On the covered Rheem tankless gas water heater, 1L means warning: the water heater has a buildup of lime deposits. Rheem's pocket manual says the control board detected lime build-up inside the heat exchanger, and the unit must be drained and flushed to prevent permanent damage. First, note whether hot water is still being delivered.
Differential
Likely causes of “Rheem tankless gas water heater code 1L”, and how to tell them apart
- 1
Lime and scale inside the heat exchanger
What separates it The control board detects the build-up
How to confirm Drain and flush the unit
- 2
Hard water
What separates it Scale returns quickly
How to confirm Install a softener or scale filter
- 3
A flush not done for years
What separates it The warning appears
How to confirm Arrange a flush
- 4
Excessive scale
What separates it The first flush is not enough
How to confirm Repeat the flush
- 5
Reduced flow
What separates it Hot water output drops
How to confirm Flush and clean the inlet filter
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether hot water is still delivered
- When it was last flushed
Try in this order
0 of 8 completedWhat to do first
ReversibleNote whether hot water is still being delivered.
Correct only the documented fault domain
ReversibleRheem's use and care chart says to contact a dealer or qualified service technician. The pocket manual says the flush may need repeating for excessive lime and scale, and that the 1L code is reset by holding the MIN and MAX buttons together for 10 seconds. It describes the flush with a submersible pump from the Rheem/Ruud Tankless Flush Kit. Rheem's steps when a code shows: turn on a hot water faucet and recheck the remote control display. If the code stays, turn off the faucet and the water heater, unplug the water heater for about 30 seconds and plug it back in, follow the chart for your code, restart the water heater and recheck.
If the code is still shown, turn off the faucet and the water heater, note the code and call for service. If a code is not in the chart, turn the water heater off immediately and call for service.
Note whether hot water still works
ReversibleIt may.
Arrange a flush
ReversibleBy a technician or with the flush kit.
Repeat if needed
ReversibleFor heavy scale.
Reset the code
ReversibleHold MIN and MAX for ten seconds.
Fit a softener or scale filter
ReversibleIf your water is hard.
Schedule yearly flushes
ReversibleTo prevent a repeat.
Model-specific
What is true of this model and not of its siblings
- Why lime matters
- Lime scale on the heat exchanger acts as an insulator and narrows the water passages, so the unit works harder, runs hotter and eventually fails. The 1L code warns before that happens.
- Rheem's guidance
- Rheem's manuals say the unit must be drained and flushed to prevent permanent damage, that a flush may need repeating for excessive lime and scale, and that the flush uses a submersible pump from its Tankless Flush Kit.
- Prevention
- A yearly flush, a clean inlet filter and a softener or scale inhibitor in hard water areas keep the heat exchanger clear.
- What the warning protects
- Lime scale narrows the water passages and insulates the heat exchanger, so a scaled unit runs hotter and wastes gas. The 1L warning arrives while hot water still works, to give you time to flush before damage occurs.
- Doing the flush
- Rheem's flush uses a submersible pump, a bucket and a descaling solution circulated through the unit for some time, followed by a rinse. A flush kit has the hoses and fittings. A technician can do it in under an hour.
- After the flush
- Reset the code by holding the MIN and MAX buttons together for ten seconds. If the code returns soon, the scale was heavy and a second flush may be needed. A softener or scale inhibitor stops it recurring.
Stop boundary
When this stops being a self-service repair
- !Rheem's chart says to contact a dealer or qualified service technician
- !Do not ignore it; it can damage the unit
- !Hold MIN and MAX for ten seconds to reset after the flush
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 1L mean on a Rheem tankless gas water heater?+
Warning: the water heater has a buildup of lime deposits. Rheem's pocket manual says the control board detected lime build-up inside the heat exchanger, and the unit must be drained and flushed to prevent permanent damage.
What does code 1L mean on a Rheem tankless?+
The control detected lime build-up in the heat exchanger.
Is it urgent?+
Rheem says to flush to prevent permanent damage.
What do I need to flush it?+
A submersible pump and the flush kit.