Hello
I have a old GMP125-4. That what's going on : Thermostat in my room sending signal to furnace.Motor starting work and then is nothing... I can see trouble code (flashing light) it is 3 flashes and long pause, again 3 flashes and pause... Do somebody know what that code is mean ? - I have instruction manual but there is nothing about trouble code. PLEASE - I'M REALLY COLD!! :(
I will really appreciate for any kind of help.:)

Try cleaning the flame sensor with steel wool. That is about as much as a untrained person can do. If thast does not work call for service.