Empire LP direct-vent start-up problem

[goggomobil]

Hello.

I have an Empire 35,000 BTU wall furnace (direct-vented) which is almost eight years old. It has a Robertshaw millivolt gas valve system, with a standing pilot. It is in use from October through early April, in a moderately cold climate. Everything is original, and it has never been serviced.

Two days ago, I noticed the room temperature was low, so I moved the thermostat to listen for the burner to ignite. I heard nothing, so I repeated this and still nothing. I removed the front panel and observed that the pilot was operating properly. The thermocoupler seems to have a small amount of burnt deposits on it. I checked the wiring (particularly, the terminals) and everything appears to be ok.

I decided to tap the gas valve and it ignited immediately. All other operating aspects of the heater seem to be normal. My question is: Does the condition of the thermocoupler affect this, or is it more likely that the gas valve needs replacement?

Thank you for your time,

Jack

P.S.: The LP storage tank is at 75% capacity. Also, I seem to remember that when lighting the pilot this season, the 'OFF-PILOT-ON' knob on the gas valve seemed reluctant to return to its normally outward position (from being pressed inward on the 'PILOT' position).