Williams counter flow gas wall furnace pilot on/off issue

In 2005, a model 5507332 Williams counter flow gas wall furnace was installed in my cabin. Has worked fine until this weekend. Here is the issue. Set thermostats for heat, select higher than room temperate, pilot lights for about 2 seconds or less, pilot is extinguished, cycles, lights again for 2 seconds or less, and continues like this. Sometimes, you can hear the Pizo-electrical trying to light, but pilot doesn't light and eventually stops and cycles again.

I assume it is likely either the gas valve or the Honeywell controller. The controller is easier to replace than the value, do to space limitations. Also, I did eliminate the thermostat and wired direct to make sure it wasn't that.

What do you guys think?

 

The pilot heats a flame rod which proves a flame exists. If it is dirty signal is compromised. Clean the rod by wiping with a dollar bill or scotch type pad. See if that helps as a first and hopefully final step. Or the pilot may be in need of cleaning..

 

Ok, I'll try that. So you think it is the thermocouple, I think that's what they call them, not sending a signal to the controller to keep the pilot gas valve open? Would that explain what it keeps cycling?