On the covered Rinnai tankless water heater, 14 means heat exchanger overheat. First, turn the water heater's power off and let it cool before a single reset; do not keep resetting. Then: Rinnai directs measuring the resistance of the overheat switch, checking the heat exchanger surface for hot spots that indicate blockage from scale, and flushing the heat exchanger per the manual. Rinnai stresses that hard water must be treated to prevent scale build-up or damage. It also says to make sure the unit is not forced to a Hi setting.
Differential
Likely causes of “Rinnai tankless water heater code 14”, and how to tell them apart
- 1
Scale blocking the heat exchanger
What separates it Hot spots and overheating
How to confirm Flush the heat exchanger as the manual describes
- 2
Hard water
What separates it Scale builds quickly
How to confirm Treat or soften the water
- 3
The unit forced to a high setting
What separates it The heater works at the limit
How to confirm Do not force a Hi setting
- 4
A failing overheat switch
What separates it The resistance is out of range
How to confirm Technician measures it
- 5
Low water flow
What separates it The exchanger heats without enough water
How to confirm Check the inlet filter and flow
Before you touch a setting
Record this first — changing settings destroys the evidence
- The set temperature
- Whether flow is weak
Try in this order
0 of 8 completedWhat to do first
ReversibleTurn the water heater's power off and let it cool before a single reset; do not keep resetting.
Correct only the documented fault domain
ReversibleRinnai directs measuring the resistance of the overheat switch, checking the heat exchanger surface for hot spots that indicate blockage from scale, and flushing the heat exchanger per the manual. Rinnai stresses that hard water must be treated to prevent scale build-up or damage. It also says to make sure the unit is not forced to a Hi setting.
Turn the power off
ReversibleLet it cool.
Reset once
ReversibleThen run a hot tap.
Check the inlet filter
ReversibleFor debris.
Check the set temperature
ReversibleNot forced high.
Arrange a flush
ReversibleIf scale is likely.
Call a technician
ReversibleIf it returns.
Model-specific
What is true of this model and not of its siblings
- Scale and heat
- Scale is a poor conductor, so a scaled heat exchanger overheats in places while the water takes less heat. Rinnai stresses that hard water must be treated to prevent scale build-up or damage.
- Rinnai's checks
- The company directs measuring the resistance of the overheat switch, checking the surface for hot spots that point to a blockage, flushing the exchanger and making sure the unit is not forced to a Hi setting.
- Safety
- An overheating gas appliance should be left to cool and checked by a technician before it is used again.
Stop boundary
When this stops being a self-service repair
- !Turn the power off and let the unit cool before a single reset
- !Do not keep resetting
- !Call a technician if it returns
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 14 mean on a Rinnai tankless water heater?+
Heat exchanger overheat.
What causes it?+
Often scale.
Should I keep resetting?+
No, let it cool.
How do I prevent it?+
Flush yearly and treat hard water.