Aircon not heating? Settings, defrost cycles and real faults

The short answer: check the remote is on heat mode (sun symbol), give the system a few minutes to warm up, and know that a pause with steam from the outdoor unit on a cold morning is a normal defrost cycle — not a fault. Cold air that never turns warm, on the right setting, is a genuine fault worth a visit.

The settings trap

Most reverse-cycle “not heating” calls are mode-related: the remote is on cool, fan or dry from summer, or on auto with a set point the room has already reached. Set heat mode a few degrees above the current room temperature and give it five minutes — unlike a gas heater, a heat pump ramps up rather than blasting instantly.

The defrost cycle (normal, but alarming)

On cold, damp Melbourne mornings, ice forms on the outdoor coil. The system periodically reverses briefly to melt it — indoor airflow pauses or goes cool for a few minutes, and the outdoor unit may steam or drip. That’s designed behaviour. A system that defrosts constantly and never delivers real heat, though, has a problem worth diagnosing.

Airflow and honesty about cold nights

Clogged filters choke heating exactly like cooling — rinse them first. And on frosty nights every heat pump loses some capacity: a correctly sized system stays comfortably ahead of that, an undersized one falls behind. Sizing is covered here — it matters for winter as much as summer.

Actual faults

Persistent cold air in heat mode, error codes on the display, the outdoor unit refusing to start, or breakers tripping point to refrigerant, valve, sensor or electrical faults — none of them DIY-able. Refrigerant work requires an ARCtick licence and electrical faults a licensed electrician; our repair visits cover both, with the price quoted before any work. If the system is old and winter is its breaking point, run the repair-or-replace numbers before spending on it.