gas furnace stops intermittently

Old 10-28-05, 06:37 PM
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gas furnace stops intermittently

My gas furnace is 36 yr old. After 10 yrs since I bought the house for the first time I noticed that the pilot light was out. I followed directions and lit the lamp and started the thermostats. The main flame came and after a variable period of time went off, some times taking the pilot lite away with it. At times it is with the igninition of the main furnace itself (like a mini-explotion that takes place probably creates a draft). I called a service repair man and he wasb't certain what was causing but replaced the main gas control and I see a new copper wire going towards the pilot lamp (connected to thermocouple?). The problem seem to be continuing although not so frequently but twice a day I have to light the furnace and now always he pilot is out. The pilot is a blue flame and has a thickeness of a fat pencil. Since the start of the main flame took about 5-10 seconds after the opening of the main gas valves and made a more than usual mini explosion, I have reduced the air intake to the three lighting chambers a little and now the start is much quieter and less scary and main flame remains nice and blue and fully lit in all three areas. The repair man is expected again in three days. I want to know the purpose of the copper wire-does it conduct electricity from the thermocouple or heat from the pilot (because it is cold to touch even if takes 15 seconds gas to light).what is the ideal size of a pilot light. what is the ideal way to adjust the air intake of the three do you check wheher the thermocouple is at fault? how does one clean the pilot lamp gas tube? (I'm not sure whether there is a partial obstruction

Many thanks

Old 10-28-05, 06:49 PM
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Mini explosion

The right way to adjust the air is with instruments to measure the oxygen & carbon monoxide of the exhaust gas.

The "wire" connecting the thermocouple to the gas valve is basicly exactly that, a wire. The thermocouple generates a small electric current ( aprox. 30 millivolts). This current is what keeps the pilot valve open. No flame = no current = pilot valve closed

The pilot flame should envelope the top 1/3 to 1/2 of the thermocouple.

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