Rinnai Tankless Error Codes: What the Common Codes Mean
By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the maker’s manual 
LC means scale is building up and the heater needs flushing, and it is the only code that keeps running. 11 is no ignition, usually gas or air in the line. 12 is flame failure, 10 is a blocked vent, and 25 is a condensate backup. Rinnai's own manual lists a fix for each, and many need nothing more than the gas turned on or the filter cleaned.
A Rinnai tankless water heater checks itself all the time, and when something is wrong it flashes a two character code on the temperature controller. Many of those codes have a fix you can do yourself in a few minutes.
Everything on this page comes from Rinnai’s own documents: the installation and operation manual for the VB series indoor heaters, and Rinnai’s longer guide for technicians, Troubleshooting Tankless Water Heater Diagnostic Codes.
Before you start
What to carry: a torch and a pen. Ten minutes for most codes.
Gas or electric? These are codes for Rinnai gas tankless heaters. Electric tankless heaters from other makers use their own codes.
Write the code down before you reset anything. Rinnai asks for it when you call for service, and a reset can hide what the heater was trying to tell you.
Code 65 during a bath fill: turn the water off now. Rinnai says the valve failed to close, and to turn off the water immediately and stop the bath fill.
Rinnai’s own warning on this table: call a technician for any remedy that involves gas or electricity, or if you have any doubt about doing it yourself. The owner’s fixes below are the ones that involve neither.
How to see and clear the codes
Read the code, then read the history
The current code flashes on the temperature controller in place of the temperature.
The last nine codes. On the standard controller, Rinnai says to press and hold the On/Off button for two seconds, then press the up button while still holding it. The last nine codes flash one after another. Do the same again to leave.
Clearing a code. For code 03, Rinnai says to turn off all hot taps and press On/Off twice. Many codes clear the same way once the cause is fixed.
LC is different. It is the only code that lets the heater keep running, the display alternates LC with the temperature, and the controller keeps beeping. On older models it clears if the power is turned off and on, but that only hides it. On newer ones Rinnai’s guide says LC locks the heater out, and pressing On/Off five times runs it for another 70 hours. The fix is a flush.
The codes an owner can often fix
Work Rinnai's first check for your code
LC, or 00 in the history: scale in the heat exchanger. Hard water leaves lime inside, and Rinnai says it must be flushed or the heat exchanger is damaged: how a tankless heater is flushed.
11: no ignition. Rinnai’s first check is that the gas is on at the heater and the meter, or that a propane tank is not empty. After any gas work, air in the line causes this too.
12: flame failure. The flame lit and went out. Rinnai starts with the gas being on, then obstructions in the flue outlet, then the flame rod.
10: air supply or exhaust blockage. Check nothing is blocking the air intake or the exhaust outside: a nest, leaves, snow, or something stacked against the terminal.
25: condensate backed up. On condensing models, Rinnai’s guide says code 25 appears when condensate backs up and trips the float switch, or when the condensate pump stops.
No code, and nothing happens when you open a tap. Rinnai’s list starts with cleaning the inlet water filter and making sure the tap is open far enough to reach the minimum flow the heater needs to fire.
The common codes
| Code | What Rinnai calls it | Who fixes it |
|---|---|---|
| LC or 00 | Scale build up in the heat exchanger | Owner, a flush |
| 02 | No burner operation during freeze protection | Service call |
| 03 | Power interruption during bath fill | Owner, taps off, On/Off twice |
| 10 | Air supply or exhaust blockage | Owner first, then installer |
| 11 | No ignition | Owner first: is the gas on |
| 12 | Flame failure | Owner first: gas, flue outlet |
| 14 | Thermal fuse | Technician |
| 16 | Over temperature warning | Airflow and flow first, then technician |
| 25 | Condensate backed up, float switch | Owner first: drain and pump |
| 31, 73 | Burner sensor error | Technician |
| 32, 33, 34 | Water, heat exchanger or air temperature sensor | Technician |
| 52 | Modulating gas valve signal | Technician |
| 54 | High exhaust gas temperature | Technician |
| 57, 58 | A heat safety switch on the burner or heat exchanger opened | Technician |
| 61 | Combustion fan failure | Technician |
| 63 | Recirculation settings or bypass | Installer |
| 65 | Water flow control fault in bath fill | Water off now, then technician |
| 71 | Gas valve circuit fault | Technician, control board |
| 72 | Flame sensing device fault | Technician, flame rod |
| 79 | Leak detector | Look for water inside the unit, then technician |
| SS | Time for service | Book a flush and service |
| FF | Marker that service was done | Not a fault |
When it needs a technician
Know when to stop
Anything that involves the gas valve, the board or a sensor. Codes 14, 31 to 34, 52, 54, 57, 58, 61, 71, 72 and 73 all need a meter and parts.
11 or 12 that come back with the gas definitely on. Rinnai’s list moves on to gas pressure, line sizing, the igniter and the burners. That is technician work.
16 that repeats. Over temperature with good airflow and flow points at a clogged heat exchanger or a circulation problem.
79. The leak detector has found water inside the cabinet. Turn the water off to the heater until it is looked at.
Anything that clears and returns. The cheap cause was not the real one.
Questions people ask
How often does a Rinnai need flushing?
It depends on the water. Rinnai’s manual gives water quality limits, with hardness up to 200 mg per litre. Harder water than that scales faster, and LC is the heater asking. Once a year is a sensible habit on hard water.
My Rinnai shows 11 after the gas was turned off for work.
Air in the gas line. Rinnai lists bleeding the air as one of the fixes for code 11, and it can take a few tries before gas reaches the burner.
White smoke is coming out of the vent.
Rinnai says that is condensed water vapour in cold weather, not smoke. It is normal.
The fan keeps running after I turn the tap off.
Also normal. Rinnai says the fan runs on for a short time to keep temperatures steady and clear the last of the exhaust.
Hot water goes cold when I turn the tap down.
You have probably dropped below the minimum flow the heater needs to stay lit. Open the tap a little more, or clean the inlet filter: the minimum flow every tankless heater needs.
My code is not on this list.
Newer SENSEI and commercial models add codes of their own. The Technical Data Sheet inside the heater’s front cover lists every code for your model.
Sources: Rinnai VB Series installation and operation manual, and Rinnai's Troubleshooting Tankless Water Heater Diagnostic Codes guide
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