Equipment error code

Rheem code 1

Code 1 — ignition failure. The control attempted to light the burner but did not detect flame within the trial period.

Equipment: water heater
Brand: Rheem
Source checked: 2026-03-01

What this code means

Code 1 — ignition failure. The control attempted to light the burner but did not detect flame within the trial period.

Source: Rheem Tankless Water Heater Use & Care Manual — Error Code Table (AP13155) · checked 2026-03-01

Which models show it

Rheem RTGH, RTG, and Performance Platinum tankless gas water heaters with digital remote error display.

What is actually happening

Hot water stops; remote or unit display shows code 1. You may hear clicking without sustained burner roar.

Is it safe to keep running?

Do not cycle hot water taps repeatedly — failed ignition attempts can accumulate gas in the chamber on some designs.

Shut it down when

Gas odor, booming ignition, or code 1 more than twice after one power cycle.

What a homeowner can safely check

Confirm other gas appliances work; check unit gas valve is on.
Verify fresh air intake and exhaust terminations are clear (tankless PVC).
Descale reminder — heavy scale can affect ignition on tankless (note for tech).
Press power button once to reset after checks — not repeatedly.

When to stop

Any gas smell indoors.
Code 1 returns immediately.
Yellow or lazy flames visible at viewport.

Likely causes ranked

1. Gas supply off or low inlet pressure
How a tech confirms: Manometer at gas inlet; verifies valve and meter sizing.
Typical repair: $175–$425 · Water Heater Replacement cost guide
2. Dirty flame rod or igniter failure
How a tech confirms: Inspects and cleans rod; tests igniter resistance.
Typical repair: $185–$395 · Water Heater Replacement cost guide
3. Blocked exhaust or insufficient combustion air
How a tech confirms: Combustion analysis; inspects intake/exhaust per Rheem clearances.
Typical repair: $200–$550 · Water Heater Replacement cost guide
4. Failed gas valve or control board
How a tech confirms: Sequences valve; replaces per Rheem service chart.
Typical repair: $450–$950 · Tankless Water Heater Conversion cost guide

Is this the end of this unit?

Board and valve repairs over $800 on tankless units past 10 years — compare to new tankless with warranty.

How to clear the code

Power button off 10 seconds, on once. Ensure gas and vent clear before retry.

Why clearing is not fixing it: Code 1 clears only after successful ignition — underlying gas or ignition faults repeat.

Which trade to call

Call a licensed plumber who works on water heater equipment. Gas, refrigerant, and combustion faults are not general handyman jobs.

How to find a good plumber

Before you sign a contract for this job, use our guide on how to find a good plumber: verify the licence at the state board, compare three itemized quotes on the same scope, and put permit responsibility and change-order rules in writing.

Read the plumber hire guide Check if your quote is fair Verify licences by state

More codes from this brand

Symptom guide: No Hot Water

FAQ

Rheem tankless code 1 meaning?

Ignition failure — burner did not light and prove flame in time.

Can I fix Rheem code 1 myself?

Gas valve and vent checks only if you are comfortable; most homeowners call a plumber.

Code 1 repair cost?

Often $175–$550 for gas or vent issues; $450–$950 for valve or board.

Does descaling fix code 1?

Rarely directly — but scale can affect heat exchanger performance; mention maintenance history to your tech.

Code 1 vs Rinnai code 11?

Both are ignition-class faults — use the manual for your brand.

Source

Source — Rheem Tankless Water Heater Use & Care Manual — Error Code Table (AP13155). Checked 2026-03-01.