HVAC Error Codes & Diagnostic Codes

HVAC error codes and diagnostic codes: find what a code means and how to fix it. Search by code, model number or problem, or browse by brand.

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Homeowner help: common problems

• Furnace Not Turning On: What to Check
• Furnace Blinking Light: What the Flash Codes Mean
• Tankless Water Heater No Hot Water: What to Check
• AC Running But Not Cooling: What to Check
• Heat Pump Not Heating or Blowing Cold Air
• Boiler Not Heating: What to Check
• Gas Fireplace Won't Light or Stay Lit

Specs and setup data

• Minimum clearances to combustibles Carrier · Furnace · 59TP6A
• Minimum clearances to combustibles Carrier · Furnace · 59SC6A
• Filter sizes by casing width Carrier · Furnace · 58SB0A/58SB1A
• Filter sizes by casing width Carrier · Furnace · Payne PG96VTA
• Filter sizes by casing width and filter cabinet Carrier · Furnace · 59SC6A
• Filter sizes by casing width and filter cabinet Carrier · Furnace · 59TP6A
• Normal status displays (7-segment) Daikin · Furnace · Daikin DR96TN/DD96TN
• Installation clearances FlowMax · Combi Boiler · FlowMax condensing combi (FLOWMAX-90/120)
• Hot water scald risk by temperature FlowMax · Combi Boiler · FlowMax condensing combi (FLOWMAX-90/120)
• Operating range and service space Fujitsu · Heat Pump · Fujitsu multi-zone outdoor 18/24 type
• Minimum recommended filter size Goodman · Furnace · Goodman/Amana GM9C96/AM9C96
• Normal status displays (7-segment) Goodman · Furnace · Goodman/Amana GM9S96/AM9S96

Troubleshooting without an error code

• Not cooling All brands · Air Conditioner
• Amber STATUS or green COMM light not on Carrier · Air Conditioner
• Compressor will not run - winding and electrical checks - Carrier split systems Carrier · Air Conditioner
• Delay before the compressor restarts Carrier · Air Conditioner
• Hissing from the outdoor unit after it shuts off Carrier · Air Conditioner
• Outdoor unit unresponsive after several faults Carrier · Air Conditioner
• Superheat too high or too low on TXV system - Carrier split systems Carrier · Air Conditioner
• Two-stage unit not changing stages - Carrier 24ANB/25HNB/25HCB6 Carrier · Air Conditioner
• No cooling - R-32 GLXS/ALXS condenser Goodman · Air Conditioner
• Checking OAT and OCT thermistors - KeepRite C4A3/CXA6 KeepRite · Air Conditioner
• Low cooling capacity - check airflow and charge - Lennox EL16KC1 Lennox · Air Conditioner
• Outdoor unit will not start - Lennox EL16KC1 Lennox · Air Conditioner