Rheem Heat Pump Not Heating: Causes, Fixes & Costs
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Rheem heat pump not heating: what it means
“Not heating” is a symptom, not a numbered Rheem fault code. It means the heat pump is either not running in heat mode or running without delivering warm air.
A Rheem heat pump heats by reversing its refrigerant flow. A reversing valve, controlled by the thermostat’s O (or B) signal, makes the outdoor coil absorb heat and the indoor coil release it. When that process fails, the house stays cold. Typical failures include:
- No call for heat from the thermostat
- The outdoor unit not starting
- The reversing valve staying in cooling position
- A low refrigerant charge
- Auxiliary heat not covering cold weather
If your unit is also flashing a fault light, or is iced over and not defrosting, see those dedicated pages first. This page covers heat pumps that are not frozen and show no clear fault code, but still produce no meaningful heat.
How the system reports problems depends on the model. Older Rheem and Ruud defrost boards give little or no feedback. EcoNet and communicating systems show specific alerts on the thermostat, which a technician can use to narrow the cause quickly.
Rheem heat pump not heating: common causes, ranked by probability
- Thermostat setting or configuration. The thermostat may be set to Cool or Off, or the setpoint may be below room temperature. A newly installed thermostat may also have the wrong reversing-valve setting (O vs. B). Rheem heat pumps energize the reversing valve in cooling (O). A thermostat set to B runs cooling when you call for heat.
- Dirty air filter or blocked airflow. Restricted airflow cuts heat delivery. It can also trip high-pressure protection in heat mode, because the indoor coil acts as the condenser.
- Outdoor unit not running (power or electrical). Possible causes include:
- A tripped breaker or outdoor disconnect
- A failed run capacitor
- A burned or pitted contactor
- A control-board lockout
- Reversing valve or solenoid failure. The valve is stuck in cooling position, or the solenoid coil has failed. The outdoor unit runs, but the house gets cool air.
- Low refrigerant charge (leak). The system runs long and produces lukewarm air, sometimes with frosting patterns that don’t match normal defrost.
- Auxiliary or emergency heat failure. Below the balance point, the heat pump alone can’t keep up. Common culprits are failed heat strips, sequencers, limits, or auxiliary-heat wiring in the air handler. The house falls behind in cold weather even though the heat pump works.
- Compressor failure. The fan runs but the compressor won’t start, or it hums and trips on overload. This is less common, and it’s diagnosed only after the capacitor, contactor and controls check out.
- Undersized system or ductwork leaks. These cause chronic underperformance rather than a sudden failure. Typical signs are leaky ducts in an attic or crawlspace, or a unit too small for the home.
How to fix Rheem heat pump not heating: safe checks first
- Thermostat mode and setpoint. Confirm it’s set to Heat, not Cool, Auto or Off. Set it 3–5°F above room temperature.
- Thermostat batteries. Replace them if the display is blank or dim, or shows a low-battery icon.
- Air filter. Check the filter at the air handler or return grille. Replace it if it’s gray, clogged, or more than about three months old.
- Breakers and switches. Check the breakers for both the outdoor unit and the indoor air handler. Many homes also have a separate breaker for the auxiliary heat strips. Reset a tripped breaker once only. If it trips again, leave it off and call a pro.
- One reset. Turn the thermostat to Off and switch off both breakers for about five minutes. Restore power, set the thermostat to Heat, and wait 5–10 minutes. Some Rheem boards enforce a short-cycle delay before the compressor will start. Don’t repeat the reset.
- Registers and returns. Make sure supply registers are open and return grilles aren’t blocked by furniture or rugs.
- Outdoor unit clearance. Clear away snow, leaves or debris piled against the coil, from the outside only. Keep about two feet of clearance. Don’t open the unit.
- Panels. Confirm the air-handler access panels are fully seated. A loose panel can keep the blower from running on some units.
- Condensate. If the air handler shares a pan or drain with a furnace or has a float switch, check that the drain isn’t backed up. A tripped float switch can shut the system down.
- Emergency heat test. Set the thermostat to Emergency Heat (EM Heat) briefly. If warm air comes out, the auxiliary heat works and the problem is on the heat pump side. Tell your technician what you found. Emergency heat is expensive to run, so use it only as a stopgap.
How a technician will diagnose it
A competent tech will typically work through these steps:
- Verify the call for heat. They confirm the thermostat is sending Y (compressor) and the correct O/B signal. On EcoNet or communicating systems, they read stored alerts and fault history.
- Check outdoor unit power and controls. This includes:
- Line voltage at the disconnect
- 24V control voltage at the contactor
- Whether the contactor pulls in
- Defrost or control-board LED status and any lockout history
- Test the capacitor and compressor. They measure capacitance against the rating and check compressor windings and amp draw.
- Test the reversing valve. They measure line temperatures across the valve and check voltage and resistance at the solenoid coil. They also observe whether the valve shifts when the thermostat switches between Heat and Cool.
- Check the refrigerant charge. Using gauges or digital probes, they measure pressures, superheat and subcooling against Rheem’s heating charging chart. If the charge is low, they should leak-search before adding refrigerant. Topping off without finding the leak is a red flag.
- Check auxiliary heat. They measure amp draw on each heat strip and test sequencers, relays and limits.
- Measure airflow and temperature rise. They check static pressure and the supply-to-return temperature difference.
Sanity check on quotes: Be wary of a reversing-valve or compressor diagnosis given without electrical tests and pressure readings. The same goes for refrigerant added with no mention of a leak.
Symptom, cause and what to do
| Symptom | Likely cause | DIY action | Technician job |
|---|---|---|---|
| Nothing runs, thermostat blank | Dead batteries or no power | Replace batteries; check breakers once | Check transformer, fuse, low-voltage wiring |
| Air blows cool, outdoor unit running | Thermostat on Cool, wrong O/B setting, or stuck reversing valve | Confirm Heat mode | Correct O/B setup; test solenoid; replace valve |
| Indoor fan runs, outdoor unit silent | Tripped breaker, bad contactor or capacitor, board lockout | Reset breaker once; one power-cycle reset | Test and replace capacitor or contactor; diagnose lockout |
| Outdoor fan runs, compressor hums or is silent | Failed capacitor or compressor problem | None beyond one reset | Test capacitor and windings; replace parts or compressor |
| Lukewarm air, very long run times | Low refrigerant or dirty filter | Replace filter | Leak search, repair, recharge per Rheem chart |
| Fine in mild weather, cold below freezing | Auxiliary heat strips or sequencer failed | Test Emergency Heat; check aux heat breaker | Test and replace heat strips, sequencer, limits |
| Weak airflow at all registers | Clogged filter or blower issue | Replace filter; open registers | Check blower motor, coil, static pressure |
| System stops, water near air handler | Condensate float switch tripped | Clear visible drain line | Clear trap, check pan and switch |
Rheem heat pump not heating repair cost
Typical US installed prices, parts plus labor. Prices vary by region and warranty status. Rheem parts warranties often cover components, but not labor.
| Repair | Typical cost |
|---|---|
| Filter replacement | $10–$50 (DIY) |
| Thermostat batteries | $5–$10 (DIY) |
| New heat pump thermostat | $40–$250 DIY, $150–$450 installed |
| Service call / diagnostic | $90–$250 |
| Run capacitor | $150–$400 |
| Contactor | $150–$350 |
| Reversing valve solenoid coil | $150–$400 |
| Defrost or control board | $300–$800 |
| Heat strip / sequencer repair | $200–$700 |
| Refrigerant leak search and repair, plus recharge | $400–$1,500+, depending on leak location and refrigerant type |
| Reversing valve replacement | $900–$2,500 (brazing, evacuation, recharge) |
| Compressor replacement | $1,800–$4,000+; often weighed against a new outdoor unit |
Related codes
- Rheem Heat Pump Flashing Light: Causes & Fixes. Read this if the outdoor or indoor board shows a fault light alongside the no-heat problem.
- Rheem Heat Pump Frozen, Not Defrosting: Causes & Fixes. Read this if the outdoor coil is encased in ice.
- Rheem Furnace Runs Constantly, Not Enough Heat: Fixes. Relevant for dual-fuel systems where a Rheem gas furnace provides backup heat.
- Rheem Furnace Blowing Cold Air: Causes & Fixes. Covers the gas-furnace side of dual-fuel systems.
Parts & tools for this fix
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Frequently asked questions
Why is my Rheem heat pump running but blowing cool air?
Heat pump supply air often runs around 90–100°F, which can feel cool on your hand, especially in cold weather. If the air is truly at room temperature or colder, the cause could be a thermostat set to Cool, a stuck reversing valve, low refrigerant, or an outdoor unit that isn't running.
Is it normal for a Rheem heat pump to struggle when it's very cold outside?
Yes. Output drops as outdoor temperatures fall, and most systems rely on auxiliary electric heat strips or a furnace below a balance point, often in the 25–35°F range. If the house won't stay warm in mild weather, or the auxiliary heat never engages, something is wrong.
Can I reset my Rheem heat pump myself?
You can turn the system off at the thermostat, switch off the outdoor and indoor breakers for about five minutes, then restore power once. If it still doesn't heat, or a fault reappears, stop and call a technician. Repeated resets can damage the compressor.
Does the not-heating problem clear on its own?
Not heating isn't a single fault code, so there's no defined auto-reset. Some protective lockouts on Rheem outdoor boards, such as pressure-switch or compressor-protection lockouts, clear after a timed delay or a power cycle, depending on the board. Persistent problems need diagnosis.
How much does it cost to fix a Rheem heat pump that won't heat?
Simple fixes like a filter or thermostat setting cost little or nothing. Capacitors and contactors usually run $150–$400 installed. Reversing valves and refrigerant leak repairs often cost $800–$2,500. Compressor replacement can approach the cost of a new outdoor unit.