Equipment error code

Rheem code 5

Code 5 — exhaust blockage. The unit detected inadequate exhaust flow or excessive backpressure in the vent system.

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

What this code means

Code 5 — exhaust blockage. The unit detected inadequate exhaust flow or excessive backpressure in the vent system.

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

Which models show it

Rheem condensing tankless RTGH and RTG series with sealed combustion venting.

What is actually happening

Unit locks out; no hot water. May follow heavy wind, nest in vent, or condensate backup.

Is it safe to keep running?

Do not operate with suspected blocked exhaust — carbon monoxide risk.

Shut it down when

CO alarm, exhaust smell indoors, or visible blockage you cannot clear safely.

What a homeowner can safely check

Inspect outdoor vent terminal for nests, ice, or lint.
Check condensate drain line on condensing models — full trap blocks exhaust.
Confirm intake and exhaust are not too close together per install manual spacing.

When to stop

Roof vent you cannot access safely.
Code 5 returns after clearing visible debris.

Likely causes ranked

1. Blocked vent terminal or improper termination
How a tech confirms: Draft measurement; inspects per Rheem vent tables.
Typical repair: $190–$500 · Water Heater Replacement cost guide
2. Condensate blockage in neutralizer or drain
How a tech confirms: Flushes condensate path; replaces neutralizer media if clogged.
Typical repair: $165–$385 · Water Heater Replacement cost guide
3. Failed exhaust sensor or pressure switch
How a tech confirms: Tests sensor readings during run; replaces if out of spec.
Typical repair: $220–$475 · Water Heater Replacement cost guide
4. Incorrect vent material or length from install
How a tech confirms: Audits install against manual; re-pipes vent.
Typical repair: $400–$1,200 · Tankless Water Heater Conversion cost guide

Is this the end of this unit?

Major vent rework on older tankless may exceed new unit install — get written vent audit.

How to clear the code

Clear blockage and condensate, power cycle once, run hot tap to call for heat.

Why clearing is not fixing it: Code 5 returns until exhaust flow meets Rheem specs.

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 code 5 meaning?

Exhaust blockage or inadequate vent flow detected.

Can snow block cause code 5?

Yes — keep intake and exhaust clear per manual clearances.

Is code 5 dangerous?

Treat as a combustion safety fault — shut off and ventilate if you smell exhaust.

Typical code 5 repair?

$165–$1,200 depending on condensate, sensor, or vent rework.

Code 5 after power outage?

Condensate in vent or fan delay issues — still needs service if persistent.

Source

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