I'd have it looked at by some local boiler or hvac slack jaw. There are
plenty of reasons the boiler could have shut down....dont know exactly
how your boiler is set up but most gas equipment is equipped with
several "safeties" which will shut the thing completely down in the
event things are not running right.

Could be a thermocouple gone bad but it could also be other
things....we just dont have enough info on your particular piece of
equipment to know.

~: