Rheem Heat Pump Error Codes List: Every Code Explained
Every Rheem heat pump error code we could verify against Rheem's own documentation — what it means, what usually causes it, and the first fix to try — in one table. Codes differ between model series, so treat your model's tech sheet as the final word.
How to read and retrieve error codes on Rheem heat pumps
The ICC shows everything on a dual 7-segment LED display on the outdoor control: one letter for operating states (0 standby, c/C cooling stages, h/H heat-pump stages, d defrost, t test), two digits for faults, and an alternating L + number for lockouts — Rheem warns the codes must be read from the correct side of the display to avoid misreading them. The control also keeps a fault history a technician can recall in its test/fault-recall mode, which matters because pressure trips that self-clear leave evidence there. On EcoNet communicating systems the same events additionally appear at the EcoNet control as A/T alert numbers (the variable-speed manual pairs its display codes with alerts such as A907 under-voltage, A906 over-voltage and A/T923 high pressure). Quote the board display first — it is the primary record; the letter case matters (lower-case h is first-stage heat, upper-case H is second-stage).
The complete Rheem heat pump error code list
| Code | Meaning | Most likely cause | First fix |
|---|---|---|---|
| 0 | Standby — not a fault: the ICC display reads 0 when there is no command for unit operation | Normal idle state between demands | No repair needed. If a demand is active and the display stays at 0, the call is not reaching the outdoor control — thermostat/control wiring is technician diagnosis |
| 01 | Long run time (two-stage ICC list) — the compressor has run continuously for more than 18 hours in cooling mode | Low refrigerant charge, substantial duct leakage, a dirty indoor filter, or a dirty outdoor coil (the list's stated causes) — anything that makes the unit unable to satisfy the call | Owner checks: filter and outdoor coil cleanliness. Charge and duct-leak diagnosis are technician work. 01 is the unit telling you it ran all day and lost |
| 02 | High pressure (two-stage ICC list) — the compressor limit has opened four times within a call | Repeated high-pressure events within one demand — see code 29 for the underlying causes (dirty coil, dead fan, restriction, overcharge) | Treat as 29 that has already repeated four times: coil/fan/airflow first, then certified pressure diagnosis |
| 03 | Short cycling (two-stage ICC list) — the run time of each of the past four cycles was less than three minutes (on the variable-speed manual, repeated short runs surface as the '3' fault, reset by removing low-voltage power from the outdoor control board) | Oversized equipment, thermostat placement/anticipator problems, a control or sensor chattering the demand, or a protection device cycling the compressor | Note the pattern for the technician — what starts and stops it. Short cycling is a compressor-life fault, not a nuisance code |
| 05 | Open circuit (two-stage ICC list) — the ICC has had a protector trip lasting longer than 4 hours | A compressor circuit that opened (protector, wiring or contactor) and never re-made within four hours | Technician circuit diagnosis; a four-hour open is a failed component, not a transient |
| 06 | Compressor open start circuit (two-stage ICC list) — current is measured in the run circuit but not in the start circuit | Failed start capacitor/relay or open start-circuit wiring | Technician start-circuit work. Four occurrences in one call escalate to L6 |
| 07 | Compressor open run circuit (two-stage ICC list) — current is measured in the start circuit but not in the run circuit | Open run-circuit wiring, capacitor failure, or a compressor run-winding fault | Technician diagnosis, as for 06. Four occurrences escalate to L7 |
| 09 | Low secondary volts — the secondary voltage at R and C is below 18 VAC (both ICC generations) | An overloaded control transformer or low line voltage dragging the 24 V supply down (the (‐)P20 manual's stated causes) | Technician low-voltage diagnosis. A starved control drops calls and logs phantom faults |
| 21 | Low pressure control open — the ICC detects the LPC is open. Note: the LPC is ignored during parts of the cycle (the defrost/ mode-change windows the manual defines), so a genuine 21 is read in steady operation | Low refrigerant charge; in cooling a frozen indoor coil or a non-running indoor blower; in heating a frozen outdoor coil; or an expansion valve not operating correctly (the (‐)P20 manual's stated causes) | Owner checks: filter, indoor blower running, no ice on either coil. Charge and expansion-valve work are certified-technician work. Three opens in one call escalate to the L21 lockout |
| 27 | Low line voltage or no line voltage fault (on the variable-speed control: AC input under voltage, inverter alert A907) | Supply voltage missing or sagging at the unit: disconnect/breaker state, utility sag, or supply wiring dropping voltage under load | Check incoming line voltage at the disconnect and unit and check wiring connections (the manual's stated actions); recurring sags are electrician work |
| 28 | High line voltage fault (variable-speed control: AC input over voltage, inverter alert A906; the ICC restarts the compressor when voltage falls back to ≤252 VAC after holding it off above that) | Utility supply voltage genuinely too high, or a supply problem (e.g. lost neutral) pushing voltage up | Check line voltage. Sustained over-voltage is a utility/electrician problem — do not keep running the inverter into it |
| 29 | High pressure control open — the ICC detects the HPC is open (variable-speed control pairs it with inverter alert T923) | In cooling: a dirty outdoor coil or an outdoor fan not running. In heating: a dirty indoor coil or filter, the indoor blower not running, a liquid-line restriction, or excessive refrigerant charge (the manuals' stated causes) | Owner checks: outdoor coil cleanliness and fan operation in cooling; filter and indoor blower in heating. Restriction and charge work are certified-technician work. Three opens in one call escalate to L29 |
| 30 | Fuse open (two-stage ICC list) — the ICC detects its on-board 3-amp fuse is open | Low-voltage wiring at R and C damaged or miswired, shorting the control circuit (the list's stated cause; the (‐)P20 flowchart likewise sends a lit-display check to the 3 A fuse on the ICC board) | A technician repairs the low-voltage short first and only then replaces the fuse |
| 80 | Low airflow (two-stage ICC list) — the ICC detects the indoor unit is not providing the minimum airflow the outdoor unit requires | A misapplied/wrong indoor air mover (the list's stated cause), or airflow far below the matched system's requirement | Verify the indoor unit is the approved match for the outdoor unit; airflow measurement is technician work |
| 83 | Condenser (outdoor) coil temperature fault — the coil sensor detects an abnormally low or high coil temperature | A failed coil thermistor, or a sensor not installed correctly on the control (the manuals' stated causes) | A technician checks the sensor's installation on the control and replaces the sensor if it reads out of range |
| 84 | Outdoor ambient temperature fault — the ambient sensor detects an abnormally low or high outdoor temperature reading (variable-speed control: alert T952) | A failed ambient thermistor, or a sensor baking in an abnormally hot placement (the (‐)P20 manual suggests checking unit placement and re-reading when ambient drops) | Check placement, then sensor replacement — technician work. Ambient readings steer defrost and capacity decisions, so a lying sensor corrupts both |
| 93 | Internal/config control fault — on the two-stage ICC list 93 is the internal control fault (control not functioning properly; replace the control). On the variable-speed control the same display is 'configuration data restore failure' (alert A950): check the control for proper system operation, replace if faulty | An internal failure of the ICC, or (variable-speed) its stored configuration data failing to restore | Control replacement is technician work, and on communicating models the model data must be preserved/transferred or the new control adds a d1 to the 93 |
| C | Cooling operation — an operating display, not a fault: lower-case 'c' = first-stage cooling, upper-case 'C' = second-stage cooling (a flashing letter means the 3-minute anti-short-cycle timer or 30-second minimum run timer is active) | A normal cooling command from the thermostat — the stage shown is the stage the system is running | No repair needed; a flashing letter simply means the unit is waiting out its timer — wait for it to expire (a technician can defeat the delay with the TEST button) |
| H | Heat pump heating — an operating display, not a fault: lower-case 'h' = first-stage heat (compressor heating without auxiliary heat), upper-case 'H' = second-stage heat (a flashing letter means the anti-short-cycle or minimum-run timer is active) | A normal heat-pump heating command from the thermostat — the stage shown is the stage the system is running | No repair needed |
| L4 | Locked rotor lockout (two-stage ICC list) — four consecutive protector trips with an average run time under 15 seconds; the ICC has locked the compressor out (display alternates L and 04). This active-protection mode must be manually reset | A compressor that cannot start turning, or start-circuit failure imitating it on every attempt | Technician start-circuit and compressor diagnosis BEFORE the manual reset — resetting into a locked rotor just repeats the four damaging attempts |
| L6 | Open start circuit lockout (two-stage ICC list) — the open-start condition has occurred four times in one call and the ICC has locked the compressor out (display alternates L and 06). Must be manually reset | The code 06 fault, unhealed across four attempts | Repair the start circuit first, then reset — the lockout is the control refusing a fifth attempt |
| L7 | Open run circuit lockout (two-stage ICC list) — the open-run condition has occurred four times in one call; compressor locked out (display alternates L and 07). Must be manually reset | The code 07 fault, repeated | Repair before reset, as for L6 |
| L21 | Active protection — low pressure control trip lockout (display alternates/flashes L and 21; the (‐)P20 manual writes it 21L): the LPC has opened three times in the same call — in heating, three opens within 120 minutes bring the hard-lockout form. This mode must be manually reset | The code 21 family, three times in one demand | Fix the 21 cause (charge, airflow, ice, expansion valve) before the manual reset; the ICC locked the compressor out specifically to stop a fourth low-pressure run |
| L29 | Active protection — high pressure control trip lockout (display alternates/flashes L and 29; written 29L on the variable-speed control, EcoNet alert A/T923): the HPC has opened three times in the same call and the ICC has locked the compressor out. Must be manually reset | The code 29 family, three times in one demand | Correct the 29 cause before the manual reset — a high-pressure lockout is the compressor's protection against its most damaging operating state |
| P | Protector trip (two-stage ICC list) — a command for compressor operation is present but no current is measured to the compressor: the compressor's protector is open | The compressor protector opened (overheat/overload) and has not yet re-closed | Let the compressor cool; why the protector opened is technician diagnosis. Repeated protector trips escalate — four consecutive short trips become lockout L4 |
| d | Defrost active — an operating display, not a fault: the unit is undergoing a defrost cycle | Normal winter operation: on ICC models the demand-defrost algorithm (built into the ICC — no separate defrost board) has decided the outdoor coil needs defrosting | No repair needed. On the documented variable-speed sequence the outdoor fan stops, auxiliary heat is energised indoors, and the cycle ends at the termination temperature (factory 60°F) or after 14 minutes |
| d1 | No model data / no shared data — the ICC has no valid model (memory) card data, so it does not know what unit it is controlling | The memory/model data card is missing, disconnected, or was not transferred when the control was replaced | Fit the correct memory card for the exact model (the manuals' stated fix: 'replace memory card with correct system information'). Never borrow another unit's card |
How to reset / clear error codes on Rheem heat pumps
Rheem splits its faults into self-clearing reports and Active Protection lockouts. Trips such as 21 (low pressure control open) and 29 (high pressure control open) are reports; three opens of the same control in one call convert them to the flashing L-code lockouts (L21, L29), and Rheem marks those modes in bold in its manuals: this mode of active protection must be manually reset. The compressor start/run family escalates identically (06→L6, 07→L7, protector trips→L4 locked rotor). Manual reset means removing and restoring power at the unit once the cause is fixed — Rheem does not provide a thermostat gesture that clears an active-protection lockout, by design. Status letters (0, c/C, h/H, d) never need resetting.
How to diagnose any Rheem heat pump code
Work the problem in this order — and stop where the refrigerant circuit, the compressor or mains wiring begins, because those belong to a licensed HVAC technician with gauges: (1) record the code exactly, and note where it appeared — the outdoor board's LED, a communicating wall control, or an app — because one heat pump can report the same fault three different ways; (2) run the free checks first: the air filter is clean, the indoor coil is not iced over, the outdoor unit is clear of leaves, snow and debris, both breakers are on, and the condensate drain is not lifting a float switch; (3) remember that defrost is not a fault — in cold weather the outdoor fan stops, the unit steams and hisses and the indoor air cools for a few minutes while frost melts off the outdoor coil; a defrost that never ends, or ice that never clears, is the fault, not the defrost itself; (4) clear the code once and watch a full heating cycle from the start — the stage that stops (outdoor fan, compressor, defrost, auxiliary heat) names the fault family; (5) pressure lockouts, reversing-valve faults and compressor faults are diagnosed with gauges and a meter on the sealed circuit — never "top up" refrigerant to make a code go away, because a heat pump losing charge has a leak, and the code is protecting the compressor from it.
Demand defrost inside the ICC: 35 degrees, 34 minutes, and a 60-degree finish
On ICC-equipped Rheem heat pumps there is no separate defrost board to blame: the demand-defrost algorithm lives inside the Integrated Compressor Control, which monitors outdoor ambient temperature (OAT) and outdoor coil temperature to decide when a defrost is required. The variable-speed manual states the initiation conditions exactly, and all three must hold: the outdoor coil temperature is below 35°F; the compressor has operated for at least 34 minutes with the coil temperature below 35°F; and the defrost algorithm determines a defrost is required. When they are met, the sequence is choreographed for noise as much as for ice: the inverter changes the compressor to a predetermined reversing-valve switching speed and holds it for a 30-second noise-abatement period, the reversing valve switches, the outdoor EXV opens to its model-data maximum, auxiliary heat (W) is energised to temper indoor air, the outdoor fan is de-energised, and the compressor ramps to defrost speed for the duration. Termination is a temperature, not a timer preference: the defrost continues until 14 minutes have elapsed or the coil reaches the termination temperature — factory-set at 60°F, changeable to 50, 60, 70 or (per the dip-switch table) other settings by relocating dip switches on the ICC. Exit mirrors entry: another 30-second noise-abatement hold, the valve switches back, the fan restarts, auxiliary heat drops, and the compressor runs at oil-circulation speed for six minutes before normal heating resumes. The failure fallbacks are documented with the same precision. If the ambient sensor fails, the control initiates a defrost every 34 minutes in heat mode whenever the coil is below 35°F — a fixed metronome replacing judgement. Technicians can force the issue two ways: pressing TEST for one second with the unit running in heat-pump mode enters defrost until termination or 14 minutes, while holding TEST for five seconds forces a defrost that stays until TEST is pressed again — with the manual warning that left too long, forced defrost will trip the unit on high pressure, and that repeated defrost tests can themselves log a '3' short-cycling fault (the compressor did not run three minutes for three consecutive calls), cleared by removing low-voltage power from the outdoor board. For owners, the documented numbers calibrate expectations: a defrost every 34-plus minutes in hard frost is the algorithm's floor, 14 minutes is its ceiling, 'd' on the display is the whole event in one letter, and a unit defrosting far more often than the 34-minute minimum allows is describing a sensor or charge problem, not enthusiasm.
Active protection: why Rheem's L-codes refuse to reset themselves, and what EcoNet adds to the story
Rheem's ICC divides its reports into two moral categories. Ordinary trips — 21 (low pressure control open), 29 (high pressure control open), the protector trip P — are information: the control saw a protection device open and said so. But the same event three times in a single call changes category. Three LPC opens in cooling lock the compressor out under flashing L21; in heating, three opens within 120 minutes produce the hard-lockout form, and the manual repeats the same sentence under each of these modes: this mode of active protection must be manually reset. The compressor start/run family escalates identically — open start circuit 06 becomes L6 at four occurrences in a call, open run 07 becomes L7, and four consecutive protector trips averaging under 15 seconds become L4, locked rotor. The design philosophy is consistent and worth stating to owners plainly: Rheem will let a transient clear itself, but a fault that repeats inside one demand is treated as a condition, and conditions require a human decision — power removed and restored after the cause is addressed — rather than a timer's forgiveness. The cause lists in the manual keep the human's search short: for 21, low charge, a frozen coil on whichever side is cold, a blower not running, or an expansion valve misbehaving; for 29, a dirty coil or dead fan outdoors in cooling, a dirty filter/coil or stopped blower indoors in heating, a liquid-line restriction, or overcharge. On EcoNet variable-speed systems the same events wear a second name at the wall control: the manual pairs display codes with A/T alert numbers — under-voltage 27 with A907, over-voltage 28 with A906, the high-pressure event with A/T923, ambient sensor fault 84 with T952, configuration failure 93 with A950 — and the control holds the compressor off until conditions genuinely normalise (after a 28, for instance, it restarts only when input voltage falls back to 252 VAC or below). That dual naming is why a Rheem service call should always quote both numbers exactly as each device showed them: the board's two digits and the EcoNet alert are two indexes into the same manual, and the pair identifies the event faster than either alone. What neither display will do is absolve the underlying physics — a unit can be reset out of L29 in ten seconds and be back in it within the hour if the coil is still matted with dirt, because the control counts events, not intentions. Like its furnace sibling, the ICC also keeps a written diary: the control stores the last six fault codes, and a technician recalls them in the test/fault-recall mode — most recent first, with a fault that repeated consecutively able to occupy up to three of the six slots — and clears the history by holding the button longer. For a homeowner that diary matters most after intermittent faults: the 21 that appeared once during a storm-week icing event and then vanished is still recorded, and it converts a 'no fault found' visit into a conversation about charge and coil condition. Rheem's design throughout is conservative in the same direction — displays for everything, forgiveness for transients, amnesia for nothing, and a locked door, the manually reset L-code, in front of every fault that has already repeated itself three times.
Less common and model-specific codes
Search data shows owners also meet these codes on Rheem heat pumps: 31, L15, L16, L17, L18, L32, L36, L42, L8. They are not part of the core code list Rheem publishes for most models — several are series-specific, abbreviated display readings, or codes carried over from a sister platform — so we do not publish meanings for them rather than guess. Treat them by symptom: note what the machine was doing when the code appeared (filling, draining, heating, spinning), run one full power cycle (5 minutes off), and if the code returns, match the symptom to the closest documented family in the table above and check the tech sheet stored inside your machine for the model-specific definition.
Related guides
Facts on this page were checked against manufacturer documentation: www.manualowl.com · pts.myrheem.com · www.212hvac.com