Troubleshooting

Rinnai RU199iN Error Codes

An independent, quick-reference guide to resolve gas heater error codes, descaling alerts, and venting issues.

GAS & VENTING SAFETY WARNING

The Rinnai RU199iN is a high-output **gas condensing appliance**. If you smell gas, immediately shut off the manual gas control valve, evacuate the building, and call your gas provider or emergency services. For electrical work (like swapping the controller or PC board), disconnect the 120V power cord before proceeding.

Quick Reference Index

Error Code / Fault Status / LED Severity Quick Meaning Action
Code 10 Flashing 10 (Controller) Warning Air flow or venting blockage. Exhaust or intake pipes are obstructed. View Fix ↓
Code 11 Flashing 11 (Controller) Danger Ignition failure. The burner could not ignite due to gas supply or spark issues. View Fix ↓
Code 12 Flashing 12 (Controller) Danger Flame failure. The flame was established but went out during heating. View Fix ↓
Code 14 Flashing 14 (Controller) Danger Thermal fuse or overheat switch triggered. Unit shell is running too hot. View Fix ↓
Code 25 Flashing 25 (Controller) Warning Condensate trap is full or drain line is clogged/frozen. View Fix ↓
Code 79 Flashing 79 (Controller) Danger Water leak detected inside the chassis pan. View Fix ↓
Code LC (or 00) Flashing LC / LC0 / LC2 Warning Scale buildup inside the heat exchanger. Service flushing is required. View Fix ↓

Detailed Troubleshooting Steps

Code 10

Venting or Air Flow Blockage

Warning

What it means: The fan speed or pressure sensor indicates that the exhaust flue or air intake pipe is restricted, preventing correct exhaust venting.

Common Causes:
  • Bird nests, leaves, ice, or snow blocking the outdoor termination hood.
  • Venting pipe lengths exceed maximum limits specified in installation guidelines.
  • Blocked flue outlet collar or loose fan connector plug.
How to Rectify:
  1. Inspect the external vent terminal hoods. Clear any debris or obstructions.
  2. Ensure the venting system is constructed from approved PVC/CPVC schedule 40 pipes.
  3. Check the combustion fan connection inside the unit and clean fan blades if dirty.
Code 11

Ignition Failure

Danger

What it means: The burner fails to ignite after multiple attempts. The controller detects no flame current.

Common Causes:
  • Manual gas valve is closed or gas line has air trapped in it.
  • Dirty or corroded spark igniter rod.
  • Faulty gas control valve or wiring.
How to Rectify:
  1. Confirm that the gas valves at the meter and unit are fully turned on.
  2. Turn off power, remove cover, and clean carbon deposits off the igniter tip using fine steel wool.
  3. Verify the igniter wire is securely attached. If it sparks but won't catch, check gas pressure.
Code 12

Flame Failure

Danger

What it means: Flame is established but goes out. The safety flame rod sensor detects loss of current during operation.

Common Causes:
  • Low gas supply pressure (often occurs when other gas appliances turn on).
  • Poor ground connection between the burner plate and control board.
  • Corroded flame sensor rod.
How to Rectify:
  1. Confirm dynamic gas supply pressure under maximum load (should be 3.5"-10.5" W.C. for Natural Gas).
  2. Inspect and clean the flame sensor rod located on the burner window cover.
  3. Ensure the unit casing is correctly grounded to electrical earth.
Code 14

Thermal Fuse / Overheat Switch

Danger

What it means: The thermal fuse wrapped around the copper heat exchanger heat shields has burned/opened due to extremely high heat.

Common Causes:
  • Mineral scale buildup inside the tubes causing hot spots on the exchanger walls.
  • Low water flow coupled with blocked high-fire burner.
  • Crack or leak spraying hot water onto the exterior shell.
How to Rectify:
  1. Turn off power and check the copper exchanger body for discoloration or cracks.
  2. Measure continuity across the thermal fuse connectors. If open, the fuse must be replaced.
  3. Flush the system using descaling solution to prevent future heat spots.
Code 25

Condensate Drain Blockage

Warning

What it means: The internal condensate level sensor detects that the drain pan is flooded, threatening to short-circuit internal components.

Common Causes:
  • Condensate drain line is pinched, kinked, or clogged.
  • Outdoor drain tube end frozen shut during winter.
  • Failed condensate neutralizer cartridge backing up fluid.
How to Rectify:
  1. Check the plastic drain pipe running from the bottom of the heater. Ensure it flows freely.
  2. Flush the internal condensate trap with fresh water to clear internal sediment.
  3. Inspect outdoor discharge lines for ice blockages.
Code 79

Water Leak Detected

Danger

What it means: The leak detection sensor contacts in the bottom chassis pan have detected liquid water, indicating an internal plumbing leak.

Common Causes:
  • Cracked pipe connections, heat exchanger, or leaking O-rings.
  • Condensate trap collection cup cracked or overflowing.
  • External water dripping onto the top venting connection down into the casing.
How to Rectify:
  1. Shut off cold water supply valve immediately. Disconnect power.
  2. Dry out the bottom casing tray thoroughly.
  3. Turn on water supply slowly while inspecting the burner, water valves, and pipe unions to identify the leak location and replace damaged gaskets/parts.
Code LC

Scale Buildup Warning

Warning

What it means: The controller detects that the temperature difference across the heat exchanger is too wide, indicating thick mineral scale buildup. Service flushing is required.

Common Causes:
  • Hard water running through the unit without a softener.
  • Heater has been in service for more than 12 months without a descale flush.
How to Rectify:
  1. Perform a full descale flush. Connect a recirculation pump and circulate food-grade vinegar or citric acid solution through the isolation valves for 45-60 minutes.
  2. Clear the warning code: press the key buttons on the digital controller to reset the alert (detailed descaling guides cover the key press sequence).