Aurora, CO Heat Pump Not Cooling? 5 Common Causes

Estimated Read Time: 9 minutes

When a heat pump not cooling ruins your summer comfort, the cause is usually simple and solvable. In Denver’s fast-changing weather, a few small issues can shut down your cooling. This guide explains the five most common reasons your heat pump stops cooling, what you can safely check, and when to call a pro. If your system is aging, we also cover repair vs replacement and a limited-time rebate.

Start Here: Safe DIY Checks Before You Call

Before you worry about major repairs, confirm the basics. These simple checks solve many no-cooling calls in minutes.

1. Thermostat settings
2. • Set to Cool, not Heat or Auto.
   • Fan set to Auto. On can make air feel warm if the compressor is off.
   • Target temperature at least 3 degrees below room temperature.
2. Breakers and disconnects
3. • Check the outdoor unit’s breaker in the main panel and the service disconnect near the condenser.
3. Filters
4. • Replace a clogged filter if you cannot see light through it. A dirty filter can stop cooling and cause icing.
4. Vents and returns
5. • Open at least 80% of supply registers. Clear furniture and rugs from returns.
5. Outdoor clearance
6. • Clear leaves and cottonwood fluff within 2 feet around the outdoor unit.

If the system still does not cool after these steps, one of the reasons below is likely at play. Denver’s elevation can reduce system capacity, so small issues show up faster on hot afternoons along the Front Range.

Reason 1: Thermostat or Control Issues

Modern heat pumps rely on accurate thermostat signals. Wrong mode, dead batteries, or miswired controls can stop cooling.

What happens

• The thermostat commands the air handler fan but not the outdoor unit.
• Incorrect heat pump settings cause the reversing valve to stay in heating mode.
• Smart thermostats lose Wi-Fi or glitch after updates.

What you can check

• Replace batteries. Reboot the thermostat by removing it from the base for 30 seconds.
• Confirm heat pump equipment type in the thermostat’s setup. Many models have a dedicated heat pump configuration.
• Verify the thermostat is level and not in direct sun that can skew readings.

Why call a pro

• Heat pump wiring has specific terminals for the reversing valve. Miswiring can lock the system in the wrong mode.
• A failed control board can mimic a thermostat problem.

Bell’s diagnostic approach includes meter testing of low-voltage circuits, board fault codes, and verification that the reversing valve energizes in the correct mode for your brand.

Reason 2: Dirty Filters and Coils Starve Airflow

Airflow is the lifeblood of a heat pump. If your filter or coils are dirty, the evaporator coil can ice over and cooling stops.

Symptoms to watch for

• Weak airflow at vents.
• Ice on the refrigerant lines or outdoor unit.
• Short cooling cycles with long fan run times.

DIY steps

• Replace the filter. Use the MERV rating your system allows. Too high can restrict airflow.
• Let ice melt fully before restarting. Turn the system Off at the thermostat and set the fan to On for 30 to 60 minutes.

Professional fixes

• Coil cleaning with manufacturer-approved chemicals.
• Blower wheel cleaning and static pressure testing.
• Duct balancing to restore designed airflow.

Why it matters in Denver

• Cottonwood season fills outdoor coils fast. High-altitude, dry air already pushes systems on 95-degree days, so even minor blockage costs capacity.

Reason 3: Low Refrigerant or a Leak

A heat pump that runs but never cools often has low refrigerant. Refrigerant is not a fuel. If it is low, you have a leak.

Common signs

• Longer run times with lukewarm supply air.
• Hissing at the indoor coil or oil stains on lines.
• Frozen indoor coil or outdoor frosting in mild weather.

What not to do

• Do not top off refrigerant without leak detection. This wastes money and can damage the compressor.

What a pro will do

• Perform electronic and bubble leak tests on common failure points like flare fittings and coil u-bends.
• Recover, weigh, and recharge to factory spec. Charging by guesswork leads to poor performance and high bills.
• Repair options include tightening flares, replacing Schrader cores, or fixing coils if feasible.

When replacement makes sense

• If the repair costs more than half of a new heat pump or the system uses obsolete refrigerant, a replacement can save energy and reduce future repair risk. Bell installs high-efficiency Rheem and Mitsubishi heat pumps sized for Denver homes.

Reason 4: Outdoor Unit Problems and Obstructions

Your outdoor unit rejects heat. If it cannot breathe, your home will not cool.

Likely causes

• Cottonwood, grass clippings, or pet hair blocking the coil.
• Damaged condenser fan or failed fan motor.
• Outdoor unit placed in a corner without adequate clearance.

Homeowner checks

• Shut power off and gently hose the coil from inside out if accessible. Do not bend fins.
• Maintain 2 feet of clearance around all sides and 5 feet above.

Professional solutions

• Deep coil cleaning and fin straightening.
• Motor capacitor testing and replacement.
• Recommendations for wind or snow barriers that do not restrict airflow. In winter, heat pumps can frost. Your defrost cycle should clear it. If it does not, a sensor may be failing.

Reason 5: Duct Leaks, Sizing, or Installation Errors

If the system never cooled well, the issue may be design, not parts.

What we see around Denver

• Oversized equipment that short cycles and never dehumidifies.
• Leaky return ducts in basements or attics that pull in hot, dusty air.
• Inadequate supply runs to second floors in older homes.

How we fix it

• Load calculation and airflow audit using ACCA Manual J and static pressure testing.
• Seal and insulate ducts, especially in garages and crawlspaces.
• Right-size equipment and tune charge and airflow to spec.

Result

• Even cooling room to room, lower bills, and a quieter system. A well-designed heat pump should run steady on hot afternoons without constant cycling.

Repair or Replace: How to Decide

Use these common guidelines to protect your budget.

Repair may be best when

1. The unit is under 10 years old and maintenance has been consistent.
2. Repairs are minor, like a capacitor, contactor, or thermostat.
3. The system cools well once the specific fault is fixed.

Consider replacement when

1. Repairs are frequent and costly or involve major components.
2. Energy bills keep rising even after repairs and maintenance.
3. Your system is poorly sized or uses outdated refrigerant.

Bell’s difference

• Dependable Service Since 1926 is not just a tagline. Our NATE-certified team measures your home’s load, evaluates ductwork, and recommends the right technology, including variable-speed options that excel in Denver’s dry climate. We also install high-efficiency heat pumps from leading brands and verify performance on day one.

What Our Diagnostic Visit Includes

A precise diagnosis saves money and prevents repeat breakdowns.

Our technicians will

1. Verify thermostat and control board operations.
2. Inspect filters, blower, and indoor coil condition.
3. Test capacitors, contactors, and condenser fan motor.
4. Measure static pressure and temperature split.
5. Perform leak detection if pressures suggest a refrigerant issue.
6. Confirm the reversing valve and defrost controls operate correctly.

You receive

• A clear, upfront estimate with flat-rate pricing after we assess your system in person. We never quote blindly.
• Options for repair, maintenance, or replacement, including financing and rebate guidance for qualifying heat pumps.

Preventive Maintenance Pays Off

Prevent problems and keep comfort steady by enrolling in routine maintenance. Our team ensures your heat pump is ready when temperatures swing.

Routine maintenance offers several advantages:

• Increased energy efficiency, lowering your energy costs
• Longer lifespan for your heat pump with less frequent replacements
• Enhanced safety
• Fewer repairs over time, saving you money
• Improved comfort with a reliable heating system

What your visit includes

• Full system cleaning, electrical checks, and refrigerant performance testing.
• Airflow verification and duct inspection.
• Honest recommendations. If we find an issue, we handle repairs quickly.

Local Insight: Cooling in Denver’s Climate

Denver’s 5,280-foot elevation and dry air change how heat pumps behave. Afternoon highs can spike quickly, then drop at night. A properly sized, variable-speed heat pump will run longer and steadier, which is normal and more efficient. Cottonwood season requires outdoor coil cleaning. Hail protection matters too. Ask about low-restriction guards that protect coils without blocking airflow.

Hard facts that protect your investment

• Bell has served Denver since 1926 with a 100% Satisfaction Guarantee.
• Our technicians carry NATE certification and install high-efficiency systems from brands like Rheem and Mitsubishi.
• A current rebate can save eligible homeowners $2,200 on qualifying heat pumps. Call for details and eligibility.

Special Offer: Save $2,200 on a Qualifying Heat Pump

Upgrade your comfort and efficiency. Purchase a qualifying heat pump and receive a $2,200 rebate. Book online or call for rebate details. Offer available through 11/05/2025. Terms apply.

Call (720) 740-0350 or visit https://bellplumbing.com/ to schedule your free estimate.

What Homeowners Are Saying

"Enrique and Axel just finished installing our new heat pump! They were great! Super efficient and clean... They made our full furnace and air conditioner replacement easy... they were able to rearrange some appts so that they could give us heat in 24 hrs!"
–Tom T., Heat Pump Install

"Bell installed a heat pump style hot water heater. We were very pleased with their services - professional, timely."
–Jonathan F., Heat Pump Water Heater

"We had an issue with our HVAC water heat pump. Rich the technician arrived within the timing window, diagnosed our problem, walked us through the issues, and fixed the problem. Very professional."
–Jon R., Heat Pump Repair

"A mechanical engineer, Kyle knows his stuff. I wanted a heat pump water heater, and they accommodated my request... They did a workmanlike job. I would so use Bell again."
–Melissa B., Heat Pump Water Heater

Frequently Asked Questions

Why is my heat pump running but not cooling?

This usually points to a thermostat setting, dirty filter, or low refrigerant. Start by setting the thermostat to Cool, replacing the filter, and clearing debris around the outdoor unit. If cooling does not return, a professional diagnosis is needed.

Is it normal for my heat pump to ice up in summer?

No. Ice in cooling mode often signals airflow problems or a refrigerant issue. Turn the system off, set the fan to On to melt ice, replace the filter, and call a technician to check charge, coils, and airflow settings.

How often should I service my heat pump in Denver?

At least once before summer and once before winter if the system heats and cools. Denver’s cottonwood and dust load make coil cleaning and airflow checks important. Regular maintenance reduces repairs and improves efficiency.

Should I repair or replace my heat pump?

Repair if the unit is younger, well maintained, and the fix is minor. Consider replacement if repairs are frequent, the system uses outdated refrigerant, or major parts fail. If a repair costs more than half of a new unit, replacement often wins.

What temperature should I set for efficient cooling?

Most homes do well at 75 to 78 degrees with the fan on Auto. Use a 2 to 3 degree setback when away. Avoid large swings that force long recovery times during hot Denver afternoons.

Bottom Line

A heat pump not cooling usually comes down to controls, airflow, refrigerant, outdoor restrictions, or design issues. In Denver, small problems show up fast in dry, high-altitude heat. We diagnose precisely, fix quickly, and stand behind the work.

Ready to Get Comfortable Again?

Call (720) 740-0350 or schedule at https://bellplumbing.com/. Ask about the $2,200 rebate on qualifying heat pumps before 11/05/2025. Book now for fast service and a 100% Satisfaction Guarantee.

Call now: (720) 740-0350 • Book online: https://bellplumbing.com/ • Limited-time $2,200 heat pump rebate available on qualifying systems. Terms apply.

About Bell Plumbing, Heating, Cooling & Electrical

Since 1926, Bell has served the Greater Denver Metro with licensed, NATE-certified technicians and a 100% Satisfaction Guarantee. Homeowners choose us for flat-rate pricing, same-day service, and careful workmanship. We install and service high-efficiency systems from brands like Rheem and Mitsubishi and back our work with extended warranties. From honest estimates to clean job sites, our local team delivers comfort with integrity.