The float switch in your heat pump's indoor unit is a small but important safety device — it detects when the condensate drain tray is overflowing and shuts the unit down before water damage occurs. Testing it is a straightforward process most homeowners can do safely, though any electrical repairs or refrigerant work must be left to a licensed professional.
What Does a Float Switch Do?
During normal operation, your heat pump produces condensate (water) as it cools or dehumidifies the air. This water drips into a condensate drain tray and flows away through a drain pipe. If that pipe blocks up, water builds in the tray. The float switch sits in the tray and rises with the water level — once it reaches a set point, it sends a signal to shut the unit off, preventing overflow and potential ceiling or wall damage.
A float switch that isn't working correctly may either:
- Fail to shut the unit off when the tray fills (risking water damage), or
- Trigger a false shutdown even when the tray is dry (causing unnecessary downtime).
Safety First
Before you do anything near your heat pump's indoor unit, switch the unit off at the wall controller and isolate it at the circuit breaker. While the float switch itself is low-voltage in most systems, you are working near electrical components. Never probe wiring or internal terminals unless you are a licensed electrician. Under the Electrical Workers Registration Board (EWRB) rules, electrical inspection and repair work on fixed wiring is restricted work — homeowners cannot legally carry it out.
Tools You May Need
| Item | Purpose |
|---|---|
| Torch/headlamp | Inspect the drain tray and float |
| Small cup or jug of water | Manually raise the float |
| Multimeter (optional) | Check switch continuity if accessible |
| Dry cloth or towel | Mop up any spills |
Step-by-Step: Testing the Float Switch
1. Locate the Float Switch
Remove the front panel of your indoor unit (usually a clip-on cover — consult your owner's manual). The float switch is typically a small plastic component sitting in or beside the condensate drain tray, connected by two thin wires. It may be white, black, or clear.
2. Check for Obvious Issues
With your torch, inspect the tray and float for:
- Visible mould, slime, or debris blocking the float from moving freely
- A float that is already stuck in the raised position (this would cause a false shutdown)
- Cracked or broken float housing
- Disconnected wires
If the tray has standing water in it, your drain is likely blocked — clear that first before testing the switch.
3. Manual Float Test
With the unit powered off, carefully pour a small amount of water into the condensate tray (just enough to raise the float). Then restore power and try to run the unit. If the float switch is working correctly, the unit should not start (or should shut off quickly) because the float is in the raised/triggered position.
Once you've confirmed this, power the unit off again, drain or mop up the water, and restart — the unit should now run normally.
Note: On some units the float switch triggers an error code on the display (common codes include E1, E4, or similar — check your manual). This is a useful confirmation the switch is communicating with the control board.
4. Continuity Check (Optional — for Confident DIYers)
If you own a multimeter and the float switch wiring connector is accessible without touching fixed wiring, you can disconnect the float switch connector and test continuity across its terminals:
- Float down (dry tray): The circuit should be closed (continuity present) — the unit is allowed to run.
- Float up (raised manually): The circuit should be open (no continuity) — the unit is told to stop.
If your results are the opposite, or you get no change at all, the switch is likely faulty and needs replacing.
Common Reasons a Float Switch Triggers
- Blocked condensate drain pipe — the most frequent cause; clear it with a wet/dry vacuum or a thin flexible brush
- Dirty air filter — restricts airflow, causing the coil to ice up and produce excess meltwater
- Unit installed out of level — water pools rather than draining; check with a spirit level
- High humidity conditions — common in NZ coastal and northern regions during summer
Regular filter cleaning (every 4–6 weeks during heavy use) and an annual service go a long way toward preventing float switch nuisance trips. BRANZ recommends keeping heat pump components well maintained to preserve indoor air quality and system efficiency — relevant under the Healthy Homes Standards for rental properties.
When to Call a Professional
Call a licensed heat pump installer or refrigeration technician if:
- The float switch tests as faulty and needs replacing (involves disconnecting wiring)
- The unit keeps tripping even after you've cleared the drain and cleaned filters
- You notice ice forming on the indoor coil
- There is any sign of water damage to ceilings, walls, or the unit itself
- You are unsure about any step above
Under the EWRB regulations, replacing or rewiring a float switch connected to fixed wiring is restricted electrical work and must be done by a registered electrician or authorised person. Many heat pump installers hold the relevant electrical registration — always ask before they start work.
You can find qualified local heat pump installers and refrigeration technicians on tradedirectory.co.nz.
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