[sand2005]

Hi,
Hope you can help me to look at the right direction...
Have Goodman furnace for 5 years, it's GMVM96, was running no problem all the time.
Recently it started failing to start up heat. When it happens I find the furnace with solid "H" in the diagnostic window and no flames. Usually restart would solve the problem but it started getting worse: Lately when I restart the furnace with the switch, it attempts to start, the fan is on, ignitor starts, flames are on and visible, and then fan is slowing down and eventually the flames are shutting down. Furnace makes 3 attempts and then shuts down with the E0 code. I used Fault Recall button to clear up the history and after that the furnace started as normal. This happened more than twice now so there must be definitely a problem.
What I am not getting is that if that would be a physical problem with something, the furnace would not start at all, but it is intermittent so I don't know where to start. I checked and cleaned the ignitor sensor, changed the filter and thermostat batteries, checked pipes. Please help.

 

[user_12345a]

The most likely cause based on the description is a dirty flame sensor rod producing a marginal sensing current.

Remove it and clean it with steal wool or maybe sand paper.

Make sure the connections are good.

The current is very low, in the millionths of an amp so even a very thin coating of carbon or dirt on the rod can create issues.

Code from service manual attached.

 

[sand2005]

Thank you so much for your reply, sorry, I forgot to mention - I did check and clean the flame sensor.

 

[user_12345a]

The error codes may be different for the modulating version of the furnace, looked up the two-stage.

check the schematic for error codes.

Bad ground or bad connection (to the sensor or valve) can cause the same problem.