The heater is in lock-out. It is failing to detect or sustain a flame. Current signal at FLAME terminal is less than .6 microamps. The correct flame signal should be between .6-1.0 microamps.
Have you cleaned it according to the manual as well as checking spark gap (0.110-0.140) ? If you have a DVM and can make some basic voltage checks short of that and depending on your warranty, they might send you another board. I know they have had some problems with boards in the past.
Just for piece of mind I would also confirm that the heater is meeting all other requirements like gas pressure, thermostat operation (is it calling for heat?), obstructed flue etc..
You can call them for help at 800-251-0001 or visit
www.mrheater.com. Have model#, date of purchase and description of problem.
