Constant E3 from heater

The only issue from our first weekend shakedown is the living area fireplace heater giving E3 immediately upon trying to heat. I can reset it by throwing the dedicated breaker for the heater (no need to disassemble and unplug it, just throw the breaker) but after powering back up, with the error message gone, it re-appears as soon as the set point causes the heater to power the heating element.

I want to try blowing out the air intake / outake per simple things to try that I have read about on-line. Has anyone take the front panel off their heater / if so can you tell me how you did it? Before I just go ahead and remove whatever screws I can lay eyes on, I thought I’d ask.

I’ll also call Brinkley tomorrow before doing anything.