How to Fix a Heat Pump That Shows a Flashing Light but No Error Code

A flashing light on your heat pump without an accompanying error code is more common than you might think, and in many cases it points to something straightforward you can sort out yourself. That said, some causes do require a licensed professional — so it's important to work through the possibilities carefully before reaching for a screwdriver.

What Does a Flashing Light Without an Error Code Usually Mean?

Most heat pump brands (Mitsubishi Electric, Daikin, Fujitsu, Panasonic, and others sold widely in New Zealand) use flashing indicator lights to signal that the unit has detected an abnormal condition. When no error code appears on the indoor display or remote, it typically means:

• The unit is in a temporary protection or standby mode (not a fault per se)
• A minor sensor or communication issue has been detected
• The unit is defrosting (normal in cold weather)
• There's a power supply irregularity
• The filter or airflow is restricted

Before assuming the worst, work through the steps below.

Step 1: Check the Defrost Cycle

In New Zealand winters — especially in the South Island, Wellington, and elevated areas — heat pumps regularly enter a defrost cycle. During this cycle, the outdoor unit frosts up and the system temporarily reverses to melt the ice. You may see:

• A flashing operation or timer light
• Reduced or no airflow from the indoor unit
• Steam rising from the outdoor unit

This is completely normal. Wait 5–15 minutes. If the unit resumes normal operation, no action is needed.

Step 2: Power Cycle the Unit

A simple reset clears many temporary faults:

1. Turn the heat pump off at the remote or wall controller.
2. Switch off the dedicated isolator switch (usually near the indoor unit or on the wall nearby).
3. Go to your switchboard and turn off the heat pump circuit breaker.
4. Wait a full 5 minutes.
5. Restore power at the switchboard, then the isolator, then turn the unit on via the remote.

If the flashing light disappears and the unit runs normally, the fault was likely a transient power glitch.

Step 3: Clean or Check the Air Filters

Blocked filters are one of the most common causes of heat pump protection modes. A restricted airflow triggers the unit to shut down or flash a warning.

• Remove the indoor unit filter panels (refer to your owner's manual — most slide or clip out without tools).
• Wash filters gently with warm water, allow to dry fully, and refit.
• Check that no furniture, curtains, or objects are blocking the indoor or outdoor unit.
• Ensure the outdoor unit has at least 30 cm of clear space around it and is not clogged with leaves, grass clippings, or debris.

Regular filter cleaning every 4–6 weeks is recommended by most manufacturers and aligns with good practice under the Healthy Homes Standards for rental properties.

Step 4: Check the Remote Control and Settings

• Replace the remote control batteries — a low battery can cause erratic signals and trigger protection modes.
• Make sure the unit isn't set to a conflicting mode (e.g., cooling mode in winter when the outdoor temperature is too low for that mode to operate).
• Check that the timer function hasn't been accidentally activated.

Step 5: Inspect for Obvious Physical Issues

Do a visual check — safely, without removing panels or touching electrical components:

• Is the outdoor fan spinning when the unit is running?
• Is there any ice build-up on the outdoor unit outside of a normal defrost cycle?
• Are there any unusual noises — grinding, rattling, or hissing?
• Is the condensate drain (the pipe that removes moisture from the indoor unit) blocked or overflowing?

A blocked condensate drain can trigger a float switch that shuts the unit down. You may be able to clear a minor blockage by flushing the drain pipe with water, but check your manual first.

Step 6: Consult Your Owner's Manual and Manufacturer

Every brand uses slightly different flash patterns. Your owner's manual will have a fault-finding table — count the number of flashes and the pattern (e.g., 3 flashes, pause, 3 flashes). Even without a code on the display, the flash pattern itself is often a diagnostic code. If you've lost your manual, most manufacturers publish them on their NZ websites or you can contact their local support line.

For general guidance on heat pump performance and energy efficiency, Energywise has useful NZ-specific resources.

When to Call a Professional

Stop DIY troubleshooting and call a licensed heat pump technician if:

• The flashing light persists after all the above steps
• You notice ice on the indoor unit or refrigerant lines (not just the outdoor unit in winter)
• There is a hissing or bubbling sound that could indicate a refrigerant leak
• The unit trips the circuit breaker repeatedly
• You smell burning or see any signs of electrical scorching
• The outdoor fan is not spinning when the unit is operating

Important safety note: Heat pump electrical work, refrigerant handling, and internal component repairs are restricted work under New Zealand law. Refrigerant handling requires an approved handler certificate. Electrical connections must be carried out by a registered electrician — see the Electrical Workers Registration Board (EWRB) for what's restricted. Never open the electrical panel or attempt to recharge refrigerant yourself.

For compliance and building consent questions related to heat pump installation, MBIE Building Performance is the authoritative source.

You can find qualified, local heat pump installers and technicians on tradedirectory.co.nz to get the job sorted safely and correctly.

Sources & Further Reading

• Energywise – Heat Pumps
• MBIE Building Performance – Building Code
• Electrical Workers Registration Board – Restricted Work
• Tenancy Services – Healthy Homes Standards
• WorkSafe NZ – Electrical Safety
• BRANZ – Building Research