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Troubleshoot the gas valve for the higher efficiency furnace
Until the early 1980s, most furnaces were pilot types. The 1980s were a time of change for furnace design. Electric pilots that left the pilot on only when there was a call for heat were beginning to be used. This eliminated the gas usage of the pilot when the furnace was off. By the 1990s, the pilot was mostly eliminated altogether. The higher efficiency furnace (one that was made after around 1990 and later) uses a different type of gas valve than the older pilot type. The gas valve opens for a short time in a trial for ignition. If the flame is proven while the valve is open, it stays open. This makes testing of the gas valve a little different. The 2 videos below cover how to test the gas valve.
These videos are used for both 80% efficient and 90+ efficient furnaces.
The simple check covers an easy way to find out if power is passing thru the gas valve.
These videos are used for both 80% efficient and 90+ efficient furnaces.
The simple check covers an easy way to find out if power is passing thru the gas valve.
This video covers using the voltmeter to check if voltage is available to the gas valve. If the "simple check of the gas valve" shows no power passing thru the valve, you then need to find out if power is available to the valve. This is when you will need to follow the second video. If power is available, (note that if the gas valve is powered by 24 volts and the voltage read is much lower, such as 14 volts, it is a ghost voltage and is a feed back from the control board).