If you smell burning or hot electrics
Turn the heat pump off at the remote, then at its isolating switch or the switchboard, and don't use it again until it's been checked. Don't open the indoor or outdoor unit to hunt for the cause. Electrical faults are for a registered and licensed electrical worker, and a heat pump repair specialist can track down what's overheating.
Musty, stale or damp smells
A stale or musty smell when the heat pump starts up is a sign the inside of the indoor unit needs cleaning. Samsung NZ sets out a sensible order to tackle it in, below.
Clearing a musty smell
Air the room
Open windows or doors and let fresh air through while you work.
Run Fan mode
Samsung NZ suggests running the heat pump on Fan mode for 3 to 4 hours.
Check the drain
Cleaning the drain is Samsung NZ's next step. For an owner, that means making sure the hose outside runs downhill, isn't squashed, and doesn't end in a puddle or a pile of leaves.
Wash the filters
Take them out and clean them as your manual says, and let them dry before they go back in.
Run the self-clean
If your model has a Self Clean or Auto Clean function, Samsung NZ suggests running it last.
If the smell comes back
Samsung NZ says persistent odours may need a professional clean of the indoor unit. That means opening it up to clean the coil, the fan and the drain tray, a job for someone who does heat pump cleaning week in, week out.
If the whole house smells damp, not just the heat pump, the fix is usually ventilation and heating working together. Consumer NZ says Dry mode does remove moisture, but a purpose-built dehumidifier does it better. Our home ventilation page explains the options.
Dusty smell when you first switch on for winter? Clean the filters before anything else. Mitsubishi Electric NZ suggests doing that at every change of season anyway.
Which noises are normal?
Samsung NZ says some airflow and fan noise is normal, especially at start-up. Consumer NZ says the fans in both units run whenever the heat pump is on, but the indoor unit should settle to a low hum once the room is up to temperature.
Outside is louder. Consumer NZ says the outdoor unit can be quite noisy, and on frosty mornings the heat pump also stops heating for short spells while it clears ice, which Mitsubishi Electric NZ says is normal.
If you're comparing models, some Zoned Energy Rating Labels show noise at full power, near the indoor unit and near the outdoor unit, and Consumer NZ says the lower the number, the quieter. For scale, EECA puts a quiet home at about 30 dBA, a typical conversation at 60 and a running vacuum cleaner at 75.
What the noise might mean
| Likely meaning | What to do | |
|---|---|---|
| Soft hum or rush of air from the indoor unit | Normal fan and airflow noise (Samsung NZ) | Nothing, unless it gets louder over time |
| Louder at start-up, then quieter | Normal: the indoor unit should drop to a low hum once the room's warm (Consumer NZ) | Nothing |
| Rattle, buzz or vibration | Something loose, or a unit that isn't sitting firmly. BRANZ says units should be stable, with sound and vibration insulation that works | Check from the ground that nothing's touching it, then book a technician |
| Grinding, squealing or a new rumble | Worn moving parts. BRANZ says to maintain the outdoor unit so worn bearings don't become noisy | Switch it off and book a service or repair |
| Fine to you, loud next door | An outdoor unit close to a boundary or a bedroom window | Talk to the neighbours, then ask an installer about moving it |
When the noise bothers the neighbours
Where the outdoor unit sits matters most here. BRANZ advises keeping outdoor units away from quiet areas like bedrooms, and Consumer NZ says to think about the neighbours if yours has to go near the boundary.
Noise limits are set in each council's district plan, and Auckland's, for example, vary by zone and by time of day. A council building sign-off for the unit doesn't stop the council acting on a noise problem later.
There's a warranty angle too. Black Diamond Technologies excludes issues from Mitsubishi Electric outdoor units installed close to neighbouring boundaries or other noise-sensitive spots. Moving a unit is a job for an installer, with a registered electrician for the electrical side, and our consents and noise guide covers the rules.
Before you call about a noise
Pin down where and when
Indoor or outdoor unit? At start-up, all the time, or only on frosty mornings? A short phone video helps the technician hear what you hear.
Look, don't poke
From the ground, check nothing is resting against the outdoor unit, rubbing it or rattling beside it. Move anything parked against the casing: Mitsubishi Electric NZ's owner guide wants the space around it kept clear anyway.
Clean the filters
Clogged filters restrict the airflow the fan has to push. Clean them the way your manual says.
What's yours to do, and what isn't
You can
- Airing the room and running Fan mode for a musty smell.
- Washing or vacuuming the filters.
- Making sure the drain hose outside isn't blocked or sitting in water.
- Moving anything that's touching or crowding the outdoor unit.
- Switching off at the isolating switch or switchboard if you smell burning.
Leave to a licensed installer
- A deep clean of the coil, fan and drain tray inside the indoor unit.
- Tracing rattles, worn bearings and fan faults.
- Re-mounting a unit that vibrates, or moving one that's too close to a bedroom.
- Any electrical fault, by a registered electrical worker.
What we'd do
Our take
For a musty smell, we'd air the room, clean the filters and run through Samsung NZ's steps before paying anyone. If it's back within a few weeks, we'd book a professional clean rather than live with it. A burning smell, or a grinding or squealing noise that wasn't there last winter, we'd switch off straight away and get a technician out, because those don't get better on their own.