We have a Goodman Heater, GMT Series, that recently started to sound like it is struggling to turn on. The LED blinks three times when it is struggling and the panel says that according to the blinking, we should check venter pressure switch or vent blockage. It was eventually starting and would then go solid but the sounds continued. Since then, it has basically stopped. It will try for a while and then give up. Any ideas? Thanks.

Not sure if GMT is 90 or 80 percent efficient. It can be a bad pressure switch, plugged flue pipes, obstruction in the draft inducer blower motor, water or foreign objust in the vacuum hose or ports. If it is 90%, it can be a plugged drain or trap.