Why Auckland heat pumps play up
Inland nights sit right on the defrost line
EECA says frosting starts once it's below 5.5 degrees outside, and some heating capacity goes to defrosting the outdoor coil. July's mean low is 5.6 degrees at Henderson North and 5.4 at Ardmore Airport, so winter defrost pauses are routine in west and south Auckland. At the airport, with a July mean low of 7.7, they're less common.
Damp air makes more ice
Mitsubishi Electric NZ says the more moisture in the air, the more freezes on the outdoor coil. With mean 9 am humidity of 82% at Auckland Airport, a still, frosty morning can bring longer or more frequent defrosts than the temperature alone suggests.
Salt on coils and fins
BRANZ found sheltered spots on a building near an Auckland harbour gathered about 3 to 8 times more salt than exposed ones. Corrosion on the outdoor coil or casing builds slowly, and several warranties exclude it: Rinnai NZ, LG and Gree NZ all leave out damage from corrosive or weathering conditions.
Winter gales and westerly squalls
NIWA says gales are most frequent in winter, and gusty westerlies with thunderstorms are most likely in winter and spring. Flying debris, a shifted bracket or leaves packed against the coil can all stop a heat pump working well. BRANZ says outdoor units should be stable and maintained so worn parts don't get noisy.
Humid summers fill the drain
NIWA says cooling demand peaks in an Auckland summer, and on cooling the indoor unit wrings water out of humid air. Samsung NZ says most leaks come from a blocked or kinked drain hose or the wrong slope.
Burning smell, sparks, or a switch that keeps tripping
Switch the heat pump off at the remote and the switchboard, and leave it off. Don't take covers off either unit or touch any wiring. Electrical faults are for a registered electrical worker, and the refrigerant circuit is for a trained heat pump technician.
Checks to try on a cold Auckland morning
Wait out a defrost
Mitsubishi Electric NZ says a heat pump stops heating for short periods in Defrost Mode, and Consumer NZ says the outdoor unit may need a few minutes. Check it's on Heat, too: the unit isn't heating at all on Dry.
Look at the outdoor unit after a storm
Clear leaves and rubbish from around it without opening anything. BRANZ wants at least 500 mm clear on the air inlet and outlet faces.
Note the code and the model number
Samsung NZ says to write down any error code, and a blinking light on the indoor unit can signal one too. Our error codes guide shows where the brands keep their manuals.
What makes a repair bigger or smaller
The small end is a blocked drain, a filter choked after a dusty summer or a reset after a power cut. The big end is a refrigerant leak that has to be found and sealed, a corroded outdoor coil, or a fan motor or circuit board to replace. Our national heat pump repairs page goes through the common faults.
Corrosion is where your rights matter most. A warranty may exclude it, but under the Consumer Guarantees Act a heat pump bought from a business must still be of acceptable quality, including durable, and the business can't limit that to the warranty's terms.
If the unit has never kept the room warm on a frosty night, suspect size rather than a fault. BRANZ says an undersized heat pump runs constantly and defrosts again and again, and no repair changes that.
Questions to ask the repairer
- Is this a fault, or normal defrost behaviour for this weather?
- Is there corrosion on the coil or casing, and does my warranty cover it?
- If it's short of refrigerant, where is it escaping, and how will that be sealed?
- Is the outdoor unit fixed firmly enough for winter gales?
- Is this a quote or an estimate, and is there a fee for the visit?
What we'd do
Repair or replace, Auckland style
We'd always rule out defrost, the mode and a blocked drain before paying for a visit. If one part has failed on a unit that has always kept up, we'd repair it. But on a unit near the harbour with a badly corroded coil and no corrosion cover, we'd get a replacement quote alongside the repair one, with corrosion protection specified properly this time.