Troubleshooting a Gas Furnace

• PROBLEM: Gas Furnace Produces No Heat

• PROBLEM: Gas Furnace Does Not Produce Enough Heat

• PROBLEM: Gas Furnace Comes On and Off Too Frequently

• PROBLEM: Gas Furnace Blower Does Not Turn Off

• PROBLEM: Gas Furnace Has Noisy Operation

• PROBLEM: Furnace Pilot is Out - Relighting a Pilot

 

 

PROBLEM: Gas Furnace Produces No Heat:

Possible Causes:

• Thermostat set too low and no calling for heat
• Thermostat not working
• Circuit breaker or fuse controlling the furnace is tripped or blown
• Natural gas or propane control valve is closed
• Pilot light is out

Possible Repairs:

• Check that thermostat is in heat mode and has appropriate temperature setting
• Try moving dial setting up or down a few degrees
• Clean contacts in thermostat if it is a non-digital type
• Reset tripped circuit breaker
• Replace blown fuse
• Relight pilot light

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PROBLEM: Gas Furnace Does Not Produce Enough Heat:

Possible Causes:

• Dirty furnace air filter
• Gas burners may be dirty or need adjustment

Possible Repairs:

• Replace dirty air filter
• Call furnace service technician to have burners adjusted.

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PROBLEM: Gas Furnace Comes On and Off Too Frequently:

Possible Causes:

• Dirty furnace air filter
• Blower motor problem
• Thermostat problem (heat anticipator)

Possible Repairs:

• Adjust thermostat heat anticipator
• See also Troubleshooting a Thermostat
• Replace dirty air filter
• Oil blower motor lubrication ports (usually at each end of shaft) with light weight oil
• Check for proper belt tension. Belt should depress about 1" at center of span.
• If too loose, tighten belt.
• Replace frayed belt.

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PROBLEM: Gas Furnace Blower Does Not Turn Off:

Possible Causes:

• Thermostat set to fan continuous
• Faulty fan limit control switch on furnace (if thermostat has no fan setting)

Possible Repairs:

• Change thermostat fan setting
• Reset or replace furnace fan limit control switch

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PROBLEM: Gas Furnace Has Noisy Operation:

Possible Causes:

• Higher pitched "squealing" sound may be caused by slipping blower belt or motor or shaft bearings in need of oiling
• Lower pitched "rumble" sound may be caused by a poorly adjusted pilot light if this problem occurs with the burners off.
• Lower pitched "rumble" sound may be caused by dirty gas burners if the problem occurs with the burners on.

Possible Repairs:

• Oil blower motor lubrication ports (usually at each end of shaft) with light weight oil
• Check for proper belt tension. Belt should depress about 1" at center of span.
• If too loose, tighten belt.
• Replace frayed belt.
• Adjust pilot light
• Call furnace service technician to have burners adjusted or cleaned.

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PROBLEM: Furnace Pilot is Out - Relighting a Pilot:

Possible Causes:

• A pilot can go out due to a strong draft, dirty orifice or dirt in the gas tube.
• The thermocouple may also be faulty and is shutting off the gas supply.

Possible Repairs:

• Re-lite pilot

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Tips and Articles:

Winter Electrical Safety Tips

Heating Help/Tips

Troubleshooting a Gas Furnace

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