I have a bryant model 395A furnace that was installed in 1986. The pilot briefly lights and then goes out. There is a 646A-X gas valve for the heater. When I turn the thermostat on I get a solid 24 VAC Between terminals 4 and 3 with intermittant pulses of 24 VAC between terminals 5 and 3. The pilot turns on briefly every time there is a pulse between terminals 5 and 3 and then fades out. Is this a problem with the valve?