Pilot on with no clicking noise-bad thermocouple?

[kepano77]

Hi, Have a really old (> 30 yrs.) furnace that may have a bad thermocoupler? Despite the thermostat set to turn on the heater, the pilot light is on-appearing to have badly burned the thermocoupler(?) unit. There is no clicking noise or fan followed by heat. Does this 'sound' like a thermocoupler issue?

there is no visable manufacturer less Pacific Industries Inc. SF. CA, with a model# of A80BD

Any assistance will be greatly appreciated. Thanks!

[HayZee518]

the first givaway that the thermocouple is bad is that the pilot flame will not stay lit. the thermocouple produces a millivolt voltage that pulls in and holds a magnetic valve open. when you light a pilot and you are required to "hold in" a button for a minute, you are manually opening the pilot valve which is then lit, the flame of which heats the thermocouple to produce the voltage to keep the valve open when you release the button.

[kepano77]

then the thermocouple is not the problem as the pilot is on but burning the thermocouple tip to the point that it no longer looks like a tip.

any ideas as to what could be wrong? thanks!

[HayZee518]

Is there a second thermocouple in the flame? If there is then you have a thermopile gas valve. A thermopile unit also generates a millivolt signal but this one operates the burner solenoid to open the main gas valve. A thermopile unit uses its own thermopile thermostat. a standard honeywell thermostat will not work with this type of furnace. to try it remove the thermostat and just touch the two wires together and listen for the click [ the solenoid valve opening]