replaced about 5 years ago. I have photos taken today ready to forward if they will help.

Sounds like to me you have a bad hot surface ignitor. If its not glowing and you can see a white ash spot on the ignitor its bad.

It's not the ignitor - I just replaced it with a new one, and same thing as described in original question.

Any more ideas please?