Five field tested checks homeowners can run right now. Safe inspection steps, what photos to send with a service call, and when…

If your heat pump is not heating, the most likely culprits are a thermostat set wrong, a dirty filter blocking airflow, a frozen outdoor unit stuck in defrost, a tripped breaker, or a low refrigerant charge. Most of these you can check yourself in a few minutes. Refrigerant and reversing valve problems need an EPA-certified technician by law, so snap photos of your thermostat reading and the outdoor unit before you call.

TL;DR:

• Most heating failures are caused by simple issues like a dirty filter, incorrect thermostat settings, or a tripped breaker, which homeowners can check quickly.
• Persistent outdoor ice buildup may indicate a stuck defrost cycle or drainage problem, requiring professional diagnosis if it does not clear within 15 minutes.
• Refrigerant leaks, reversing valve faults, and compressor issues necessitate EPA-certified technicians, especially when signs include oily residues, hissing sounds, or reduced heating capacity.
• Regular maintenance such as monthly filter checks, sealing duct leaks, and clearing debris improves heat pump reliability and minimizes emergency repairs.
• Always record thermostat readings, take photos of the outdoor unit, and stop attempting repairs if electrical problems recur or safety issues like odors or sparking appear.

Five quick checks to try right now

Before you assume the worst, run through these checks. Most take less than 30 minutes combined and will tell you whether you’re dealing with something simple or something that needs a professional.

1. Check the thermostat: confirm it’s set to “heat” (not “auto” or “cool”), the setpoint is above room temperature, the fan is set correctly, and the batteries are fresh.
2. Inspect the air filter: hold it up to a light. If you can’t see through it, replace it. Check supply and return vents for obstructions like furniture or curtains.
3. Look at the outdoor unit: is the compressor running? Are the fan blades spinning? Is there ice building up on the coils instead of melting off during a normal defrost cycle?
4. Check your electrical panel: look for a tripped breaker, and find the outdoor disconnect switch near the condenser to confirm it’s in the “on” position.
5. Check the condensate pan and float switch: a full pan can trip a safety switch that shuts the whole system down.

Pro Tip: Take a photo of your thermostat’s current reading and setpoint before you touch anything. If you end up calling a technician, that single detail saves diagnostic time.

Common causes: how each one stops heating, signs to look for, DIY vs pro

Each of these problems interrupts heating in a different way, and the signs you see point to different fixes.

• Thermostat errors: a dead battery, a wrong mode setting, or a miscalibrated sensor can make the system think the house is already warm. Try a basic reset (remove batteries for 30 seconds, reinsert) and watch whether the display reads correctly. This is safe for any homeowner to try.
• Airflow problems: a dirty filter is one of the most common causes, and restricted airflow from a clogged filter can cut system efficiency by up to 15 percent. Blocked returns, a weak blower motor, or leaky ductwork all starve the system of the air it needs to move heat efficiently. Typical homes lose 20 to 30 percent of conditioned air through duct leaks, which means a perfectly good heat pump can still leave rooms cold if the ducts feeding them are leaking.
• Frozen outdoor unit and defrost cycle issues: some icing is normal. Heat pumps run a defrost cycle that typically lasts between 5 and 15 minutes 5 to 15 minutes, during which the outdoor fan stops and the system may briefly reverse to melt ice. Persistent icing that doesn’t clear, or a unit that’s frequently encased in ice, points to a stuck defrost control, a drainage problem, or water dripping onto the coil from above (like a deck overhang or an upstairs unit).
• Refrigerant leaks and reversing valve faults: hissing sounds, oily residue near fittings, reduced heating capacity, and ice forming even with no cold weather in sight are all signs. EPA regulations require certified technicians to handle refrigerant, and homeowners should never try to “top off” a system themselves. The right fix is finding and repairing the leak, not just adding refrigerant.
• Power and control faults: a tripped breaker, a blown fuse, a flipped outdoor disconnect switch, or an indoor service switch that got bumped can all cut power without any obvious warning sign.
• Undersized systems or poor distribution: if your system constantly relies on auxiliary heat and never quite reaches the setpoint, the unit itself may be too small for the house, or the ductwork may be distributing air poorly. A contractor addressing this will typically run a Manual J load calculation and inspect duct design rather than just swapping parts.

How to check safely and what to record for a service call

A little caution during your inspection protects you and gives a technician useful information right away.

1. Stand back from the outdoor unit’s moving parts and simply observe: is the fan spinning, is there ice, do you hear grinding or rattling?
2. Photograph any ice buildup, oily spots near refrigerant lines, or unusual frost patterns.
3. Replace the filter with the system powered down, and check that vents and returns are clear of furniture or rugs.
4. Reset a tripped breaker once. If it trips again immediately, stop and call a professional instead of resetting repeatedly, since that can indicate an electrical fault.
5. Write down your thermostat’s readout, any error codes on the display, and how long the system ran before the problem started.

Pro Tip: A short video of the outdoor unit (10 to 15 seconds) showing the fan, any ice, and audible sounds often tells a technician more than a phone description ever could.

When to call a licensed HVAC professional (and what they’ll do)

Some signs mean it’s time to stop troubleshooting and pick up the phone.

• Burning smells, chemical odors, or visible sparking from the indoor or outdoor unit.
• Ice that doesn’t clear after a full heating cycle, or forms again within hours of clearing.
• Hissing sounds, oily residue, or a noticeable drop in heating capacity, all signs of a possible refrigerant leak.
• A compressor that won’t start even though power is confirmed at the breaker and disconnect.

A technician will check refrigerant pressure, test the reversing valve, inspect the compressor and blower motor, look for duct leakage, and in some cases run a Manual J sizing assessment to see if the equipment matches the house. If something feels unsafe, like a burning smell, turn the system off at the breaker and call for service rather than waiting.

Maintenance and prevention checklist

Most heat pump failures are preventable with a few habits throughout the year.

• Check or replace the filter monthly, especially during heavy heating season.
• Schedule a professional inspection each fall before cold weather hits, which ENERGY STAR recommends as part of a seasonal maintenance checklist.
• Keep the outdoor unit clear of leaves, snow, and debris, and shield it from dripping water without fully covering it.
• Seal and insulate accessible ductwork, since typical homes lose 20 to 30 percent of conditioned air through duct leaks, a loss that undermines even a well-running system.
• If you live somewhere with harsh winters and rely on a heat pump as your main heat source, ask a contractor about cold-climate equipment and proper sizing, since field studies show performance varies widely and undersized systems often lean heavily on auxiliary heat. For more homeowner-level troubleshooting on airflow and filter issues, this guide to common HVAC issues covers similar ground.

From Ernie M, what we see in the field and honest advice

In my years running service calls, the most common cause isn’t a broken part, it’s a skipped filter change or an ignored defrost cycle that homeowners assume is a malfunction. I’ve also seen costly damage from well-meaning attempts to add refrigerant without finding the leak first. Before you call anyone, including us, gather the thermostat reading and a photo of the outdoor unit. It genuinely speeds up the visit and keeps the estimate honest.

— Ernie M

How Upright Construction & HVAC can help

If you’ve run through the checks above and your heat pump still isn’t heating the way it should, a proper diagnosis saves you from guessing. We handle heat pump troubleshooting, repair, and seasonal maintenance, including emergency service when something can’t wait until morning.

When you book a visit, expect a straightforward inspection and a clear, upfront quote before any work starts. If your system needs ongoing care, our maintenance plans cover the seasonal checkups that catch small issues early. For a direct repair visit, you can schedule HVAC repair and get a technician out to look at the problem firsthand.

FAQ

Why is my heat pump blowing cold air when the heat is on?

This is often normal during a defrost cycle, when the system briefly reverses to melt ice off the outdoor coil and air coming from the vents feels cool for a few minutes. If cold air continues for longer than a normal defrost cycle or happens constantly, check your thermostat mode first, then suspect a refrigerant or reversing valve issue.

How do you reset a heat pump?

Turn the system off at the thermostat, then switch off power at the breaker for about 30 seconds before turning it back on. If the unit doesn’t respond normally afterward or the breaker trips again, stop resetting it and call a technician instead.

Why is my heat pump fan running but no heat?

A fan that runs with no heat often points to a refrigerant problem, a failed reversing valve, or a compressor that isn’t engaging, all of which typically require a certified technician to diagnose. Before assuming the worst, confirm the thermostat is set to heat mode and the setpoint is above room temperature.

What is the most common problem with heat pumps?

Airflow restriction from a dirty filter is one of the most frequent issues homeowners run into, since a clogged filter can reduce efficiency by up to about 15 percent. Frozen outdoor coils and skipped seasonal maintenance are close behind as common causes of heating complaints.

Sources

• EPA — Section 608: EPA’s refrigerant management program questions and answers
• Duct sealing — ENERGY STAR