If your heat pump is blowing cold air instead of warm air, you’re not alone. In Perth, where winters can dip below 10°C and summers spike past 40°C, a heat pump that’s not working right can turn your home from cozy to uncomfortable in minutes. Many people assume this means a costly repair or replacement-but often, the fix is simple. You don’t need to call a technician right away. Here’s what’s probably going on, and what you can do about it.
Check the Thermostat Settings
The most common reason a heat pump blows cold air? It’s not even set to heat mode. Sounds basic, but it happens more than you think. People switch between cooling and heating modes without realizing it. Check your thermostat display. Is it showing "Heat" or "Auto"? If it says "Cool," that’s your problem. Even if it says "Heat," make sure the set temperature is at least 2°C higher than the current room temperature. A thermostat set to 20°C when the room is already at 19°C won’t trigger the heat pump to kick in.Also, check if your thermostat is on "Fan" mode instead of "Auto." In "Fan" mode, the blower runs constantly, even when the heat pump isn’t actively heating. That means cold air from the ducts gets blown through your home, making it feel chilly. Switch it back to "Auto," and the fan will only run when the system is actually heating.
Dirty Air Filter
A clogged air filter is the silent killer of heat pump efficiency. If airflow is restricted, the system can’t move enough air over the heat exchanger. That causes the heat pump to overheat and shut off prematurely-or worse, it triggers a safety lock that forces it into defrost mode more often than normal. In defrost mode, your heat pump temporarily stops heating to melt ice off the outdoor coil. During that time, the indoor fan may blow cool air.Check your filter. If it looks gray, dusty, or you can’t see light through it, it’s time to replace it. Most filters need changing every 1-3 months, depending on pets, dust levels, and usage. In Perth’s dry, dusty climate, you might need to replace yours every 45 days. A clean filter improves airflow, reduces strain on the motor, and helps the system heat more effectively. Replacing it costs less than $20 and takes two minutes.
Outdoor Unit Is Frozen or Blocked
Your heat pump pulls heat from the outside air-even in winter. But if the outdoor unit is covered in ice, snow, leaves, or dirt, it can’t absorb enough heat. That’s why your indoor unit blows lukewarm or cold air. In late autumn and early winter, leaves, grass clippings, and dust build up around the unit. In colder snaps, frost forms on the coils. While heat pumps have a defrost cycle, heavy buildup can overwhelm it.Turn off the heat pump at the thermostat. Then, go outside. Clear away leaves, twigs, and debris. Use a garden hose (not a pressure washer) to gently rinse off the coils. Don’t chip ice with metal tools-that can damage the fins. If you see thick ice that doesn’t melt after an hour, the system might have a refrigerant leak or a faulty reversing valve. That’s when you need a pro.
Refrigerant Leak
Heat pumps use refrigerant to move heat from outside to inside. If there’s a leak, there’s not enough refrigerant to carry heat effectively. The system runs longer, but the air coming out stays cool. You won’t see a puddle or smell anything-refrigerant leaks are silent.Signs you have a leak: your heat pump runs constantly but never heats the house, ice forms on the copper lines near the outdoor unit, or your energy bills spike without a change in usage. Refrigerant isn’t something you top up like oil. It requires a licensed technician to find the leak, repair it, and recharge the system. If your unit is over 10 years old and needs a recharge, ask if replacement makes more sense. Newer models are 30-50% more efficient.
Defrost Cycle Is Running Too Often
Heat pumps naturally go into defrost mode every 30-90 minutes in cold, humid weather. This melts ice off the outdoor coil. During defrost, the system reverses briefly and blows cool air indoors. That’s normal. But if it’s happening every 10-15 minutes, something’s wrong.Common causes: dirty coils, low refrigerant, a faulty sensor, or a stuck reversing valve. If you notice your heat pump switching from heating to cooling every few minutes, and the air feels noticeably colder each time, it’s cycling too often. You can test this: turn the thermostat up to 26°C. If the defrost cycles don’t slow down, the system is malfunctioning. This isn’t a DIY fix. A technician will check the defrost control board and sensor readings.
Blower Motor or Ductwork Issues
Sometimes, the heat pump is working fine-but the air never reaches you. A failing blower motor might run too slow, pushing air at half speed. That means even warm air feels cool because it’s not moving fast enough. Or, your ducts might have leaks, especially if they run through unheated spaces like attics or underfloor cavities.Check your vents. Are they warm to the touch? If not, the air might not be getting hot enough. If they’re warm but airflow feels weak, the blower motor might be weakening. Dusty ducts can also reduce airflow. In older homes, ducts are often sealed with duct tape that dries out and cracks. Look for gaps near joints. You can temporarily fix small leaks with aluminum foil tape (not regular duct tape). But if you suspect major duct damage, a duct sealing service is worth the investment.
Age and Wear
Heat pumps last 10-15 years on average. If yours is 12+ years old and you’re having frequent issues, it’s likely wearing out. Older units use R-22 refrigerant, which is banned in Australia. Recharging them is expensive and becoming harder. Newer models use R-410A or R-32-both more efficient and eco-friendly.Signs your heat pump is at end-of-life: frequent repairs, strange noises (grinding, squealing), uneven heating across rooms, or high electricity bills. If you’ve spent more than $800 on repairs in the last year, replacement is usually cheaper in the long run. Modern heat pumps can cut heating costs by 40% and come with smart thermostats built in.
What to Do Next: A Simple Checklist
Here’s what to check in order, starting with the easiest:
- Is the thermostat set to "Heat" and the temperature higher than the room? Switch from "Fan" to "Auto."
- Replace the air filter if it’s dirty.
- Clear debris and ice from the outdoor unit. Rinse coils gently with water.
- Check if vents are warm. If not, the heat pump might not be producing heat.
- Listen for unusual noises or frequent on/off cycles.
- If none of the above work, call a licensed heat pump technician. Don’t try to recharge refrigerant yourself.
Most of these fixes take less than 30 minutes. You don’t need to spend hundreds before trying them. And if you’ve checked all these and the heat pump still blows cold air, it’s time for professional help. But at least now you’ll know what to tell them.
Why is my heat pump blowing cold air when it’s set to heat?
The most common reasons are the thermostat being set to "Cool" or "Fan," a dirty air filter, or the outdoor unit being frozen. The system might also be in defrost mode, which temporarily blows cool air to melt ice off the outdoor coils. If the issue persists after checking these, there may be a refrigerant leak or a faulty reversing valve.
Can I fix a refrigerant leak myself?
No. Refrigerant is a regulated substance and requires a licensed technician to handle. Attempting to recharge or repair a leak yourself is illegal in Australia and dangerous. Signs of a leak include ice on copper lines, constant running without heating, and rising electricity bills. A technician will locate the leak, repair it, and recharge the system properly.
How often should I replace the air filter in my heat pump?
In Perth’s dry, dusty climate, replace the air filter every 45 days if you have pets or allergies. Otherwise, every 60-90 days is typical. A dirty filter restricts airflow, causes the system to overheat, and forces it into defrost mode more often. Check the filter monthly-if you can’t see light through it, replace it.
Is it normal for my heat pump to blow cool air during defrost mode?
Yes. During defrost mode, the heat pump temporarily reverses to melt ice from the outdoor coil. This can last 5-15 minutes and may cause cool air to blow indoors. If it happens every 10-15 minutes, the system is cycling too often, which could indicate a dirty coil, low refrigerant, or a faulty sensor. Normal defrost cycles occur every 30-90 minutes in cold, humid weather.
When should I replace my heat pump instead of repairing it?
Replace your heat pump if it’s over 10 years old, you’ve spent more than $800 on repairs in the last year, or it uses R-22 refrigerant (banned in Australia). Newer models are 30-50% more efficient, quieter, and come with smart controls. If your unit struggles to keep up, has frequent breakdowns, or makes loud noises, replacement is usually the smarter long-term choice.