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Furnaces
3 OPERATIONAL ISSUES AND DIAGNOSTICS
This section has tables showing the main causes for furnace issues. The Operational Issues table helps you
identify a range of furnace operational issues and the potential servicing solutions associated with those issues.
The Diagnostics table links specific furnace components to the diagnostic tasks associated with that component.
Remember to check the basics before replacing any parts, such as loose wiring and overall heating issues. Refer
to the Maintenance (on page 41) and Heating Issues (on page 26) sections for more detail.
Review the operational issues table for a list of potential operational issues, possible solutions, and servicing
procedure links. Refer to the Diagnostics Table (on page 5) for links to specific diagnostic information on the
furnace components, for confirmation of the operational issue.
Operational Issues Table
Operational Issue
Potential Reason
Page
Motor does not run
Defective motor
36
Defective external relay
37
Fan motor runs but no spark
Low DC voltage
26
Defective circuit board or ignitor on the circuit board
32
Combustion wheel is loose
33
Electrode is defective or out of adjustment
34
Defective limit switch
35
Defective motor
36
Defective sail switch
38
Furnace sparks but does not ignite
Gas pressure issue
26
Defective circuit board
32
Electrode is defective or out of adjustment
34
Defective gas valve
39
Orifice issue
39
Motor vibrates or is noisy
Blower wheel is damaged
31
Blower wheel is dirty
41
Loose object inside the blower wheel
31
Motor mount is loose
36
Motor sha is damaged
36
Burner ignites then locks out
Low gas pressure
26
Defective circuit board
32
Combustion wheel is loose
33
Electrode is defective or out of adjustment
34
Furnace is limiting
Installation issue 26/see specific furnace installation instructions
Ducting issue 26/see specific furnace installation instructions
Return Air issue 26/see specific furnace installation instructions
Defective limit switch
35
Fan and burner turn off
Defective external relay
37
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