Make: RHEEM
Model: RGDO 06NC ER
Installed: 1990
Problem: Observe glow in burner area from ignitor but the gas won't turn on. After a few seconds the glow will turn off. The Hot Surface Ignition Module was replaced in 1997. Please advise.

Some of those3 older Rheems have a pressure switch or limit device inline with the gas valve. You will need to track the 24 Volt hot leg wire from the board to the gas valve checking voltage at every device to find out which one is open. If you have 24 V at the gas valve shortly after the igniter begins to glow, you will have to replace the valve. Just a note, after the ignitor glows there will be a small click from the circuit board, it will only send voltage for a few seconds before it realizes there is no flame and stops the voltage.

NorthernHeat: Thanks for the troubleshooting tips. Am leaving for vacation in the morning. I will do as you suggest upon my return.