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Troubleshooting Guides

Click one of the links below to skip to the troubleshoot tips for that topic.

Central Air Conditioning
Electric Furnaces
Electronic Air Cleaners

Gas Furnaces
Geothermal Furnaces
Heat Pumps

Hydro-Air Systems
Oil Furnaces
Wood Furnaces

Central Air Conditioning

Basic troubleshooting for split systems:

First make sure that the thermostat is set lower than the actual room temperature. The selector switch must be on "cool." If the thermostat is programmable, be certain it has fresh batteries.
Check for power by moving the fan switch from "auto" to "on." If the blower runs, there is power. If nothing happens, a control is burned out or power is disconnected. If the system uses a furnace for heat, check that the emergency switch is on. If you are familiar with the fuse or circuit breaker panel, check for blown fuses or tripped breakers. Correct the problem one time only. If it repeats, call for service.
With the selector switch on cool and the fan switch on auto, move the thermostat well below room temp. If the blower runs but the condenser (outdoor unit) does not, check the circuit breaker panel. If the breaker is on, examine the condenser. Some have a high pressure cut out. It is a button sticking out of the cabinet, usually near the refrigerant lines. Push it in as far as it will go to reset it.
If both units are running and no cooling is taking place, touch the larger of the two copper lines exiting the condenser. If it is warm, the system is out of freon or the compressor is down. If the line is frozen or iced over, there is an air flow problem inside, such as clogged filter or too many registers closed or an object covering the return duct. A low freon charge will also cause a freeze-up. Shut the system down and let it thaw out completely. If it freezes up again, call for service.
If the unit is in the basement and has a condensate pump, the control wire for the condenser might be wired through a safety switch on the pump. Check to see if the pump is plugged in and operable.
If the unit is in the attic, there could be a float switch in the air handler or in the safety pan that will shut the condenser off if the drain is clogged. Water around the unit is evidence of trouble. Call for service.

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Electric Furnaces

Basic troubleshooting:

The thermostat must be set higher than the actual room temperature. If the thermostat is programmable, be certain it has fresh batteries.
If there is central air, or the system is zoned, make sure the selector switch is on heat.
If you are familiar with the fuse or circuit breaker panel, check for blown fuses or tripped breakers. Correct the problem once. If it repeats, call a serviceman.
Do not attempt to service the controls inside the cabinet. Deadly high voltage conditions exist.

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Electronic Air Cleaners

Troubleshooting falls into two categories: grid failure or power failure. Excess dirt or a large object stuck in the grids will cause an electrical short. A loud snapping noise will sometimes indicate this problem. If cleaning does not stop the snapping and the grids are bone dry, inspect the fine wires stretched across the terminals. If they are white from oxidation, gently run an old soft toothbrush up and down them once, then rinse and dry again.
Most electronic air cleaners have a light to show operating power. If the light is not on when the system is running and the switch is on, there are three possibilities: the power pack has burned out, the power to it has been disconnected, or the unit has a pressure switch to sense air flow and charge the grids and it has failed. Either repair means opening up the power pack, exposing dangerously high voltage. This task should be left to a qualified technician.

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Gas Furnaces

Basic troubleshooting:

Check that the thermostat is set higher than the actual room temperature. If you have a programmable thermostat, make sure it has fresh batteries.
If equipped with central air, or the system is zoned, make sure the selector switch is on heat.
Check the emergency switch ( usually a red switch plate at the top of the cellar stairs or on the side of the furnace) to see that it is on.
If you are familiar with the fuse or circuit breaker panel, see if the fuse is burned or the breaker tripped. Correct the problem once. If it repeats, call a serviceman.
On standing pilot furnaces, the burner will not light if the pilot has gone out. If you are not familiar with the function of the gas valve or lighting the pilot, call for service.
Furnaces with electronic ignition have a sequence of safety steps the burner takes to light. Information is usually attached to the inside of the burner or blower access door. Follow the procedure according to the manufacturer's guidelines to avoid the risk of fire or explosion.
Do not disconnect any piping to check for gas supply. An instrument is used to check for pressure, and checking it should be done by a qualified serviceman.
If the furnace is vented through PVC (white plastic pipe) out the side of the building, examine the ends of the pipe or pipes outside. Blockage of any kind will cause a shutdown.

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Geothermal Furnaces

Basic troubleshooting:

Be certain that the thermostat is set higher than the actual room temperature and the selector switch is set to heat if in heating mode, or that the thermostat is set lower than room temperature and the selector switch is on cool if air conditioning is desired. If the thermostat is programmable, make sure it has fresh batteries.
An easy test for power is to move the fan switch from "auto" to "on." If the blower runs there is power to the unit. If you are familiar with the fuse panel or circuit breaker panel, check for blown fuses or tripped breakers. Correct the problem once. If it repeats, call for service.
Check the water supply if fed from a well. A clogged filter or strainer may trip safety switches that will not allow the unit to run without water.
Because the controls are mounted internally and high voltage connections are exposed if the cabinet is opened, only a qualified technician should access them.

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Heat Pumps

Basic troubleshooting:

Make certain that the thermostat is set higher than the actual room temperature and the selector switch is on heat if heat is needed, or that the thermostat is set lower than the actual room temp and the switch is on cool if air conditioning is desired. If the thermostat is programmable, be certain the batteries are fresh.
Test for power to the air handler by moving the fan switch from "auto" to "on." If the blower runs, the air handler is functional. If nothing happens, check the circuit breakers on the air handler cabinet and the breakers or fuses in the main panel. If any breakers are tripped, reset them once. If they trip again do not reset them. Deadly high voltage conditions exist inside the air handler cabinet and inside the access panel of the condenser. Let a qualified serviceman open them.
If the air handler runs constantly but cannot satisfy the thermostat setting, it is possible the backup heat is running but the condenser is not. Some condensers have the high pressure cut-out switch externally accessible. Look for a button sticking out of the cabinet in the vicinity of the refrigerant pipes. Press it in. If the machine starts up, the head pressure got too high, possibly from turning on and off too quickly, too much or too little refrigerant, or an electrical interruption. As the unit ages, the switch can weaken and pop easily. If the condition repeats itself often, have a serviceman check it.
Because all the controls are internally mounted and high voltage wiring is exposed, only a serviceman should open panels.

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Hydro-Air Systems

Basic troubleshooting:

Make sure that the thermostat is set higher than the actual room temperature. If the system has central air, or the system is zoned, make certain that the selector switch is on heat. If the thermostat is programmable, fresh batteries might be needed. Hot water must circulate through the pipes and coil before heat can be produced, so allow time for this to take place.
Make sure that the emergency switch (usually a red switchplate at the top of the basement stairs or at the side of the boiler), is on. There might be a switch on the air handler to check. An oil burner will have a red button on the protecto relay mounted on the burner. Press it only once. If it does not fire and continue to run, call for service. Resetting the button repeatedly can create an explosive condition.
If the system has central air, move the fan switch on the thermostat from "auto" to "on." If the blower runs, it proves power at the air handler. If warm air flows out of the registers, the aquastat could be out of adjustment or the time delay is malfunctioning. If the blower does not run and there is power to the air handler, a control has burned out or the blower motor needs checking. Do not put fingers or hands in the blower. Aside from sharp edges, it could start up unexpectedly and cause a serious injury.
Many air handlers have a safety switch that shuts off power if the door is removed. Check that the door is correctly installed.

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Oil Furnaces

Basic troubleshooting:

First check that the thermostat is set higher than the actual room temperature. If you have a programmable thermostat, check that it has fresh batteries.
If equipped with central air, or the system is zoned, make certain the selector switch is on heat.
Check that the emergency switch (usually a red switch plate at the top of the cellar stairs or on the side of the furnace) is on.
If you are familiar with the fuse or circuit breaker panel, see if the fuse is burned or the breaker is tripped. Correct the problem once; if the fuse blows or breaker trips again, call a serviceman.
If you can access the burner, check the red button on the protecto relay. Older furnaces will have a stack limit switch mounted on the smoke pipe that connects the furnace to the chimney. Push the button one time only. Repeated attempts to fire the burner without ignition can create an explosive condition. If the burner fails to fire and continue running on its own, call for service.

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Wood Furnaces

Basic troubleshooting:

If the furnace does not have backup heat, thens controls are minimal, consisting of a thermostat, relay and fan. Most furnaces with backup heat will have a second thermostat to control the auxiliary heat.
If the furnace has backup heat that will not operate, try the following:

First check that the thermostat is set higher than the actual room temperature. If you have a programmable thermostat, check that it has fresh batteries.
If equipped with central air, or the system is zoned, make certain the selector switch is on heat.
Check that the emergency switch (usually a red switch plate at the top of the cellar stairs or on the side of the furnace) is on.
If you are familiar with the fuse or circuit breaker panel, see if the fuse is burned or the breaker is tripped. Correct the problem once; if the fuse blows or breaker trips again, call a serviceman.
If you can access the burner, check the red button on the protecto relay. Older furnaces will have a stack limit switch mounted on the smoke pipe that connects the furnace to the chimney. Push the button one time only. Repeated attempts to fire the burner without ignition can create an explosive condition. If the burner fails to fire and continue running on its own, call for service.

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