Heat pumps are known for their energy efficiency and reliability as heating and cooling systems. However, like any complex appliance, they can sometimes malfunction. One of the most common issues is constant restarting, also known as short cycling. This behaviour isn’t just annoying, it often indicates an underlying problem that can harm the system’s performance, increase electricity consumption, and cause premature wear on the compressor or other key components.
Understanding the potential causes of these interruptions is the first step in protecting the efficiency and longevity of your system. This guide offers a detailed analysis of the main reasons for abnormal start-stop cycles and provides concrete solutions.
Why Is Your Heat Pump Constantly Starting and Stopping?
A properly sized and functioning heat pump runs in regular cycles: it turns on when the indoor temperature drifts from the setpoint and turns off once the target is reached. However, when cycles become excessively short (every few minutes) this may indicate a more serious issue. It stresses mechanical components, increases energy costs, and reduces thermal comfort inside your home.
Possible causes include incorrect thermostat programming, worn temperature sensors, electrical irregularities, or an improperly sized system for your home’s size or insulation level.
Understanding the Normal Heat Pump Cycle
A normal cycle typically lasts 15 to 20 minutes, depending on weather conditions, insulation quality, and outdoor temperature. This intermittent operation is natural and aims to maintain indoor temperature without wasting energy.
When cycles become too short, the system doesn’t complete the thermal regulation process. This instability leads to higher energy use, poor dehumidification, and prevents the heat pump from operating within its optimal efficiency range, reducing its lifespan.
Faulty Sensors and Control Board Issues
Defective indoor or outdoor temperature sensors may give inaccurate readings to the control unit. If a sensor indicates it’s hotter or colder than it really is, the heat pump may turn on unnecessarily. Likewise, electronic problems in the control board or relays can disrupt the system’s logic.
Some models also include ambient temperature probes or pressure sensors that influence cycle duration. If these are miscalibrated or failing, erratic behaviour may occur.
Overheating: Causes and Fixes
If the unit overheats, the system will trigger a thermal protection shutdown to prevent permanent damage to the compressor. Causes of overheating may include:
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Insufficient airflow
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Faulty fan
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Dirty outdoor coils, which hinder heat exchange
Sometimes, excessive ambient temperature around the unit or poor clearance at vent openings can also lead to overheating. Preventive maintenance (including coil cleaning and airflow inspection) is essential to resolve this issue.
Blocked Ventilation Can Cause Overheating
A blocked or restricted ventilation system can lead to a quick rise in internal temperature, causing the unit to shut down as a safety measure. This includes:
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Dirty filters not replaced on time
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Air ducts partially obstructed by debris or furniture
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Closed or misaligned registers
Even dust or pet hair buildup in return vents can impair performance. You should inspect vents, ducts, and filters every 3 months to ensure optimal airflow.
Electrical Issues and Their Impact on Your Heat Pump
Unstable power supply or power surges may trigger the heat pump’s built-in protection system. A faulty start capacitor, oversensitive breaker, or poor grounding can also cause premature restarts.
In older homes, the electrical system may not meet modern HVAC demands. A complete electrical inspection is advisable if you experience frequent shutdowns or restarts without thermostat changes.
Heat Pump Maintenance for Optimal Performance
Regular maintenance is essential for performance and system longevity. This includes:
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Cleaning filters every 3 months
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Inspecting condenser coils
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Cleaning condensate drains
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Checking refrigerant pressure
Annual professional servicing can identify weakened parts before they cause serious issues. Poor maintenance is one of the main causes of recurrent short cycling in wall-mounted systems.
Short Cycling and Increased Energy Consumption
Each restart consumes more energy than steady operation. Repeated power surges increase your energy bills without improving comfort.
The compressor and fans work harder at every startup, wearing out faster. A more stable system uses less energy and delivers better seasonal performance.
Thermostat Settings: How to Adjust Them Properly
An overly sensitive or poorly calibrated thermostat can cause frequent changes. To avoid this:
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Set a stable temperature range
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Use eco mode or smart mode for better regulation
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Avoid constant manual changes
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Limit temperature swings between day and night to 2–3°C max
Modern thermostats with occupancy sensors or geolocation features can optimize performance and reduce unnecessary cycling.
Air Filter Cleaning and Replacement
Dirty filters are a major cause of overheating and short cycling. They restrict airflow, force the compressor to work harder, and disrupt heating/cooling cycles.
Recommendations:
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Check filters every 30–60 days
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Use MERV 11+ filters if you have pets or allergies
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Replace, don’t just clean, filters in dusty environments
Proper Sizing: Choosing the Right Heat Pump
An oversized unit heats or cools the space too quickly, leading to short cycles. An undersized unit runs constantly without reaching the setpoint, reducing overall efficiency.
Proper sizing depends on:
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Living area size
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Home orientation
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Insulation level
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Number of thermal zones
A professional thermal load calculation is essential before installation.
When to Call a Professional
Call a certified technician if you notice:
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Restarts every 3–5 minutes
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Unstable indoor temperature
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Unusual noises during startup
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Higher-than-normal electricity bills
A professional evaluation not only resolves existing issues but can also prevent future breakdowns.
Conclusion: Towards a More Stable and Durable Heat Pump
An unstable heat pump is a warning sign. Short cycling should not be ignored; it reduces system performance, increases energy costs, and shortens lifespan. By identifying the cause, performing regular maintenance, and consulting a qualified professional, you can restore stable thermal comfort and protect your investment.
Thinking about getting your system inspected or replaced? Choose a brand known for reliability and performance. Daikin heat pumps are designed to deliver consistent output and stable operation, even in Quebec’s harshest weather.
Contact a certified Daikin installer for a personalized system assessment and enjoy year-round peace of mind.
