Water Heaters

ECO high-limit tripped

Tank water exceeded about 185°F and the high-limit safety opened.

Power anode fault

No power to the powered anode (16) or anode circuit failure (17).

Normal: pilot lit, control OK

A single blink repeating about every three seconds is the normal heartbeat: the pilot is proven and the gas control is working. It is not a fault.

Low thermopile voltage

The pilot is lit, but the thermopile is not delivering enough millivolts for the control to open the main burner valve.

Over-temperature shutdown (ECO)

The control sensed tank water above its safe limit and locked the burner off. The energy cut-off inside the control has acted.

Sensor failure

The gas control has detected a failure of its internal temperature sensor and will not run the burner.

Gas control failure

The gas control has diagnosed an internal failure of its own valve or electronics.

Knob OFF but thermopile still producing (possible stuck pilot valve)

The control knob is in the OFF position, yet the thermopile is still generating power. Either it has not cooled down yet, or the pilot is still burning because the pilot valve did not close.

Control not powered: pilot out

The control is powered only by the thermopile, so with no pilot flame the status light stays dark. A dark LED normally means the pilot is not lit.

Control turned OFF, thermopile cooling

The heater was running and the control knob has been turned OFF. The light stays on while the thermopile cools; this is not a fault by itself.

Standby: pilot lit, burner off

Normal standby. The pilot is proven and the tank is satisfied, so the main burner is off.

Heating: main burner on

Normal call for heat. The main valve is open and the burner is lit.

Low thermopile voltage

The pilot is on but the thermopile output is too low, so the control will not open the main valve.

Temperature cut-out limit reached

Tank temperature went past the safety limit and the control shut down the burner. On some control versions a reset is required.

Temperature sensor / electronics fault

The control has detected a fault with its water temperature sensor or its own electronics and will not fire.

Door/chamber temperature sensor failure

The combustion chamber door sensor reports a fault.

Tank leak detected

The accessory module detected water.

Insufficient combustion air

Abnormal chamber temperature profile; airflow is restricted.

Control in OFF mode

Not a fault: the setpoint was recently turned to OFF and the control is waiting for the thermopile to cool.

Ignition failure

The unit tried to light but no flame was detected.

False flame detected

The control sensed a flame when none should be present.

Flame loss during operation

The flame went out while the unit was heating.

Overheating

The unit sensed an overheat condition; reported causes are restricted flow or venting problems.

Exhaust overheat

Exhaust temperature went too high.

Circuit board (PCB) abnormal

The main board reported abnormal operation.

Combustion / exhaust problem

Combustion is abnormal and the unit reduced power; often linked to exhaust or burner condition. Troubleshot like code 90.

Ignition failure

The unit could not light the burner. One of the three needed elements (gas, air, spark) is missing.

Flame loss / weak flame

The burner lit but the flame was lost or too weak during operation.

Outlet temperature spike (often scale)

Outlet water temperature rose sharply. Scale in the heat exchanger is the usual cause, because it makes the burner work harder.

Condensate drain problem

Condensate is not draining (neutralizer or drain line blocked), and the unit stopped to keep the burner from flooding.

Circuit board setting error

The board's settings are invalid, typically after a DIP switch or jumper was changed with power on, or a programming problem.

Combustion abnormality

The air-fuel mixture is wrong. The unit has detected abnormal combustion.

Dry-fire protection

The tank seems not fully filled; the heater locks itself out.

Upper element / relay circuit problem

Reported in the field as an upper element, relay or board issue; heater runs short of hot water.

No ignition

Ignition failed at startup. Gas supply is a common cause.

Flame failure / gas supply problem

Flame was lost during operation or gas supply is inadequate.

Overheating

Thermal protection tripped; the heater got too hot.

Inlet thermistor fault

The inlet water thermistor is open or faulty.

Outlet thermistor fault

The outlet water thermistor is open or faulty.

Combustion fan fault

The blower speed is abnormal or the fan failed.

Water flow control fault

The water volume control valve/motor is not working.

Scale (lime) buildup

The heat exchanger needs descaling.

No burner operation during freeze protection

The unit wanted to fire in freeze-protection mode but the burner did not operate.

Air supply or exhaust blockage

The unit sensed a restriction in combustion air intake or exhaust venting and shut down.

No ignition

The burner did not light during the ignition attempt.

Flame failure

The burner lit but the flame was lost or not proven during operation.

Thermal fuse open (overheat)

A thermal fuse opened because the heat exchanger or burner area got too hot. The unit will not run until the cause is fixed and the fuse is addressed.

Over-temperature warning

Outlet water got hotter than the control allows and the unit shut down as a safety measure.

Electrical ground / short

A short to ground was detected in a component or harness, often right after water flow starts.

Condensate trap full

The condensate trap/drain is not draining and the unit has stopped to avoid flooding the burner.

Flammable vapor sensor

The flammable vapor sensor tripped or its circuit is faulty (models with the sensor).

Outlet water temperature sensor fault

The outgoing water temperature sensor reads out of range (open or shorted).

Combustion air temperature sensor

The air temperature thermistor (fan housing) reads out of range.

Exhaust gas temperature sensor

The exhaust temperature sensor reads out of range (condensing models).

Outdoor / freeze-protection sensor

The outdoor-air (freeze protection) thermistor is open or shorted. Some series still fire and flash 41 with the set point; others will not fire.

Inlet water thermistor

The inlet water thermistor is open or disconnected; the heater may keep running and flash 51.

High exhaust gas temperature

Exhaust temperature stayed above its limit (around 163°F on the documented models), so the heater cut firing then shut down.

Burner bi-metal open

One of the overheat bi-metal switches on the burner assembly opened. Needs the cause fixed, then a power reset.

Secondary heat exchanger bi-metal open

A bi-metal on the secondary (condensing) heat exchanger opened.

Combustion fan fault

The combustion fan is not running at the speed the control expects.

Recirculation / pump circuit problem

On pump/recirculation models: air in the loop, a plumbing leak, or wrong recirculation settings.

Water flow control fault

The water flow control valve is not operating correctly.

PC board fault

The controller found an internal or parameter fault.

Flame sensing (flame rod) fault

The flame rod circuit is faulty.

Water leak detected

The unit's leak sensor detected water inside the cabinet.

Maintenance performed (history marker)

A record in the code history showing that maintenance was performed; not an active fault.

Scale build-up in heat exchanger

The control estimates that lime scale is building up in the heat exchanger and is asking for a flush/descale.

Cascade secondary unit error

Commercial cascade: the primary display flashes SE when a secondary heater has a code.

Service reminder

Time-based service indicator set at installation; the heat exchanger is due for service (e.g., descaling).

Abnormal combustion warning

Combustion is abnormal (warning before 991).

Ignition failure

Burner did not light.

Flame loss

Flame went out during operation.

Outlet thermistor failure

Outlet water thermistor is open or shorted.

Inlet thermistor failure

Inlet water thermistor is open or shorted.

Mixing thermistor failure

Mixing (bypass) thermistor is open or shorted.

Air-fuel ratio rod failure

The air-fuel ratio rod signal is abnormal.

Flow sensor failure

Flow sensor fault (Easy-Link / Multi-Link systems).

Gas solenoid valve failure

A gas solenoid valve is abnormal.

Fan motor fault

Combustion fan motor is abnormal.

Computer board failure

The control board detected an internal fault.

False flame detected

Flame signal seen when none should exist.

Remote controller communication failure

Water heater and remote are not communicating.

Improper combustion

Combustion is unsafe; carbon monoxide risk.