Heat pumps are designed to run long cycles to minimize system wear and tear while maintaining a consistent temperature. However, they should not operate constantly.
If your heat pump is running tirelessly, hour after hour, it might indicate an issue with your HVAC system, so keep reading to learn more.
At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.
The Two Scenarios that a Heat Pump Can Run Continuously
There are two situations where a heat pump that runs continuously is not considered a good sign:
- When the heat pump keeps running after attaining the desired setpoint temperature
- When the heat pump keeps trying to reach the setpoint for hours (and failing to do so)
Below, I’ll show you troubleshooting steps for both scenarios, starting with the first one: a stubborn heat pump that doesn’t shut down, even after reaching the desired temperature.
Scenario 1: Heat Pump That Continues to Run, After Reaching the Set Temperature
If your heat pump continues to run after reaching the set temperature, it may be due to a malfunctioning thermostat, incorrect temperature calibration, or a weak capacitor, requiring professional diagnosis and repairs.
So let’s go through these, step-by-step.
1. The Blower Fan is Set to “On”
It's possible that it's not actually the heat pump that is continually running after the set temperature is reached. It may be the blower fan within the air handler that continues to run, sending air through the ducts 24/7.
You can check the fan setting on your thermostat. If set to “On” it means the blower is running constantly. While in “Auto” it will stop when the heat pump stops.
A fan/blower that's running non-stop can help circulate air more frequently throughout the house. However, it can wear down the system faster and in some cases, prevent the air conditioner from reducing the moisture in your home.
Solution: Set your blower fan setting to “Auto” as it's more economical and prevents the fan from overheating.
2. Thermostat Wiring is Loose
Inspecting the thermostat wiring is essential because loose or damaged wires can prevent the shutoff signal from properly reaching your heat pump, causing it to run continuously.
- First, disconnect the power to your thermostat.
- Then, remove the thermostat from its wall mount to examine the wire strip for any loose connections or damage.
- If necessary, reconnect the cables tightly and ensure the wires are attached to the appropriate terminals.
This simple inspection can help restore your thermostat's ability to communicate effectively with your heat pump and prevent constant running.
3. Thermostat Batteries Might be Dying Out
Some thermostats, without a C-Wire, are powered by AA or AAA batteries. When those batteries run low, there may not be enough power to call the heating system to deactivate.
Solution: In this scenario, it is best to replace the batteries.
4. The Heat Pump Might Be Auto-Switching from Heat to Cool to Maintain the Temperature
Heat pumps or thermostats with an auto-reverse, or auto-changeover function, can enable the system to seamlessly transition between heating and cooling modes.
This function can help automatically maintain the desired setpoint without you having to manually switch back and forth between heating and cooling.
If your heat pump runs even after reaching the set temperature, it might be because it's distributing cool air to maintain this set point.
Usually, there’s a “Deadband” or “differential” temperature range (of about 0.5°F-1.0°F from the setpoint) where the heat pump stops working.
In this scenario, the thermostat might have breezed through this temperature point or this setting might have been disabled or altered in your thermostat’s installer settings.
Solution: To safely rule this out,
- First, deactivate the “Auto” temperature mode
- Set the system to either heating or cooling mode
- Increase (for heating) or decrease (for cooling) the setpoint temperature by a small amount (probably by 2°F or 5°F),
- Monitor the heat pump until the thermostat reaches this desired setpoint and turns off by itself.
If the heat pump turns off, and the thermostat doesn’t whizz past this desired setpoint, you can be sure that it’s the auto-switching function that’s causing the heat pump to run continuously.
In that case, try adjusting this differential value or improving your home’s insulation. On top of that, confirm the temperature sensor of the thermostat is reading correctly by comparing it with a separate thermometer.
5. Blower Relay Switch Might Be Stuck or Malfunctioning
Due to a stuck blower relay, the signals from the thermostat might not be going through, causing the blower to continue running even after the heat pump has been turned off.
While it's possible to replace the relay yourself I recommend hiring a professional to avoid damaging the equipment (or yourself!).
Solution: Try switching off the fan or setting it to “Auto” and seeing if the blower dies down, if not, check the blower relay or get it looked at by a professional.
The blower motor relay is typically found inside the furnace or air handler, which can be either an indoor or outdoor unit, depending on your system setup.
6. The EM Heat Setting Might Be Turned On
It may be possible the emergency heat setting has been activated on your thermostat.
The Emergency heat setting disables the primary heat pump and attempts to switch on the emergency heating system. This could be coupled with another issue, such as a failing defrost cycle, causing the system to glitch into running the heat pump indefinitely.
Solution: Make sure the Emergency heat setting is manually turned off, or if there are any indications that the auxiliary heating system (the backup heat option that automatically activates) is engaged.
If you don’t find any indication of the backup heat settings, you can:
- Change the system to “heat”
- Lower the temperature to “force” the thermostat to attain its desired setpoint
- Check if the thermostat automatically shuts down the heat pump.
If the heat pump doesn’t shut down after that, it might be malfunctioning, so it’s best to call in a professional.
Scenario 2: Heat Pump Continues to Run, Without Reaching the Set Temperature
If your heat pump constantly runs without ever hitting the target temperature, there could be underlying issues such as leaky ducts, low refrigerant, or a malfunctioning thermostat, which needs proper diagnosis and repair.
So let’s start troubleshooting this issue.
1. Faulty Temperature Sensor
In some cases, your thermostat might be engaging the heat pump non-stop because it’s reading the temperature in your home incorrectly.
Faulty temperature sensors are rare but if the thermostat placement is not ideal, it could cause the thermostat to measure temperatures incorrectly.
Solution: Compare temperatures using a separate thermometer and move or replace the thermostat accordingly.
2. Clogged Air Filter or Snow Drift on Outdoor Unit
A clogged air filter or snow drift on the outdoor unit can disrupt the heat pump. On top of that, if the indoor or outdoor filters become obstructed, the heat pump struggles with airflow, forcing it to work harder to reach the desired temperature.
In extreme cases, the heat pump may never hit the target temperature, causing it to run non-stop.
- Check and clean the outdoor unit to ensure it is free of obstructions, such as snow or debris.
- Next, replace the indoor air filter to improve airflow and overall performance.
- After that, setup reminders so you don’t forget to replace the indoor air filters monthly, bi-monthly, or every three months (depending on the filter’s specifications).
3. System Lacks an Auxiliary Heat Source and the Temperature Setpoint is Too High During Cold Weather
When dealing with cold weather, it's important to understand that your heat pump's efficiency decreases as the outside temperature drops below 30º F (-1º C).
If you set your thermostat to an extremely high-temperature setpoint, such as 80 °F (27º C), your heat pump may struggle to achieve this goal, causing it to run continuously.
This is due to the limited heat output capacity at low outdoor temperatures.
- To avoid constant running, consider lowering your thermostat's temperature setting or using an auxiliary heat source.
- Some thermostats offer the option to activate auxiliary heating when the heat pump runs incessantly for a set period of time. If this feature is not enabled, you can either set it up yourself through the installer settings or consult a professional.
4. Temperature Set Too Low During Hot Weather
Conversely, during hot weather, setting the heat pump's temperature too low can cause it to run constantly as it struggles to lower the indoor temperature to an unattainable level.
In some cases, the cooling system may be undersized, the outdoor temperature could be excessively high, or your home's insulation might not be adequate.
- Try adjusting the setpoint temperature to a more achievable level, and verify if the heat pump's cooling system can reach this temperature and shut down on its own.
- Also, ensure that the thermostat's temperature mode is set to “Cool” rather than “Auto.”
5. Windows / Doors Open or Poor Insulation
If your home has open windows or doors, drafts can cause warm air to escape, making it difficult to maintain a consistent temperature.
- To solve this, close all windows and doors and check again
- Consider upgrading your home's insulation for better energy efficiency.
- Get help from an HVAC service to check for under-insulation.
6. Refrigerant Leak
A refrigerant leak could cause your heat pump to never stop running, trying to pump in warm air that’s not warm enough to meet the desired temperature.
Although you can’t confirm a leak very easily, you can identify certain signs such as:
- Cold air blowing in from the vents when you’ve set the thermostat to “heat”
- Hissing sounds near the coils and compressor
- Oily residue or condensate at the base of the indoor/outdoor units
- Get help from an HVAC technician to identify the leak
- Top up if the leak is not very significant.
- If the leak is too big, or located in a higher-pressure area, you might have to replace certain parts.
7. Damaged Compressor Contactor
A damaged compressor contactor could be stuck or malfunctioning due to various issues, causing your heat pump to run continuously.
Solution: Inspect the contactor yourself and replace it if needed, or seek assistance from a professional.
8. Malfunctioning or Unplugged Condensate Pump
A heat pump in cooling mode generates water as a natural byproduct of the air conditioning process.
This water typically drains into a floor drain or is collected and removed by a condensate pump through a discharge tube.
The constant running of your heat pump might be due to a malfunctioning or unplugged condensate pump.
- To troubleshoot this issue, first, ensure the condensate pump is plugged in. Make sure you're plugging it into a GFCI outlet or a wall outlet that's got residual current protection.
- Next, clean the reservoir, intake vents, and float switches, making sure to turn the power off when adding water. The condensate pump and its reservoir are located next to the indoor unit of your furnace, heat pump, or air handler.
- Check that the float switches can move freely and click during on/off positions.
- Fill the reservoir with water to see if the pump can drain it successfully.
- If not, remove the check valve and observe if water flows out from the check valve's outlet when powered on, don’t forget to place a container beneath the reservoir to catch excess water.
- If water doesn't flow out, the pump may be defective, and a replacement might be necessary.
- Otherwise, clean the check valve's insides with a Q-tip or paperclip, reinstall it, and test again.
- If the pump still fails to push water out through the check valve, consider replacing the check valve itself.
9. Failed Defrost Cycle
This happens when the outdoor unit's coil becomes covered in ice and the defrost cycle fails to efficiently thaw it out.
In such cases, the heat pump's defroster may have a problem, such as a malfunctioning timer or temperature sensor.
If your outdoor coil has a significant ice build-up, it's a good indication that the defrost cycle isn't working properly.
- Start by visually inspecting the outdoor coils for excessive ice build-up.
- If they appear frozen try resetting the system
- If that doesn't seem to work, enlist the help from a professional HVAC technician.
An HVAC technician can diagnose the issue, repair or replace any faulty components, and ensure that your heat pump's defrost cycle is functioning as it should, preventing further ice accumulation and improving your system's efficiency.
10. Stuck Reversing Valve
Heat pumps contain reversing valves to switch between heating and cooling. If one of these valves gets stuck, the heat pump will continually run in this stage, never reaching its temperature or sometimes creating the opposite effect.
Solution: Check air coming through vents to see if it is cold when the thermostat is set to high. If so, arrange an inspection and service
10. Undersized Heat Pump or Ductwork
An undersized heat pump or duct setup can struggle to efficiently maintain the desired temperature in a large home, causing it to run constantly without ever reaching the set point.
- Compare the heat pump's specifications to your home's square footage
- Or, have a professional HVAC company perform a heat load calculation.
- This assessment will help determine whether your current system is adequate or if an upgrade is necessary for optimal performance.
A heat pump that’s constantly running is not a good sign as it can put extra strain on the system and cause the filter and heating components to wear down faster.
Most of the time, the heat pump might be running continuously because of the wrong signals provided by the thermostat but could also be due to stuck contactors, refrigerant leaks, and under-insulation.
In any case, it’s best to troubleshoot safely according to the guide above and get help from a professional if you hit a wall during this process.