I have a 20 year old Rheem Gas Furnace with a standing pilot light.
When I lite the pilot this season, everything worked fine. Furnace
Fired up and all was good. Replace the panel, and by the time I took
A few steps from the furnace it shut down. Now it will not relite. I have
Jumped the white and red wires at thermostat and nothing. Is there a
Way to check the gas valve or what else can I try??

Thank you for help

Check door safety switch if applicable.it might have opened when you replaced the panel.

Is the pilot still working?

Yes it does have a door switch, I have checked it and it is working fine... the door is on.
The pilot lite is burning, and seems to be operating corectly.

Check for 24 volts at the transformer.

I'm getting 20 volts at the transformer...

By the way, thank you for your help.

Can you walk me thrugh liteing my furnace

Is it possible for someone to walk me through on how to lite my furnace