Rinnai tankless water heater error codes

27 codes that Rinnai publishes for its tankless water heaters, each with what it means, the likely cause, what you can safely check and when to call a licensed professional. Tap your code:

If you smell gas

Stop: do not reset, relight or check anything on this page. Rinnai’s own words, from the manual’s front warning (page 2) and its operating label (page 68):

Do not try to light any appliance.
Do not touch any electrical switch; do not use any phone in your building.
Immediately call your gas supplier from a neighbor’s phone. Follow the gas supplier’s instructions.
If you cannot reach your gas supplier, call the fire department.

Calling from a neighbor’s phone means leaving the building first. Source: SENSEI Tankless Water Heater (Residential) Installation and Operation Manual, RU199i/e, RU180i/e, RU160i/e, RU130i/e (100000467), section 5.6 Diagnostic Codes, pages 73–75

Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone. Everything else is for a licensed professional — in the manuals’ words, a qualified installer, service agency or the gas supplier. If you smell gas, do none of the checks: follow the maker’s gas-smell instructions at the top of the page. Codes that need one are marked Licensed pro.

Read this first

Rinnai tankless water heaters show a two-digit diagnostic code on the controller (11, 12, 10 …) or two letters for a service reminder (SS, FF). This page follows the diagnostic-code table in the Installation and Operation Manual of Rinnai’s SENSEI residential condensing heaters (RU199, RU180, RU160 and RU130, indoor i and outdoor e models), section 5.6. Rinnai’s table mixes owner checks with checks for a trained professional and says so; this page separates them: the owner checks are the ones you can do from outside the cabinet, everything with a meter or a part number is marked for a licensed professional. To see the last nine codes the heater stored, turn it off, then press and hold On/Off for 2 seconds and press the Up button with it; do the same to leave that view.

`11` No ignition: the heater does not light

What it means: The heater tried to light the burner and could not — Rinnai’s table calls it “No Ignition (Heater Not Turning On)”. Usually you get lukewarm or cold water and the code on the controller.
Likely cause: No gas reaching the burner is the first thing Rinnai checks: a closed gas valve, an empty propane tank, air in a new gas line, or the wrong gas type or inlet pressure. Then the flame rod, igniter, gas solenoid valves, gas orifice and a blocked condensate line.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Check that the gas is turned on at the water heater, at the meter, or at the propane cylinder.
On propane, make sure there is gas in the tank.
Make sure the condensate drain line is not blocked or frozen.
When to call a licensed professional: If 11 comes back with the gas on, call a licensed professional: Rinnai’s remaining checks are the gas type and inlet pressure, bleeding air from the gas lines, the circuit-board ground wire, the flame rod, the igniter, the gas solenoid valves and the gas orifice.

Source: Rinnai, SENSEI Tankless Water Heater (Residential) Installation and Operation Manual, RU199i/e, RU180i/e, RU160i/e, RU130i/e (100000467), section 5.6 Diagnostic Codes, pages 73–75 Checked 2026-09-29.

`12` No flame: the flame went out

What it means: The burner lit, then the flame was lost while the heater was running.
Likely cause: Rinnai’s list is short: gas turned off or running out, propane tank empty, the flame rod wire, the wrong gas type or inlet pressure, and air in the gas lines.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Check that the gas is turned on at the water heater, at the meter, or at the propane cylinder.
On propane, make sure there is gas in the tank.
When to call a licensed professional: If 12 comes back with gas supplied, call a licensed professional for the gas type, inlet pressure, bleeding the gas lines and the flame rod wire.

`10` Air supply or exhaust blocked, or condensate trap full

What it means: The heater is not getting enough combustion air, cannot push out its exhaust, or its condensate trap has filled up, so it stops.
Likely cause: A blocked or frozen condensate line, a dirty air filter (indoor models), blocked air-intake or exhaust vents, vents that are too long or the wrong material, a wrong high-altitude setting, debris in the fan, or a check valve stuck between the fan casing and the burner.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Make sure the condensate drain line is not blocked or frozen.
Look at the vent ends outside: clear snow, leaves, nests or anything else blocking the air intake or the exhaust.
When to call a licensed professional: Call a licensed professional if 10 stays: the internal air filter, the vent length and materials, the altitude setting, the fan and its check valve are Rinnai’s other checks.

`17` Venturi blockage

What it means: The heater sees a blockage at the venturi, where gas and air mix before the fan.
Likely cause: Rinnai sends you to the code 10 causes first — condensate line, air filter, vents — and only then to a blocked venturi.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Do the owner checks for code 10 first: the condensate drain line, and the air-intake and exhaust vent ends outside.
When to call a licensed professional: If the code 10 checks do not clear it, Rinnai says to check the venturi and to call Rinnai’s technical department: a job for a licensed professional.

`03` Power cut during bath fill

What it means: The power went off while the heater was running its bath-fill function, and water will not flow when the power comes back.
Likely cause: An interruption of the electricity supply during a bath fill.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Turn off all hot water taps.
Press the On/Off button on the controller twice — that is Rinnai’s action for this code.
When to call a licensed professional: If 03 keeps coming back without a power cut, call a licensed professional.

`65` Water flow control did not close during bath fill

What it means: The water flow control valve failed to close while the heater was filling a bath — water may keep running.
Likely cause: A faulty water flow control valve (Rinnai’s check is its resistance).
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Turn the water off now and stop the bath-fill function — Rinnai’s own instruction.
When to call a licensed professional: Rinnai says to contact a trained and qualified professional to service the heater: a licensed professional.

`14` Heat exchanger overheat

What it means: The overheat switch on the heat exchanger has tripped. Rinnai’s troubleshooting guide says a 14 is an indication of overheating and should be taken seriously.
Likely cause: Scale built up inside the heat exchanger (hot spots on its surface show it), a faulty overheat switch, or the heater left in its forced-high setting. Hard water that is not treated keeps building scale.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: Rinnai’s checks are the overheat switch’s resistance, the heat exchanger for scale, flushing it as the manual’s section 6.3 describes, and the forced-high setting.

`SS` Service soon: flush the heat exchanger

What it means: A time-based reminder, set during installation, that it is time to flush the heat exchanger. It is not a fault, but Rinnai says failing to flush will damage the heat exchanger, and lime damage is not covered by the warranty.
Likely cause: The reminder period set by the installer has run out; hard water makes flushing more urgent.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
To clear the reminder, press the On/Off button on the controller 5 times in 5 seconds — Rinnai’s reset for SS.
Arrange the flush: section 6.3 of the manual describes it (four gallons of undiluted white vinegar pumped through the heat exchanger with the power off and the water valves closed).
When to call a licensed professional: Have the flush done by a licensed professional if the heater has no isolation valves or you are not comfortable doing it; Rinnai strongly recommends isolation valves so the heat exchanger can be flushed.

`FF` Maintenance done (history marker)

What it means: Not a fault. FF in the stored code history is a placeholder showing that a service provider carried out maintenance or service; the service provider enters it after the visit.
Likely cause: Entered deliberately after service (Up, Down and On/Off pressed together).
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Nothing to fix: FF only marks when the heater was last serviced.
When to call a licensed professional: No licensed professional needed for FF itself; if other codes sit next to it in the history, look those up.

`25` Condensate pump (accessory)

What it means: The safety switch of the add-on condensate pump has tripped: condensate is backing up, or the pump has stopped.
Likely cause: The condensate pump is off, broken, or its drain line is blocked or frozen; or its wiring to the heater is faulty.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
If you have a condensate pump, check it has power and is running, and that its reservoir is emptying.
Make sure the pump’s drain line is not blocked or frozen.
When to call a licensed professional: Call a licensed professional if the pump runs and 25 stays: its wiring and harness to the heater are Rinnai’s other check.

`54` High exhaust gas temperature

What it means: The exhaust is too hot. Rinnai’s troubleshooting guide says the heater first reduces its firing rate when the exhaust passes 163°F, then shuts down with 54 if it stays that hot for 120 seconds.
Likely cause: Blocked heat-exchanger fins, incoming water that is already too hot, or a blocked condensate line.
What you can safely check: Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
Make sure the condensate drain line is not blocked.
When to call a licensed professional: Call a licensed professional to clean the heat-exchanger fins and check the inlet water temperature; Rinnai clears the code by resetting the heater’s main power.

`05` By-pass flow control fault

What it means: The by-pass flow control device, which mixes cold water into the outlet, is not responding as it should.
Likely cause: A faulty by-pass flow control; Rinnai’s check is its resistance, then replacing the device.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: both of Rinnai’s steps are inside the cabinet.

`15` Venturi control fault

What it means: The motor that controls the venturi (the gas and air mix) is not working correctly.
Likely cause: A faulty venturi motor or gas valve assembly.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: Rinnai’s steps are checking the venturi motor, replacing the gas valve assembly and resetting the main power.

`16` High outgoing temperature

What it means: A safety shutdown because the water heater is too hot — Rinnai’s own words.
Likely cause: Rinnai points to the fan motor and the gas valve assembly.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: the fan motor and gas valve are inside the cabinet.

`19` Electrical grounding fault

What it means: A short to ground somewhere in the heater’s electrical parts.
Likely cause: A shorted component or wiring harness; Rinnai’s troubleshooting guide says the short can be in a harness, the water flow control, the by-pass valve or any part of the DC circuit.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional to find the short.

`21` Data transfer error

What it means: The circuit board’s settings were not transferred correctly.
Likely cause: Seen after the circuit board has been replaced, when the data transfer process was not completed.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call back the licensed professional who replaced the board: Rinnai says to make sure the data transfer was completed.

`32` `33` `38` `41` `51` Temperature sensor (thermistor) fault

What it means: One of the heater’s temperature sensors is reading wrong or not at all: 32 the outgoing (hot water) sensor, 33 the heat exchanger sensor, 38 the exhaust sensor, 41 the freeze-protection sensor, 51 the inlet (cold water) sensor.
Likely cause: Damaged sensor wiring, scale on the sensor, or a failed sensor.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: Rinnai’s steps are checking the wiring, measuring the sensor’s resistance, cleaning off scale and replacing the sensor.

`52` Gas valve fault

What it means: The gas solenoid valve is not working correctly.
Likely cause: Damage to the flame rod or its wire, or an open or short circuit in the gas solenoid valve.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: Rinnai says to replace the gas valve assembly and to call Rinnai’s technical department.

`61` Combustion fan fault

What it means: The fan that pushes air through the burner is not running correctly.
Likely cause: Loose or damaged fan wiring, or a fan wheel that does not spin freely.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: Rinnai’s checks are the motor harness, its resistance and the fan wheel.

`63` Recirculation low flow

What it means: On a heater set up to recirculate hot water, too little water is flowing round the loop.
Likely cause: A by-pass plug left in or filter missing (crossover mode), dirty inlet or by-pass filters, wrong recirculation settings, no pump power, or air in the recirculation line.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: the filters, parameters and pump are set inside the heater.

`70` Circuit board fault

What it means: The heater’s main circuit board has failed.
Likely cause: A faulty PC board.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: Rinnai’s action is to replace the circuit board.

`71` Solenoid valve circuit fault

What it means: The circuit that drives the gas solenoid valves reports a fault.
Likely cause: A DIP switch on the circuit board left in the ON position, a loose or damaged gas control wire, or a grounded heater circuit.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: every check is on the circuit board or its wiring.

`72` Flame rod fault

What it means: The flame rod, which senses the burner flame, reports a problem.
Likely cause: A damaged flame rod or wire, or a leaking heat exchanger.
What you can safely check: Nothing for the owner to check: this one is for a licensed professional.
When to call a licensed professional: Licensed pro Call a licensed professional: Rinnai says to check the flame rod and to verify the heat exchanger is not leaking.

A code that is not listed here

Rinnai’s own FAQ says error codes vary by product. Older non-condensing Rinnai models and the commercial and hybrid ranges use most of the same numbers, but some codes (07 on the RH180 hybrid, 30 for the flammable vapor sensor, 31, 34, 35, 57, 58, 73, 79, LC) exist only on other series and are not listed here. If nothing happens at all when you open a hot tap and there is no code, Rinnai’s table says to check you are drawing at least the minimum flow to fire the unit and to clean the inlet water filter.

We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.

Source

Every code on this page comes from these pages, published by Rinnai and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.

Rinnai: SENSEI Tankless Water Heater (Residential) Installation and Operation Manual, RU199i/e, RU180i/e, RU160i/e, RU130i/e (100000467), section 5.6 Diagnostic Codes, pages 73–75 Checked 2026-09-29.
Rinnai: Troubleshooting Tankless Water Heater Diagnostic Codes (100000652): notes on codes 14, 19 and 54, and the codes of other Rinnai series Checked 2026-09-29.
Rinnai: Rinnai FAQ: What are these error codes? Checked 2026-09-29.

Rinnai tankless water heater error codes

If you smell gas

Read this first

11 No ignition: the heater does not light

12 No flame: the flame went out

10 Air supply or exhaust blocked, or condensate trap full

17 Venturi blockage

03 Power cut during bath fill

65 Water flow control did not close during bath fill

14 Heat exchanger overheat

SS Service soon: flush the heat exchanger

FF Maintenance done (history marker)

25 Condensate pump (accessory)

54 High exhaust gas temperature

05 By-pass flow control fault

15 Venturi control fault

16 High outgoing temperature

19 Electrical grounding fault

21 Data transfer error

32 33 38 41 51 Temperature sensor (thermistor) fault

52 Gas valve fault

61 Combustion fan fault

63 Recirculation low flow

70 Circuit board fault

71 Solenoid valve circuit fault

72 Flame rod fault