Air-to-water heat pumps are designed to provide energy-efficient, reliable heating year-round. However, when your system isn’t delivering enough warmth during cold months, it can be frustrating and costly. If you’re wondering, “Why is my heat pump not heating properly?”, you’re not alone. In this article, we break down the most common reasons for poor heating performance, how to diagnose them, and what you can do to resolve the issue.

1. Incorrect Thermostat Settings

One of the most common causes of heating issues is simply a misconfigured thermostat.

✅ How to Fix:

• Ensure the thermostat is set to “HEAT” mode.

• Verify that the target temperature is higher than the current room temperature.

• If you’re using a smart thermostat, check for schedule overrides or eco settings that may be limiting performance.

2. Clogged Air Filters or Dirty Coils

Dust and debris buildup can reduce airflow and heat exchange efficiency, causing poor heating performance.

✅ How to Fix:

• Clean or replace air filters monthly.

• Inspect indoor and outdoor coils for dirt or frost, and clean them gently with a soft brush or water spray.

❄️ 3. Defrost Mode Issues

During winter, outdoor units periodically switch to defrost mode to prevent coil freezing. If the system is stuck in defrost or performs it too frequently, it will reduce heating capacity.

✅ How to Fix:

• Observe if the outdoor unit is frequently icing over.

• Ensure proper drainage around the unit.

• Contact a technician if defrost cycles are excessively long or ineffective.

4. Low Refrigerant Levels

If refrigerant leaks occur, your heat pump won’t transfer enough heat to warm your home.

✅ How to Fix:

• Check for hissing sounds or visible frost on refrigerant lines.

• Only certified HVAC professionals should test, locate, and recharge refrigerant safely.

5. Outdoor Temperature Too Low for Standard Mode

Air-source heat pumps become less efficient in extremely cold climates (typically below -10°C/14°F).

✅ How to Fix:

• Upgrade to a cold-climate heat pump model.

• Supplement with a backup boiler or integrated heating system.

⚙️ 6. Poor System Sizing or Design

A heat pump that’s too small for your property’s heating load will constantly struggle to meet demand.

✅ How to Fix:

• Request a professional heat load calculation (Manual J) to assess if your system is properly sized.

• Consider a zoned system or upgrading to a larger-capacity heat pump.

7. Faulty Sensors or Controls

Malfunctioning sensors may incorrectly read room or water temperatures, causing improper heating cycles.

✅ How to Fix:

• Check for error codes on your control panel.

• Have a technician test temperature probes and control boards.

8. Airlocks or Circulation Issues

For air-to-water systems, if water isn’t circulating properly due to airlocks, valve issues, or pump failure, the system won’t heat effectively.

✅ How to Fix:

• Bleed radiators or underfloor circuits to remove trapped air.

• Inspect the circulation pump for operation and sound.

• Ensure all motorized valves are open and functioning.

9. System Needs Regular Maintenance

Annual servicing is essential to keep your heat pump running efficiently. A neglected unit will degrade in performance over time.

✅ Maintenance Checklist:

• Clean filters and coils

• Inspect electrical connections

• Test refrigerant levels and flow rates

• Flush heat exchangers if needed

When to Call a Professional

If your heat pump:

• Struggles to reach set temperatures

• Shows persistent error codes

• Ices up frequently or leaks water
  …then it’s time to call a qualified HVAC technician for a full system inspection.

✅ Conclusion

A heat pump not heating properly can result from simple fixes like filter cleaning or thermostat settings, or from more complex issues like refrigerant leaks and undersized systems. Regular maintenance, smart system design, and prompt professional support can ensure optimal performance, energy efficiency, and long-term reliability.