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A.O. Smith · GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater

A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater 13 Error Fix: Combustion Abnormality

Abnormal combustion has been detected. The unit is sensing an improper air-to-fuel ratio or incomplete combustion. This is often caused by a blocked or undersized vent, inadequate combustion air supply, or a dirty burner. Inspect the exhaust vent for blockages (bird nests, debris, ice). Verify vent lengths and number of elbows are within specifications. Clean the burner assembly. Ensure the installation area has adequate fresh air supply.

High severity2 fixes available✨ Free fix available

Quick Answer

Error 13 on the A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater means: Combustion Abnormality. The top-ranked community fix is “Clean Burner Assembly and Verify Combustion Air Supply” (medium difficulty, ~60 min, DIY cost: $10-$15). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · water heater

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many water heater repairs can be done safely at home, consider hiring a qualified technician if:

This is a high severity error — continued use may cause damage or a safety hazard
The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $200-$300.

Other A.O. Smith Models with Error 13

ATI-540H-N 0.54 GPM 199,900 BTU High Efficiency Tankless Gas Water Heater

water_heater · 2 fixes

Other A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater Error Codes

Ignition Failure

2 fixes

Flame Failure

2 fixes

Overheat Protection Activated

2 fixes

Over-Temperature Warning

2 fixes

Reversed Polarity / Neutral-Ground Cross

2 fixes

Inlet Water Temperature Sensor Failure

2 fixes

Outlet Water Temperature Sensor Failure

2 fixes

Heat Exchanger Temperature Sensor Failure

2 fixes

People Also Ask About A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater Error 13

What does error code 13 mean on a A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater?

Error code 13 on the A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater means: Combustion Abnormality. Abnormal combustion has been detected. The unit is sensing an improper air-to-fuel ratio or incomplete combustion. This is often caused by a blocked or undersized vent, inadequate combustion air supply, or a dirty burner. Inspect the exhaust vent for blockages (bird nests, debris, ice). Verify vent lengths and number of elbows are within specifications. Clean the burner assembly. Ensure the installation area has adequate fresh air supply.

How do I fix error code 13 on my A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater?

The most successful fix is "Clean Burner Assembly and Verify Combustion Air Supply" (medium difficulty, ~60 minutes). Estimated DIY cost: $10-$15. HomeMD has 2 community-ranked fixes for this error.

Is error code 13 on a A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater serious?

This error is rated high severity. You should address it promptly — continued use could cause damage or safety concerns.

Can I fix A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater error 13 myself?

Yes — the top-ranked community fix ("Clean Burner Assembly and Verify Combustion Air Supply") is rated medium difficulty and takes about 60 minutes. Tools needed: T20 Torx screwdriver, Soft brush, Vacuum cleaner.

How much does it cost to repair A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater error 13?

DIY cost: $10-$15. Professional repair typically costs $200-$300. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater have?

The A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater has 8 other known error codes, including: 11 (Ignition Failure), 12 (Flame Failure), 14 (Overheat Protection Activated), 16 (Over-Temperature Warning), 29 (Reversed Polarity / Neutral-Ground Cross), and 3 more.

Which other A.O. Smith models have the 13 error?

Error code 13 also appears on 1 other A.O. Smith model: ATI-540H-N 0.54 GPM 199,900 BTU High Efficiency Tankless Gas Water Heater. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater have?

The A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater has 8 other known error codes:

11 — Ignition Failure (2 fixes)
12 — Flame Failure (2 fixes)
14 — Overheat Protection Activated (2 fixes)
16 — Over-Temperature Warning (2 fixes)
29 — Reversed Polarity / Neutral-Ground Cross (2 fixes)
31 — Inlet Water Temperature Sensor Failure (2 fixes)
32 — Outlet Water Temperature Sensor Failure (2 fixes)
33 — Heat Exchanger Temperature Sensor Failure (2 fixes)

Which other A.O. Smith models have the 13 error?

Error code 13 also appears on 1 other A.O. Smith model:

ATI-540H-N 0.54 GPM 199,900 BTU High Efficiency Tankless Gas Water Heater (water heater) · 2 fixes

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