When a heat pump fails to blow hot air in heating mode, the issue can stem from several mechanical, electrical, or control configuration faults. A frequent culprit is a stuck reversing valve, which prevents the system from shifting its refrigerant cycle from cooling into heating mode. Another common cause is a malfunctioning defrost cycle, where ice buildup on the outdoor coil triggers a safety lockout or leaves the unit trapped in defrost mode, blowing lukewarm air. Additionally, a faulty thermostat setting, a tripped circuit breaker for the outdoor unit, low refrigerant levels from a leak, or a failed auxiliary heating strip can prevent proper warmth. You can verify the cause by checking outdoor coil icing, ensuring thermostat wiring is secure, and confirming that the outdoor condenser fan and compressor are actively running.
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