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Heat pump trouble

My Heat Pump Isn't Keeping the House Warm

Heat pumps work differently from furnaces, so some behaviors that look like problems are normal. Others mean the system needs a closer look.

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Technician servicing an outdoor AC unit beside a house with a brick foundation

Quick answer

A heat pump may feel like it isn't heating because it delivers gentler warmth than a furnace, runs a defrost cycle in cold weather, or leans on backup heat during a cold snap. Real problems include a dirty filter, an outdoor unit iced over or blocked, low refrigerant, a stuck reversing valve or a failed defrost control. Start with the thermostat mode and the outdoor unit.

What may be going on

Possible causes

  1. Defrost cycle

    On raw winter days, the outdoor coil collects a layer of frost. The system briefly reverses to melt it, which can send cooler air indoors and create steam outside. That is normal.

  2. Outdoor unit iced over

    If ice stays on the outdoor coil for hours, the defrost control, sensor or refrigerant charge may be failing.

  3. Backup heat issues

    During cold snaps, auxiliary heat strips help the heat pump. If those fail, the house may struggle to stay warm on the coldest nights.

  4. Reversing valve problem

    The valve that switches between heating and cooling can stick, leaving the system blowing cool air in winter.

  5. Low refrigerant or airflow

    A leak or a clogged filter reduces the heat the system can move indoors.

Safe checks you can make

  • Make sure the thermostat is set to Heat, not Cool or Emergency Heat, with the setpoint a few degrees above room temperature.
  • Replace the air filter if it is dirty.
  • Rake leaves or snow away from the outdoor unit and check that a gutter overhead isn't dripping straight onto it.
  • Watch the outdoor unit: a short period of steam and quiet fan during defrost is normal.
  • Check the breakers for the outdoor unit and air handler, and reset one once if tripped.

What not to do

  • Don't chip or scrape ice off the outdoor coil; the fins and tubing damage easily.
  • Don't pour hot water on the outdoor unit or open its panels.
  • Don't add refrigerant from a recharge kit.
  • Avoid parking the thermostat on Emergency Heat for days unless a technician recommends it.

When to call a professional

If the outdoor unit stays coated in ice for hours, the system blows cool air constantly, or the auxiliary heat light stays on even in mild weather, a technician should test the defrost controls, refrigerant and valves.

Heat pumps are common across Birmingham, AL and nearby suburbs. Call to get connected with an independent local HVAC provider, and mention whether you need heat pump repair or a full look at the heating side.

  • Thick ice on the outdoor unit that doesn't clear after defrost.
  • Cool air from the vents with the system set to Heat.
  • The auxiliary heat indicator stays on most of the time.
  • The outdoor unit doesn't run while the indoor fan does.

What an HVAC provider may inspect

  • Defrost board, sensor and timer operation
  • Reversing valve function
  • Refrigerant pressures and leak checks
  • Auxiliary heat strips and controls
  • Outdoor fan and compressor operation

Keeping it from happening again

Keeping the outdoor unit clear, replacing filters regularly and having the heat pump checked before winter helps it handle cold snaps. Auxiliary heat is the system's helper that turns on automatically when the heat pump needs a boost. Emergency heat is a manual setting that runs only the backup heat and is meant for when the heat pump itself has a problem. For homes with gas furnaces instead, see furnace not heating.

Where to go next

Related serviceHeat Pump Repair

Frequently asked questions

Heat Pump Not Heating: questions homeowners ask

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Steam usually means the heat pump is in defrost mode, melting frost off the outdoor coil. It typically lasts a few minutes and is normal. Thick ice that never clears, though, is a sign the defrost system needs checking.

Auxiliary heat comes on automatically to help the heat pump on cold days or when the house needs to warm up quickly. Emergency heat is a setting you choose, and it runs only the backup heat. Use it only when the heat pump itself isn't working.

Supply air from a heat pump runs noticeably cooler than air from a gas burner, so it can feel lukewarm even when the system is working well. If rooms aren't reaching the setpoint, that is worth having checked.

Still not sure what's wrong?

Call and describe what you're seeing. You'll be connected with an independent HVAC provider serving homes in the Birmingham, AL region.

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