A vibrating heat pump outdoor unit is one of the most common complaints from NZ homeowners — and the good news is it's usually fixable without a full service call. The noise and movement are typically caused by normal compressor vibration transferring through the mounting bracket or refrigerant pipes into your wall or floor. Here's how to diagnose and fix the problem, and when to call in a professional.
Why Does the Outdoor Unit Vibrate?
Heat pump outdoor units contain a compressor — a motorised pump that cycles refrigerant. Compressors vibrate by nature, and that vibration can travel through:
- The mounting bracket bolted to the wall or sitting on a concrete pad
- Refrigerant pipes (also called line sets) that run from the outdoor unit through the wall
- Electrical conduit or drain hose if they're in contact with the cladding
Vibration tends to worsen as units age, when refrigerant charge is low, or when a bracket works loose over time.
Step 1 — Check and Tighten the Mounting Bracket
Before buying any products, do a visual inspection:
- Check all bracket bolts and screws are tight. Wall-mounted brackets can work loose over months of vibration.
- Look for cracked or missing wall plugs — especially in older brick, concrete block, or fibre-cement cladding.
- Make sure the bracket is level. A unit sitting at an angle can cause uneven compressor loading and extra vibration.
Safety note: If your unit is mounted at height, use a stable ladder and have someone hold it. Never lean out over a roof edge without appropriate fall protection. For high or difficult-to-access installations, leave this to a professional.
If the wall plugs or fixings look damaged, replace them with the correct type for your wall material. PlaceMakers and Bunnings stock a wide range of masonry anchors and stainless fixings suitable for NZ conditions.
Step 2 — Fit Anti-Vibration Pads or Mounts
Anti-vibration pads are the most effective and affordable fix. These are dense rubber or neoprene pads placed between the outdoor unit feet and the bracket, or between the bracket and the wall.
- For ground-mounted units on a concrete pad, place rubber anti-vibration pads under each foot of the unit.
- For wall-bracket-mounted units, look for anti-vibration rubber washers or grommets that fit between the bracket and the wall surface, and between the unit feet and the bracket arms.
- Some installers use spring isolators for particularly stubborn vibration — these are more effective but also more expensive.
Anti-vibration pads are available at Mitre 10 and Bunnings. Check the load rating on the packet matches your unit's weight (usually listed on the unit's data plate).
Step 3 — Isolate the Refrigerant Pipes from the Wall
Refrigerant pipes are a surprisingly common vibration path. If the line set runs along or through the wall without isolation, compressor vibration travels straight into the structure.
- Make sure pipe insulation (the foam lagging) is intact and not compressed against the wall.
- Where pipes pass through the wall, check there is a rubber grommet or foam sleeve in the penetration hole — not just a hard plastic conduit pressed against the pipe.
- Use pipe clips with rubber inserts (not bare metal clips) to secure the line set to the wall. Replace any bare metal clips you find.
Important: Do not cut, disconnect, or modify refrigerant pipes yourself. Refrigerant handling is restricted work under NZ law and must only be carried out by a registered refrigeration or heat pump technician. Check with MBIE or your technician for more on restricted mechanical work.
Step 4 — Check the Electrical Conduit and Drain Hose
Sometimes the culprit isn't the unit itself — it's the electrical conduit or condensate drain hose rattling against the cladding. Run your hand along these while the unit is running (keeping clear of moving parts) to feel for vibration transfer. Adding a small foam sleeve or repositioning a clip is often all it takes.
Step 5 — Consider a Ground Mount Instead
If your unit is wall-mounted and vibration is persistent, it may be worth asking your installer about relocating it to a ground-mounted concrete pad. Ground mounts naturally dampen vibration better than wall brackets, and they're often easier to service. This is a job for a qualified heat pump installer.
Vibration vs. Unusual Noise — Know the Difference
| Symptom | Likely cause | Action |
|---|---|---|
| Low hum through wall | Normal compressor vibration | Anti-vibration pads |
| Rattling or clanking | Loose panel, fan blade, or debris | Call a technician |
| Vibration only at startup/shutdown | Normal compressor cycling | Usually no action needed |
| Loud grinding or squealing | Failing fan motor or compressor | Call a technician urgently |
If you hear rattling, grinding, or squealing, switch the unit off and call a professional — these sounds can indicate a fault that, if ignored, may cause expensive damage.
When to Call a Professional
Call a licensed heat pump installer or refrigeration technician if:
- Tightening the bracket and fitting anti-vibration pads doesn't resolve the vibration
- You suspect the compressor itself is faulty
- The unit needs to be relocated or re-mounted
- You hear unusual mechanical noises beyond normal hum
- Refrigerant pipes need to be moved or re-routed
Refrigerant work is legally restricted — only registered technicians may handle refrigerants in NZ. You can find qualified local heat pump installers on tradedirectory.co.nz.
For rental properties, note that Tenancy Services Healthy Homes standards require heating appliances to be maintained in good working order — so landlords should address persistent vibration issues promptly.
ISO 9001
