Heat pumps are one of the most efficient ways to heat and cool your home, especially in places like Perth where summers are hot and winters are mild. But even the best systems can break down - and when they do, there’s usually one problem that shows up over and over again: the heat pump not heating.
You turn on the thermostat, the fan runs, but cold air blows out. You check the filter - it’s clean. You reset the breaker - no change. You stare at the outdoor unit and wonder why it’s not pulling heat from the air like it should. This isn’t a rare glitch. In fact, over 60% of heat pump repair calls in Western Australia are for this exact issue.
Why Your Heat Pump Stops Heating
The most common reason your heat pump won’t heat is a refrigerant leak. Heat pumps move heat using refrigerant - a chemical that absorbs heat from outside air and releases it inside. If the refrigerant level drops too low, the system can’t transfer enough heat. That’s why you get lukewarm air instead of comfortable warmth.
Leaks happen slowly. You won’t notice them until the system starts struggling in winter. Small holes in copper lines, worn valves, or loose fittings are the usual suspects. Older units, especially those over 10 years old, are more prone to this. In Perth’s dry climate, corrosion from dust and salt air can eat away at outdoor coils over time.
Another big culprit? A dirty outdoor coil. People think the filter is the only part that needs cleaning. But the outdoor unit - the one sitting in your yard - collects leaves, pollen, and dust. When it gets clogged, airflow drops. The system can’t absorb enough heat from the air, even if the refrigerant is fine. I’ve seen units that looked like they’d been buried under a pile of gum leaves. After a simple cleaning, the heat came back.
Defrost Mode Gone Wrong
Heat pumps work by pulling heat from cold air. But when temperatures dip below 5°C, frost starts forming on the outdoor coil. That’s normal. The system has a defrost cycle that melts it off automatically.
But if the defrost sensor is faulty, or the control board is glitching, the system gets stuck in defrost mode. Instead of heating your home, it spends half the time melting ice and the other half doing nothing. You’ll notice the indoor unit blowing cool air, and the outdoor unit might even be steaming - but the house stays chilly.
This is especially common in older models with analog thermostats. Modern heat pumps use smart sensors that adjust based on humidity and temperature. If your unit is from before 2015, this could be the hidden problem.
Thermostat Misunderstandings
It sounds simple, but a lot of people blame the heat pump when the real issue is the thermostat. You set it to 22°C, but the system never reaches it. Why? Because it’s on “cool” mode. Or “emergency heat” is turned on by accident. Or the batteries are dead.
Some thermostats have a switch labeled “Heat/Cool/Auto.” If it’s on “Cool,” your heat pump will never heat. Others have a separate “Emergency Heat” button - meant for backup use only. If you leave it on, the system runs on electric resistance heating, which uses way more power and doesn’t feel as warm.
Check the display. Is it showing “Heat” or “Cool”? If it’s blank, replace the batteries. If it’s showing an error code like “E1” or “LO,” that’s a sign the thermostat needs replacing - not the whole heat pump.
Blower Motor and Airflow Issues
If the air coming out of your vents is weak, the problem might not be the heat pump itself. It could be the blower motor. This motor pushes air through your ducts. If it’s worn out, clogged with dust, or the capacitor is dead, airflow drops. Less airflow means less heat reaches your rooms.
Signs of a failing blower motor:
- A loud grinding or squealing noise when the system turns on
- Warm air that doesn’t feel strong
- The unit runs constantly but never heats the house
Replacing the capacitor is cheap - under $50. Replacing the whole motor can cost $500-$800. But if you don’t fix it, the strain can damage the compressor, which is a $2,000+ repair.
When It’s Not the Heat Pump
Before you call a technician, check these simple things:
- Is the power switch on? Some units have a separate on/off switch near the outdoor unit.
- Are the vents open? Closed vents reduce airflow and make the system work harder.
- Is the outdoor unit blocked? Snow, dirt, or even a potted plant can restrict airflow.
- Did you change the filter? Even if it looks clean, a clogged filter reduces efficiency by 15-30%.
One homeowner in Canning Vale thought his heat pump was broken. He called three technicians. Turns out, his curtains were drawn shut all day. The heat from the unit was trapped in the ceiling, and the cold air from the floor vents never reached him. He opened the curtains, and the problem disappeared.
Preventing the Problem Before It Starts
Heat pumps last 15-20 years if maintained. But most people wait until winter hits to check them. That’s too late.
Here’s what you should do twice a year - in late spring and early autumn:
- Turn off the power and clean the outdoor coil with a garden hose (don’t use a pressure washer).
- Replace the air filter - even if it looks clean. Dust builds up inside.
- Check for ice or frost on the outdoor unit in winter. If it’s thick, let the system defrost. Don’t chip at it.
- Set your thermostat to “Heat” mode and confirm it’s not on “Emergency.”
Keep a log. Note when the system starts acting up. Did it happen after a storm? After a filter change? Patterns help technicians diagnose faster.
What to Do When It Breaks
If you’ve checked everything and the heat pump still won’t heat:
- Don’t keep turning it on and off. That strains the compressor.
- Use space heaters temporarily - but only if they’re certified and kept away from curtains.
- Call a licensed HVAC technician. Ask if they have a refrigerant leak detector. Not all do.
- Get a quote before any repairs. If the unit is over 12 years old and needs a new compressor, replacement is often cheaper.
Heat pump repairs aren’t cheap. A refrigerant recharge costs $200-$400. A new outdoor coil? $1,200+. But ignoring the problem can cost you more - higher bills, a blown compressor, or a system that dies in the middle of winter.
The most common problem with heat pumps isn’t a mystery. It’s usually something simple - a leak, a dirty coil, or a thermostat stuck in the wrong mode. Fix it early, and you’ll save money, time, and a lot of cold mornings.
Why does my heat pump blow cold air in heating mode?
If your heat pump blows cold air while set to heat, it’s likely low on refrigerant, the outdoor coil is clogged, or it’s stuck in defrost mode. A dirty air filter or a faulty thermostat can also cause this. Start by checking the thermostat setting and replacing the filter. If the problem continues, call a technician to check refrigerant levels and coil condition.
How often should I clean my heat pump’s outdoor unit?
Clean the outdoor unit at least twice a year - once in spring and once in autumn. In dusty or coastal areas like Perth, clean it every 3 months during high-pollen seasons. Turn off the power, then gently spray the coil with a garden hose. Never use a pressure washer - it can bend the fins and damage the unit.
Is it normal for my heat pump to frost up in winter?
A light layer of frost is normal when temperatures drop below 5°C. The heat pump has a built-in defrost cycle that melts it off automatically. If the frost builds up thicker than a few millimeters, or if the unit stays frozen for hours, the defrost sensor or control board may be faulty. In that case, the system won’t heat properly until it’s repaired.
Can I recharge the refrigerant myself?
No. Refrigerant is a regulated substance and requires special equipment and licensing to handle. Trying to recharge it yourself can lead to leaks, environmental damage, or injury. Always hire a licensed HVAC technician. They’ll find the source of the leak first, fix it, then properly recharge the system.
When should I replace my heat pump instead of repairing it?
Consider replacement if your heat pump is over 12 years old, needs a compressor repair, or if the cost of repairs exceeds 50% of a new unit’s price. New models are up to 40% more efficient and come with better warranties. If you’re paying high electricity bills or the system runs constantly just to keep up, it’s time to upgrade.