Quick answer
Long run times are normal. An inverter heat pump is designed to run for hours at low speed rather than switching on and off the way a furnace does, and near the coldest temperatures it will run continuously by design. It is only a fault if the house is not holding its setpoint, the backup heat indicator stays on, or the unit runs flat out in mild weather.
Homeowners who move from a gas furnace to a heat pump almost always ask this in the first winter, because the sound never stops. A furnace blasts and quits; a heat pump idles along. Constant running is usually the machine doing its job well. The useful skill is knowing the three signs that separate normal long runtimes from a system that is running because it cannot keep up.
Running long is the design, not a symptom
An inverter compressor modulates its output across a wide range instead of being either fully on or fully off. Running at a low, steady rate that just matches the house's heat loss is more efficient than repeatedly starting at full power, and it holds the temperature more evenly from room to room. As outdoor temperatures approach the design conditions the equipment was sized for, 100 per cent runtime is the arithmetic working out exactly as intended.
The three checks that tell you whether it is a problem
- Is the thermostat holding its setpoint? If the room reads what you asked for, the system is winning and the runtime is irrelevant.
- Is the auxiliary or emergency heat indicator lit? Occasional aux on a cold night is normal; aux showing for hours, or in mild weather, is not.
- Is the supply air warm to the back of your hand at the register? Heat pump supply air is cooler than furnace air by nature, but it should be clearly above room temperature — why is my heat pump blowing cold air in heating mode covers that distinction.
Running constantly and falling behind
- Low refrigerant charge from a leak. The compressor runs without moving much heat, and the outdoor coil may frost in weather that should not cause it. Finding and sealing the leak is the repair; topping it up is not.
- Restricted airflow — a filter left in too long, a matted indoor coil, or closed and blocked registers. A heat pump is more sensitive to this than the furnace that used to sit in the same cabinet.
- Duct leakage into unconditioned space. A trunk crossing an attic or a garage bulkhead delivers a share of your heat outside the envelope, so the unit never catches up.
- A defrost cycle stuck on, or repeating far more often than the weather warrants, which reverses the system for minutes at a time.
- Undersized equipment or a load that has changed since it was sized — a finished basement, an addition, or windows and doors left open in a mild spell.
- A blocked outdoor coil: drifted snow, packed leaves, or a fence and hedge closer than the manufacturer's clearance.
Running constantly in mild weather
In autumn or spring a system that never stops usually points at controls rather than capacity. A thermostat set to a fan mode of On keeps the blower turning between calls, which sounds like continuous operation even when the compressor is idle — switch the fan to Auto and listen again. A staging or lockout setting that keeps the unit pinned at high output does the same thing more expensively. In cooling season, longer cycles in humid lake air are desirable, since a short cycle cools without dehumidifying.
The expensive version of this problem
The costly case is not the compressor running — it is the backup heat running alongside it. Electric elements or a furnace held on by a badly set lockout, or an emergency heat switch nobody turned off in the spring, will quietly add far more to the bill than the compressor ever could. Pull up the thermostat's runtime history; most connected models break out heat pump hours from auxiliary hours, and the pattern is usually obvious. How much electricity a heat pump uses puts those hours into kilowatt-hours.
What a technician measures on this call
- Refrigerant charge verified by subcooling and superheat rather than by pressure alone.
- Static pressure across the air handler and the temperature rise across the coil, which together expose an airflow restriction.
- Compressor amp draw compared against the nameplate rating on the outdoor unit.
- A forced defrost, timed, with the coil sensor and control board checked.
- Thermostat configuration: staging, compressor lockout, backup lockout, and whether the equipment type was ever set correctly at commissioning.
A diagnostic visit runs $90–$150 and is credited toward the repair if you proceed, and the common electrical parts behind this kind of call — a capacitor or contactor — sit at $150–$350. If the unit was oversized or undersized from the start, no repair fixes that; see what size heat pump do I need for what a correct sizing looks like.
ZK Mechanical diagnoses heat pumps across Burlington, Oakville, Hamilton and the wider GTA, and we will tell you when the answer is that your system is working the way it should. Book heat pump repair or send us the details and we will take a look.