LDMEDIUM
Low Fire Pressure Switch (Carrier/Bryant)
Low fire pressure switch not closing during modulated heat operation, specific to Carrier and Bryant two-stage and modulating furnaces.
What This Error Code Means
The low-fire pressure switch isn't detecting sufficient draft during low-stage heating.
Common Causes
- Vent pipe partially blocked
- Draft inducer motor running slow on low speed
- Pressure switch hose kinked
- Defective low-fire pressure switch
- Excessive vent length or elbows
Affected Brands
CarrierBryant
How ROMA Heating Fixes This
- Check vent pipe for restrictions
- Test draft inducer on low speed tap
- Inspect pressure switch hoses
- Replace low-fire pressure switch
- Verify proper operation in both stages
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