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HVAC Diagnostic Guide MEDIUM URGENCY

Heat Pump Running Constantly

Heat pump compressor running continuously without cycling off.

Quick Check Before You Call a Pro

  1. Outdoor temperature below 35°F? Continuous running is normal — heat pumps work harder in cold
  2. Check thermostat setpoint — set very high makes the unit run continuously to catch up
  3. Look at AUX HEAT indicator on thermostat — engaged for too long = problem
  4. Note electric bill — has it spiked dramatically? May indicate aux heat overuse

01 · Most Likely Causes (Ranked)

40%

Below Balance Point (Normal Cold-Weather Behavior)

What's happening

Below your system's balance point (usually 25-40°F), the heat pump may run continuously to keep up. This is NORMAL — it's the most efficient way to extract every bit of heat available from cold outdoor air.

How to check

Check outdoor temperature. Is it below 35°F? Is your thermostat staying near setpoint despite continuous run? If so, system is operating correctly given conditions.

How to fix

No fix needed. Continuous operation in extreme cold is by design. If you're uncomfortable with the energy use, you can supplement with auxiliary heat for the coldest days.

20%

Low Refrigerant Charge

What's happening

Reduced refrigerant lowers heat output, so the system runs longer trying to reach setpoint. Often paired with weak warm air at vents.

How to check

Feel air at vents — should be 90-100°F. If only 75-85°F even in moderate weather, capacity is reduced. Confirmed by tech with pressure gauges.

How to fix

Licensed tech finds leak, repairs, recharges to manufacturer spec.

15%

Aux Heat Always Running

What's happening

Auxiliary electric heat strips are engaging during normal heat pump operation when they shouldn't. Uses 2-3x more electricity than the heat pump alone — bills spike.

How to check

Thermostat shows AUX HEAT or EMERGENCY HEAT engaged constantly. Outdoor unit may not be running while indoor heating still happens.

How to fix

Diagnostic depends on cause: stuck sequencer relay, miswired thermostat, failed outdoor sensor, or aggressive thermostat setpoint. Tech investigation needed.

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12%

Undersized System

What's happening

Heat pump is too small for the heating load it needs to serve. Common in homes that added square footage, lost insulation, or have heat pumps from a previous milder climate.

How to check

Even in moderate weather (40-55°F outside), system struggles to reach setpoint. Heat pump runs all the time during mild winter weather.

How to fix

Manual J load calculation determines required capacity. Options: improve insulation/sealing to reduce load, supplement with mini-split for problem areas, or upgrade system size.

8%

Stuck Reversing Valve (Partial)

What's happening

Valve is leaking refrigerant past the seal, so the system loses some heating capacity. Heat pump runs longer to compensate.

How to check

Vent air temperature lower than expected. Heat pump can never quite catch up. Confirmed with refrigerant pressures by a tech.

How to fix

Reversing valve replacement. Labor-intensive (brazing required). $400-700 total typical.

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Heat StripsReversing Valves

02 · Frequently Asked Questions

Is it normal for a heat pump to run all the time?
In cold weather (below 35°F), yes — long run times are how heat pumps work efficiently in cold weather. In mild weather (45°F+), constant running indicates a problem: low refrigerant, sizing issue, or other inefficiency.
How long should a heat pump run per cycle?
In mild weather (50-60°F): 15-25 minute cycles. In moderate cold (35-45°F): 30-60 minutes. In extreme cold (below 25°F): may run continuously and supplement with aux heat. All these are normal patterns.
Why is my electric bill so high with a heat pump?
Most likely: aux heat is engaging too often. Aux heat uses 2-3x more electricity than the heat pump alone. Common causes: aggressive thermostat setpoint changes, failed outdoor sensor, or sequencer issue. A tech can diagnose.
Should I switch to emergency heat in cold weather?
No — emergency heat uses ONLY the electric resistance strips, completely bypassing the heat pump's efficiency. Always far more expensive. Only use emergency heat when the heat pump's outdoor unit is broken.

03 ·Related Symptoms

Heat Pump Not HeatingHeat Pump Auxiliary Heat Stuck OnHeat Pump Frozen Outside
⚠ Safety notice: This guide is for informational purposes only. HVAC systems involve high-voltage electricity, refrigerants under pressure, and natural gas — all of which can cause serious injury, death, or property damage. Refrigerant handling requires EPA Section 608 certification by federal law. When in doubt, contact a licensed HVAC professional.
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