How to troubleshoot a heat pump that is not heating or cooling (2026)
Quick Answer
If a heat pump is not heating or cooling, start with the simple checks: confirm the thermostat settings, make sure the indoor and outdoor units have power, and inspect or replace a dirty air filter. If airflow is blocked, the outdoor unit is iced over, or the system still will not run after basic checks, stop there and arrange service, because refrigerant, electrical faults and many internal component problems need a qualified HVAC professional.
Safety first
- Turn the system off at the thermostat before removing or cleaning filters.
- Do not remove access panels or touch internal wiring, capacitors or terminals.
- Do not keep resetting a breaker that trips again; leave the system off and call a professional.
- Do not handle refrigerant lines or attempt to top up refrigerant yourself.
- If you smell burning, see smoke, notice scorched components or hear loud electrical buzzing, shut the system down if safe and seek urgent professional help.
- Do not chip ice from the outdoor unit with tools or pour boiling water on it, as this can cause damage and injury.
When to call a professional: Stop and contact a qualified HVAC professional if the breaker trips again, the unit is heavily iced, only one mode works, there is a burning smell, smoke, water leaking inside, hissing or suspected refrigerant leak, exposed or damaged wiring, repeated lockouts, or the system still does not heat or cool after you have checked settings, power and filters.
Overview
A heat pump that is not heating or cooling often has a basic control, power or airflow problem rather than a major failure. Common causes include the thermostat being set incorrectly, tripped breakers, a disconnected outdoor shut-off, clogged filters, blocked indoor vents, a dirty or obstructed outdoor unit, or a system that has gone into defrost or safety lockout. In cold weather, some reduction in heating performance can be normal, but a complete loss of heating or cooling is not. The safest approach is to check the easy external items first, then stop before opening panels or handling electrical or refrigerant parts. That order matters: many heat pump faults can look similar, but checking settings, power and airflow first can restore operation quickly and may also prevent damage from running the system under strain. If the heat pump hums but does not start, repeatedly trips a breaker, freezes up, leaks water indoors, makes burning smells, or shows an error code you cannot clear using the manufacturer instructions, the next step is professional diagnosis. This guide focuses on homeowner-safe checks only and helps you decide when a repair is likely to need a trained technician.
Who this is for
Homeowners and tenants who want to carry out safe basic checks on a ducted or ductless heat pump before calling for service.
What you’ll need
- thermostat or remote control
- manufacturer manual if available
- clean replacement air filter if your system uses one
- torch
- gloves for clearing outdoor debris
Before you start
Check whether the problem affects heating, cooling or both, and whether the indoor unit, outdoor unit, or neither appears to be running. If there is a burning smell, damaged wiring, repeated breaker trips, unusual buzzing, signs of refrigerant leak, or heavy ice build-up, do not continue beyond basic shut-down and filter checks.
Step-by-step
- 1
Confirm the control settings
Set the thermostat or controller firmly to Heat or Cool as needed, not Auto if you are trying to test one mode. Check that the set temperature is clearly above room temperature for heating or clearly below room temperature for cooling. If the thermostat uses batteries, replace them if indicated. If you have a ductless system, make sure the remote is sending commands and the unit is not in fan-only, dry or timer mode.
Why: Incorrect mode, setpoint or a weak thermostat battery is one of the most common reasons a heat pump appears not to work.
- 2
Check power to both indoor and outdoor equipment
Look at the consumer unit or breaker panel for any tripped breaker serving the heat pump or air handler and reset it once if appropriate. Also check any nearby disconnect switch for the outdoor unit to make sure it has not been switched off. If the system has a service switch near the indoor unit, confirm it is on.
Why: A heat pump usually has more than one power feed, and the indoor and outdoor sections both need power to heat or cool properly.
- 3
Inspect the air filter and airflow path
Turn the system off at the thermostat before removing the filter. Check whether the filter is visibly dirty and replace or clean it according to the manufacturer instructions. Make sure supply and return grilles are open and not blocked by furniture, curtains or dust build-up. For ductless systems, check that the indoor unit inlet and outlet are not obstructed.
Why: Restricted airflow can stop effective heating and cooling, cause icing, trigger protective shut-downs and increase wear.
- 4
Check the outdoor unit condition
With power left on unless there is a safety issue, look at the outdoor unit from the outside only. Remove leaves, rubbish or vegetation from around it and make sure the fan area is unobstructed. In winter, a brief frost pattern can be normal, but a unit encased in heavy ice is not. Do not chip ice off or pour hot water over the unit.
Why: The outdoor unit must move air freely to transfer heat. Blockage or abnormal icing can stop the heat pump working and points to a fault that may need service.
- 5
Allow time for normal delays and defrost operation
After correcting settings or restoring power, wait through the system's normal start-up delay before assuming it has failed. In heating mode, the outdoor unit may occasionally enter defrost, during which steam or water may appear and heating output can briefly change. Use the manufacturer guidance for your model to identify normal behaviour.
Why: Heat pumps often delay starting to protect the compressor, and defrost cycles can be mistaken for a fault.
- 6
Look for fault indicators and basic symptoms
Check the thermostat, wall controller or indoor unit display for an error code, flashing light or lockout message. Note what is running: indoor fan only, outdoor fan only, neither, or short cycling on and off. Also note unusual noises, water leaks or odours.
Why: These symptoms help separate a control or airflow problem from a fault involving electrical parts, condensate drainage, sensors or refrigerant.
- 7
Reset only if the manufacturer allows it
If the manual gives a homeowner reset procedure, follow it exactly once. If not, leave the system off and contact a professional rather than repeatedly cycling power or the breaker.
Why: Some faults will clear with a proper reset, but repeated restarting can worsen compressor or electrical damage.
Why this works
A heat pump relies on correct control signals, an uninterrupted power supply and adequate airflow across indoor and outdoor coils. If any of those basics fail, the system may stop heating or cooling even when major components are still intact.
Common mistakes to avoid
- Assuming the system has failed before checking thermostat mode, setpoint and timer settings
- Resetting a tripped breaker repeatedly instead of treating it as a warning sign
- Running the system with a clogged filter or blocked vents
- Trying to scrape ice off the outdoor unit or open electrical panels
- Confusing normal winter defrost with a complete heating failure
Troubleshooting
System does nothing at all
Check thermostat batteries and settings, then check breakers, indoor service switch and outdoor disconnect. If power is present and it still will not respond, arrange professional service.
Indoor fan runs but air is not warm or cool enough
Replace a dirty filter, open blocked vents, confirm the correct mode and setpoint, and allow time after changing settings. If airflow is normal but output is still weak, call a professional.
Outdoor unit is running but indoor comfort does not improve
Check filter, vents and thermostat settings first. If the problem affects both heating and cooling, a professional should check for refrigerant, sensor or reversing valve issues.
Breaker trips again after reset
Stop resetting it and leave the system off. This suggests an electrical fault that needs a qualified technician or electrician.
Outdoor unit is covered in heavy ice
Turn the system off and arrange service. Brief frost can be normal, but persistent or heavy icing points to airflow, defrost or refrigerant problems.
Heat pump cools but will not heat, or heats but will not cool
Rule out wrong mode and schedule settings first. If one mode consistently fails, professional diagnosis is needed because the issue may involve controls or the reversing valve.
Compare your options
DIY basic checks only
Best for: Settings, power and airflow issues
Pros: Fast, low cost, safe for most householders, may solve common faults immediately
Cons: Will not resolve refrigerant, electrical or internal component faults
Professional HVAC diagnosis
Best for: Persistent faults, icing, lockouts, electrical problems or one-mode failures
Pros: Can test components safely, interpret fault codes, verify refrigerant and airflow properly
Cons: Costs more than basic DIY checks and may require scheduling
| Option | Best for | Pros | Cons |
|---|---|---|---|
| DIY basic checks only | Settings, power and airflow issues | Fast, low cost, safe for most householders, may solve common faults immediately | Will not resolve refrigerant, electrical or internal component faults |
| Professional HVAC diagnosis | Persistent faults, icing, lockouts, electrical problems or one-mode failures | Can test components safely, interpret fault codes, verify refrigerant and airflow properly | Costs more than basic DIY checks and may require scheduling |
Alternatives
- Use the manufacturer troubleshooting section for your exact model before arranging service
- If you rent, report the fault to the landlord or property manager rather than attempting anything beyond basic user checks
Pro tips
- Take a photo of the thermostat settings and any error code before changing anything
- Replace filters on the schedule recommended by the manufacturer or sooner if they look dirty
- Keep the outdoor unit clear of leaves and overgrowth so airflow is not restricted
- After changing from heating to cooling or vice versa, give the system time to respond before assuming it has failed
Legal & regulatory notes
Electrical and refrigerant work is commonly restricted to qualified, licensed or certified professionals depending on local law. Follow local regulations, tenancy rules and manufacturer instructions.
What this guide does not cover: This guide covers only safe homeowner checks for common control, power and airflow issues. It does not cover electrical testing, refrigerant diagnosis or charging, compressor or reversing valve repair, duct leakage testing, detailed defrost faults, brand-specific error code interpretation, or any work that requires opening equipment panels or specialist tools.
Cost considerations
Simple fixes such as correcting settings, replacing a filter or clearing obstructions are usually far less costly than ignoring the problem and continuing to run the system under strain. Repeated breaker trips, icing and one-mode failures often indicate faults that are more economical to diagnose early before further damage occurs.
Prefer to hire a professional?
If this job is beyond a confident DIY — or the work needs to be done by a licensed professional — you can find a verified heating & cooling specialist through Trade Directory (tradedirectory.co.nz), New Zealand's directory of real, verified trade businesses. Compare local tradespeople, read their details and request quotes before you commit.
Find a heating & cooling specialist on Trade DirectoryFrequently asked questions
Is it normal for a heat pump to stop heating briefly in winter?+
Yes, during defrost the system may temporarily change how it operates and the indoor air may feel less warm for a short time. Persistent loss of heat, heavy icing or failure to recover is not normal.
Why is my heat pump running but the house is still uncomfortable?+
The most common homeowner-check items are wrong thermostat settings, dirty filters, blocked vents or an obstructed outdoor unit. If those are fine, the system may need professional diagnosis for airflow, controls or refrigerant-related faults.
Can a dirty filter stop a heat pump from heating or cooling?+
Yes. A clogged filter restricts airflow, which can reduce output, cause icing and trigger protective shut-downs.
Should I reset the breaker more than once?+
No. One reset after a nuisance trip may be reasonable, but if it trips again, stop and call a qualified professional.
Can I diagnose a refrigerant problem myself?+
Not safely or reliably. Signs such as icing, poor performance in both modes or hissing can suggest a refrigerant issue, but testing and repair should be done by a qualified HVAC technician.
Sources & references
Guidance on this page is traced to documented sources. Last checked 24 September 2026.
- AHRI - Homeowner Resources · industry
Supports homeowner-safe maintenance boundaries and the role of qualified HVAC professionals for diagnosis and repair.
Basic troubleshooting steps stay fairly stable, but controls, error codes and homeowner reset procedures vary by model and manufacturer.