November 3, 2025
Parker, CO Heat Pump Not Cooling? 5 Key Reasons
Estimated Read Time: 8 minutes
Heat pump not cooling? You are not alone. When summer hits the Front Range, a heat pump that blows warm or lukewarm air can ruin your day. In this guide, our Denver team explains the five most common reasons your system stops cooling and how to fix each one safely. You will also learn when a quick DIY check is enough and when to call a pro to protect your warranty and comfort.
Why Your Heat Pump Stops Cooling: Quick Overview
A heat pump cools by moving heat out of your home. If any part of that process is blocked, dirty, or low on power, the result is weak or no cooling. Before digging in, set the thermostat to Cool, fan Auto, and target 72–75°F. Confirm breakers are on. If air is barely moving or the outdoor unit is silent, move to the sections below.
Key facts Denver homeowners should know:
- Heat pumps can be up to 400% more efficient than even the most efficient furnace when operating correctly.
- Combined heating and cooling heat pumps should receive maintenance twice a year for dependable performance.
Local note: Along the Front Range, cottonwood season and construction dust clog coils and filters faster than you expect. Spring temperature swings also stress systems that have not had a tune‑up.
1) Clogged Air Filter or Blocked Return
A dirty filter is the number one cause of a heat pump not cooling. Dust restricts airflow across the indoor coil. Low airflow means the coil cannot absorb heat, so you get warm air or icing.
What to check now:
- Inspect the filter. If you cannot see light through it, replace it.
- Confirm the filter faces the correct airflow direction arrow.
- Clear furniture or rugs away from return grilles.
- If you see ice on the indoor coil or lineset, turn the system Off and the fan to On for 60 minutes to defrost.
When to call a pro:
- Ice returns, the filter ices within a day, or you hear whistling at the return. These point to duct restrictions or an oversized filter rack that needs a retrofit.
Pro tip: In Denver, change basic 1 inch filters every 30–45 days in summer. High MERV filters need careful sizing to avoid choking airflow.
2) Outdoor Unit Is Dirty or Airflow Is Blocked
Your heat pump rejects indoor heat outdoors. If the condenser coil is matted with cottonwood fluff or landscaping blocks the fan, the system cannot dump heat and cooling stalls.
What to check now:
- Shut off power at the outdoor disconnect.
- Hose the coil from inside out using gentle pressure. Avoid bending fins.
- Keep 24 inches of clearance around the unit. Trim shrubs and lift mulch away from the base.
- Listen for the fan. A fan that hums but will not spin could have a failed capacitor.
When to call a pro:
- Repeated tripping of breakers, loud grinding, or visible oil stains on the refrigerant tubing. These suggest electrical or refrigerant issues.
Local tip: Cottonwood peaks in late May and June across Denver, Aurora, and Thornton. A mid‑season rinse can restore 10–20% lost capacity.
3) Thermostat or Control Settings Are Wrong
Simple settings can cause a heat pump not cooling. If the thermostat is in Heat, in Emergency Heat, or set to Fan On continuously, you may feel warm or neutral air.
What to check now:
- Mode must be Cool. Do not use Emergency Heat in summer.
- Set Fan to Auto to avoid blowing unconditioned air between cycles.
- Disable schedule holds that keep the setpoint too high.
- If you have a smart thermostat, confirm the system type is Heat Pump with cooling enabled.
When to call a pro:
- The thermostat loses power, reboots randomly, or the system short cycles every 3–5 minutes. A professional should check low‑voltage wiring, staging, and sensor calibration.
Upgrade insight: Smart thermostats with correct heat pump configuration can reduce runtime and improve humidity control. We install and calibrate leading models for Denver’s dry climate.
4) Low Refrigerant or a Refrigerant Leak
Refrigerant does not get used up. If levels are low, there is a leak. Low charge causes poor cooling, long runtimes, coil freezing, and rising energy bills.
Signs you might have a leak:
- Bubbles at braze joints or oily residue on the lineset.
- Sizzling or hissing sounds near the indoor or outdoor coil.
- Ice on the refrigerant line or evaporator coil.
What to do:
- Turn the system Off to prevent compressor damage.
- Call a licensed HVAC technician. We will pressure test, locate leaks with electronic detection, repair the line or coil, evacuate, and weigh in the factory‑specified charge.
Why this matters: Running low on refrigerant overheats the compressor. Replacing a compressor can cost more than half of a new system, so early diagnosis saves money.
5) Defrost, Reversing Valve, or Electrical Faults
A heat pump switches modes using a reversing valve. If the valve sticks, the unit can run in heat when you want cooling. Control boards, capacitors, and contactors also fail with age or surges.
Symptoms:
- Outdoor unit runs, but air from vents is warm in Cool mode.
- The system cools briefly, then stops, then restarts repeatedly.
- The outdoor fan runs but the compressor is silent.
Professional fixes may include:
- Testing low‑voltage control circuits and safeties.
- Measuring capacitor health and replacing failed parts.
- Inspecting and, if needed, replacing the reversing valve or coil.
- Updating firmware or settings on compatible smart controls.
Safety first: Electrical work must meet Denver and county code. Our licensed techs perform code‑compliant repairs and provide documentation for your records.
DIY Checks vs. Professional Service
Not every no‑cool event needs a major repair. Work through these basics before you schedule service:
- Filter is clean and correctly installed.
- Thermostat is in Cool, Fan Auto, and set 3°F below room temp.
- Breakers are On for the air handler and the outdoor unit.
- Outdoor coil is clean and has 24 inches of clearance.
- Supply and return vents are open in every room.
Call a professional if:
- Ice forms again after thawing.
- Breakers trip more than once.
- You hear grinding, buzzing, or smell burning.
- Rooms have big temperature differences or airflow is weak.
Prevent Breakdowns with Pro Maintenance
Heat pumps serve year round, so they need consistent care. The most effective and affordable fix is prevention.
What our tune‑up includes:
- Coil cleaning and airflow testing.
- Electrical testing of capacitors, contactors, and controls.
- Refrigerant performance check by superheat and subcooling.
- Drain cleaning and leak inspection.
- Thermostat calibration and duct system review.
Maintenance cadence:
- If you have a heat pump, the combined heating and cooling system should receive maintenance twice a year. One visit before cooling season and one before heating season keeps efficiency high and warranties valid.
Home Care Club advantage:
- This package includes annual inspections for your furnace, air conditioner, plumbing, and electrical systems at no extra charge. Club members also enjoy reduced costs on any needed repairs. Members get priority service, which matters on the hottest week in Denver, Aurora, or Boulder.
Repair or Replace: How to Decide
Sometimes a no‑cool call reveals bigger issues. Use these guidelines to decide your best path:
Consider repair when:
- The unit is under 10 years old.
- The repair is minor, like a capacitor or contactor.
- Energy bills have not spiked and comfort was good before the fault.
Consider replacement when:
- The system is 12–15 years old and needs a major part like a compressor.
- You have repeated refrigerant leaks on coils that are out of warranty.
- Rooms are uncomfortable due to duct design that a new variable‑speed system could overcome.
Why many Denver homeowners choose replacement:
- Modern high efficiency heat pumps are quieter, handle shoulder‑season swings well, and can integrate with smart thermostats for comfort and savings. We can install any brand you prefer and recommend Bosch for performance and reliability.
Financing and warranties:
- We offer transparent estimates and financing options so you can spread costs. Our work is backed by material and workmanship warranties, and we stand behind corrections if needed.
Local Expertise You Can Trust
Brothers Plumbing, Heating, and Electric has served Denver for decades with licensed HVAC pros, BBB accreditation, and thousands of positive reviews. We provide a two hour arrival window, same‑day appointments when available, and 24/7 emergency coverage. From Highlands Ranch to Longmont and Lafayette, we understand duct static issues in older brick homes and the airflow demands of newer high‑efficiency builds.
What To Expect During a Service Visit
- Arrival alert within your two hour window.
- Safety and performance inspection of indoor and outdoor units.
- Clear findings with photos and options. No pressure.
- On‑the‑spot repairs for common parts stocked on our trucks.
- Clean workspace and test run, plus maintenance and filter recommendations.
Staying proactive with maintenance and quick repairs keeps efficiency high. When your heat pump not cooling issue pops up, you now have a simple plan to restore comfort fast.
Special Offer
Special Offer: Save $50 on Heat Pump service. Use code HEATPUMP50 before 2025-11-05. Call (720) 994-7055 or schedule at https://www.brothersplumbing.com/. Applies to diagnostic or repair work performed on Heat Pumps. Same‑day and 24/7 emergency service available.
What Homeowners Are Saying
"We've had Brothers install both a furnace (a few years ago) and a heat pump for us, and have been thoroughly pleased. Their crew are knowledgable, professional, and really great to work with, and the equipment has been top notch. You can probably find cheaper HVAC service, but certainly not better."
–Stuart M., Heat Pump Installation
"Gannon and Anthony did a great job. They answered all my questions installation of our new heat pump, furnace and water heater. Bonus points for what I thought was going to be a 4 day job finishing in 2 and this is the cleanest any contractor has left my home. A+ with 2 thumbs up!"
–Nathan P., Denver
"Everyone has been Thoughtful and gave excellent service, kind & answered all my questions. Great at talking with me about the process so that I was informed. Anthony took his time problem solving the issue so that he could rule out many things. Andy came it he next day and really used his experience to get my heat pump to work. I appreciate Andy making my puppy feel safe."
–Donica S., Heat Pump Repair
"Gannon inspected our heat pump and water heater for code compliance and safety. He was polite and thorough. I enjoyed talking to him."
–Doug S., Inspection
Frequently Asked Questions
Why is my heat pump blowing warm air in Cool mode?
Wrong settings, low airflow, a dirty outdoor coil, or a stuck reversing valve can cause warm supply air. Confirm Cool mode and Fan Auto, replace the filter, and clear the outdoor coil. If issues persist, schedule a diagnostic to check refrigerant and controls.
How often should a heat pump be serviced in Colorado?
Twice a year. One visit before cooling season and one before heating season. This cadence keeps efficiency high, catches leaks early, and supports warranty terms, especially with heavy cottonwood and dust along the Front Range.
Can low refrigerant fix itself?
No. Refrigerant does not get used up. Low charge means a leak. Running the system can damage the compressor. Turn it off and call a licensed HVAC technician to find and repair the leak, then recharge to factory specs.
Should I run Emergency Heat in summer if cooling fails?
No. Emergency Heat disables the heat pump and uses electric or gas backup heat. That will make the home warmer and raise bills. Turn the system off if iced, thaw, and schedule service.
Will a smart thermostat help my heat pump cool better?
Yes, when configured correctly. Proper heat pump settings, staged control, and fan tuning can improve comfort and reduce runtime. A pro can install and calibrate it for your system and ductwork.
Conclusion
A heat pump not cooling usually comes down to airflow, dirty coils, control settings, refrigerant issues, or a failed component. With twice‑a‑year maintenance and prompt repairs, your system will stay efficient and reliable across Denver’s hot spells.
Ready to get cool again in Denver, Aurora, or Boulder? We are here to help today.
Book Service Now
- Call (720) 994-7055 for same‑day or 24/7 emergency heat pump help.
- Schedule online at https://www.brothersplumbing.com/.
- Coupon: $50 Off Work Performed on Heat Pumps. Use code HEATPUMP50 before 2025-11-05.
Join the Home Care Club for priority service and reduced repair costs. Get your system tuned, cleaned, and cooling fast.
About Brothers Plumbing, Heating, and Electric – Denver Brothers is Denver’s trusted home services team for HVAC, plumbing, and electrical. We are BBB accredited with an A+ rating and were recognized among Colorado Titan 100 in 2024. Expect licensed techs, clear pricing, financing options, and a two hour arrival window. We offer 24/7 emergency service and stand behind our work with strong material and workmanship warranties. Local service for Denver, Aurora, Boulder, and beyond.