York Furnace 4 Amber Flashes (YP9C Modulating)
WarningShown as: Four amber flashes, two-second pause, repeating
The furnace has automatically cut back its heating output because airflow through the house side is restricted.
Manual wording: “Four Amber Flashes - Heating capacity is reduced due to restriction in the circulating air system. Check for dirty filter or closed registers.”
Documented for: YP9C, YPLC modulating furnaces
Likely causes, most common first
- Dirty air filter
- Closed or blocked supply registers
What you can safely check yourself
- Check and replace the air filter
- Open all supply registers and clear anything blocking the return grille
When to call a technician
If the code stays after a clean filter and open registers, the duct system or blower needs a technician.
A York furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installation Manual - Modulating ECM Residential Gas Furnace with ECM Motor, Models YP9C*C / TP9C*C / CP9C*C / LP9C*C (Up to 98% Modulating Multi-position), 1083292-UIM-A-0114 (Johnson Controls Unitary Products (York), YP9C*C (York Affinity modulating), and the identical TP9C / CP9C / LP9C chassis) · checked 2026-08-25