224
Easy Fix
Lennox · HVAC Systems (AC, Furnaces & Heat Pumps)
Secondary Voltage Fuse Open
Quick Answer
Error code 224 on your Lennox HVAC Systems (AC, Furnaces & Heat Pumps) means: Secondary Voltage Fuse Open. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Likely Causes
How to Fix It
1
Locate and check the 3A or 5A fuse on the furnace control board
2
Disconnect all thermostat wires at the furnace and replace the fuse
3
If the new fuse holds with thermostat wires disconnected, reconnect one wire at a time to find the short
4
Check outdoor unit contactor coil resistance and wiring
5
Inspect all low-voltage wiring runs for rodent damage or contact with sharp edges
Pro Tip
This is a common issue that most users can resolve without specialized tools. Try the first step before moving on to more complex solutions.
Parts You May Need
3A or 5A automotive-style fuse
24V transformer (if damaged)
Thermostat wire
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