Why does my Rheem gas water heater show Error Code 00 and the recirculation pump is always on?

Error Code 00 indicates continuous combustion for over an hour, often caused by a constantly active recirculation pump that simulates water draw.

How can I tell if my Rheem water heater's recirculation pump is causing Error Code 00?

If the pump is always running, the pipes are hot, and the appliance turns on without water draw, this is the probable cause. A technician will disconnect it for verification.

What should I do if my Rheem water heater shows Error Code 00 and the recirculation pump is always on?

Contact a qualified technician immediately. DIY on gas appliances is forbidden and dangerous. A professional will safely resolve the fault.

Rheem Gas Water Heater Error Code 00: Diagnosis and Solution

⚠️ SAFETY WARNING / SERIOUS RISK. This appliance operates with critically dangerous components (High Voltage or Gas). DIY repair of critical devices can be fatal and is prohibited by law. Physical intervention legally requires qualified specialized technicians to issue compliant safety certificates. This diagnosis is provided EXCLUSIVELY for educational and informational purposes.

IF the recirculation pump is continuously active (50% probability)

Key signs/indicators:

The external or integrated recirculation pump runs continuously, even when there is no demand for hot water.
The return pipes of the recirculation loop are constantly hot.
The Rheem water heater cycles on and off or stays on for long periods without apparent water draw.

Quick checks (reserved for qualified technicians):

Pump disconnection: Temporarily cut off the electrical supply to the recirculation pump. If the water heater stops continuous combustion and Error Code 00 disappears after reset, the pump is almost certainly the cause.
Logic control: Check the configuration of the timer or thermostat that controls the pump. Often, an "always on" setting or a control failure causes this behavior.

THEN: The problem is related to the domestic hot water recirculation pump. This, by operating continuously, simulates a constant water draw. The Rheem electronic board, detecting an uninterrupted flow for over 60 minutes, activates safety Code 00 to prevent overheating and waste. This often happens when the pump is not managed by a return thermostat or an adequate timer.

Output for technician: "The Rheem appliance displays Code 00. It has been observed that the recirculation pump remains permanently active. Verification of the pump's control logic (return thermostat or timer) is required, and if necessary, its replacement or reprogramming." Hot water recirculation pump on eBay

IF the water heater turns on or attempts to turn on without water draw (30-45% probability)

Key signs/indicators:

The burner activates even if all hot water taps are closed.
The sound of water flow is heard inside the water heater even without opening taps.
The main water meter records a constant minimum consumption, even with all draw points closed.

Quick checks (reserved for qualified technicians):

Flow sensor inspection: Disconnect the appliance from power. Disassemble the flow sensor and check the free rotation of the internal magnetic turbine. Clean any limescale deposits or debris that might block it.
Flow sensor electrical test: With a Professional digital multimeter on eBay, measure the voltage on the flow sensor's signal cable. At zero flow, there should be no frequency oscillations or anomalous continuous voltages that simulate a flow.
System leak check: Close the cold water inlet valve to the water heater. If the burner turns off immediately and does not restart, the problem is caused by a downstream water leak or a dripping/partially open tap.

THEN: The most probable cause is a blocked or faulty flow sensor (30%), or a hidden water leak on the hot water line (15%).

Flow sensor: If the sensor's impeller is blocked by limescale or debris, it sends a constant flow signal to the board, keeping the burner active. This is a typical error after years of operation.
Hidden leak: Even a constant micro-leak in the plumbing system, if it exceeds the water heater's minimum activation flow rate (typically 1.5-2.5 L/min), will keep it on, leading to error 00.

Output for technician: "The Rheem appliance displays Code 00, turning on even without water draw. Verification of the Rheem water flow switch on eBay is required to rule out a fictitious flow signal (blocked turbine or short circuit). In parallel, perform a leak test on the plumbing system to rule out micro-leaks on the hot water line." A wash with Descaling liquid anti-limescale on eBay might be useful to remove deposits.

IF previous checks do not resolve or if the gas valve remains open (5% probability)

Key signs/indicators:

The gas valve remains powered and open even when the control board does not require combustion and the flow sensor has been ruled out.
There is no evidence of problems with the recirculation pump, flow sensor, or water leaks.

Quick checks (reserved for qualified technicians):

Visual PCB inspection: Check for the absence of burns, bulging capacitors, or signs of overheating on the gas valve control relays on the main electronic board.
Gas valve voltage measurement: Measure the voltage across the gas valve coil after disconnecting the flow sensor connector. If the valve remains powered, it indicates a PCB fault.

THEN: This scenario, though rare, suggests a fault in the main electronic board (PCB). A gas valve control relay might have become "stuck" in the closed position, keeping the burner active regardless of other sensors. The internal logic of the PCB might also misinterpret sensor signals, leading to Code 00.

Output for technician: "The Rheem appliance displays Code 00. After ruling out anomalies in the recirculation pump, flow sensor, and water leaks, a fault in the main electronic board (PCB) is suspected. Verification of the gas valve control relays and general integrity of the PCB is required."

CONCLUSION

For an accurate assessment and resolution of Code 00 on your Rheem water heater, here are the operational decisions based on probability:

Contact a qualified technician IMMEDIATELY: The most probable cause (50%) is a problem with the recirculation pump. A technician can easily diagnose it by temporarily disconnecting it and checking its configuration or fault. Given the nature of the device (gas), DIY intervention is prohibited and dangerous.
Technician for in-depth diagnosis: If the recirculation pump is not the cause, the technician will proceed with checking the flow sensor (30% probability) and the plumbing system for hidden leaks (15% probability). Both require specific skills and tools.
Device replacement: If the technician diagnoses a fault in the main electronic board (5% probability), repair might be uneconomical compared to the cost of a new water heater, especially if the appliance is old. The technician will provide you with a quote for PCB replacement or advise you to replace the entire unit.

When the Rheem water heater's flow sensor gets blocked due to limescale deposits, the internal turbine cannot return to its resting position. This issue causes the electronic board to detect a non-existent water flow, keeping the burner active until the safety lockout.

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