Rinnai Tankless Water Heater Certified Service

Error Code 11 indicates ‘No Ignition’. The unit is trying to light but cannot. This can be caused by no gas supply, insufficient gas pressure, or a dirty igniter/flame rod. Verify your gas is on. If it is, a technician needs to clean the ignition components and check gas pressures.

Error Code 12 is ‘Flame Failure’. The unit lit briefly but the flame went out. Often caused by low gas pressure, a blocked intake filter, or a dirty flame rod. It requires professional diagnosis to check gas pressures and venting — don’t ignore it.

LC stands for ‘Lime Condition’ — scale buildup. Your heat exchanger is accumulating minerals, reducing efficiency and risking damage. You need to descale immediately to clear the minerals and reset the code. Book a flush before it causes failure.

Rinnai recommends annual maintenance including inline filter cleaning, air intake filter check, and a full heat exchanger descaling flush. In very hard water areas (Marin County water is notably hard), a 6-9 month flush interval may be warranted.

Code 10 is ‘Air Supply or Exhaust Blockage.’ The unit detects restricted airflow through the intake or exhaust venting. Common causes include a bird nest or debris in the vent termination, a kinked or sagging vent pipe, or condensation frozen inside the exhaust in cold weather. Visually inspect your vent terminations outside the house first. If they’re clear, a technician needs to check the full vent run for blockages or improper slope.

Code 14 is a ‘Thermal Fuse’ trip — a serious safety shutdown. The internal thermal fuse activated because the unit reached dangerously high temperatures. This is almost always caused by inadequate venting, a blocked exhaust, or a failed fan motor. Do not attempt to reset this yourself. The thermal fuse is a one-time safety device that must be replaced by a technician after the root cause is resolved. Call for service immediately.

Code 25 indicates ‘Condensate Overflow.’ The condensate drain system is backed up and the unit can’t safely expel the acidic condensate produced during combustion. Check if the drain line is kinked, frozen, or clogged. The condensate neutralizer cartridge may also be exhausted and blocking flow. Annual maintenance includes flushing the condensate system and replacing neutralizer media.