ADP SEP145 A-5 natural gas ceiling mount commercial heater

[Tom27]

ADP SEP145 A-5 natural gas ceiling mount commercial heater
Unit has been working fine for 3 years. LED code is fast flash, indicating normal operation, Call for heat. Gas valve opens, fails to fire, shuts down,
repeats for normal 3 X. No change in LED code. Looking for next steps in diagnosing this unit. No help from ADP (Advance Distributor Products.)

 

[45yearsagasman]

This is a UK based forum and although we have that type of heater in commercial premises over here, I am not familiar with the ADP models.
I have Googled it and there are plenty of agents on your side of the pond.
My first thoughts are a lack of ignition spark.