What does "low voltage input" mean on my boiler?

My boiler(Burnham series 2 natural gas model #P-205-WI)has turned on twice already this year, now nothing. I opened it up and the flashing diagnostic LED says " low voltage input, if error corrects, normal operation resumes after 1 minute". I have checked the fuses and they are fine. I assume it is getting power as the LED is working. Could it be the thermostat? Is this something I could possibly fix, or should I call a repairman? Thank you in advance for the advice.