Responded to no heat complaint for 25+ year old furnace that was cycling without ignition. Bypassed furnace control board temporarily to restore heating function. Upon removing bypass clippers, unit continued to operate normally. Performed comprehensive diagnostics including gas pressure verification, carbon monoxide testing, and heat exchanger inspection with no hazardous conditions found. Cleaned flame sensor and checked pressure switch and flame rollout switches. Discovered extremely dirty furnace filter clogged with pet fur and dirt causing airflow restriction. Educated homeowner on proper filter maintenance, condensation trap cleaning, and keeping furnace area clear of obstructions. Unit now functioning properly.
