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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 29 Error Fix: Reversed Polarity / Neutral-Ground Cross

The unit has detected reversed electrical polarity or a neutral-to-ground cross in the power supply wiring. The unit requires a properly wired electrical outlet with correct hot, neutral, and ground connections. Use a circuit tester to verify correct outlet wiring. Have a licensed electrician correct any wiring issues. Do not use a 2-prong adapter or ungrounded outlet. This code must be resolved before the unit will operate.

High severity2 fixes available✨ Free fix available

Quick Answer

Error 29 on the A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater means: Reversed Polarity / Neutral-Ground Cross. The top-ranked community fix is “Correct Electrical Wiring with Licensed Electrician” (hard difficulty, ~60 min, DIY cost: $0). 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-$350.

Other A.O. Smith Models with Error 29

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

Combustion Abnormality

2 fixes

Overheat Protection Activated

2 fixes

Over-Temperature Warning

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 29

What does error code 29 mean on a A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater?

Error code 29 on the A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater means: Reversed Polarity / Neutral-Ground Cross. The unit has detected reversed electrical polarity or a neutral-to-ground cross in the power supply wiring. The unit requires a properly wired electrical outlet with correct hot, neutral, and ground connections. Use a circuit tester to verify correct outlet wiring. Have a licensed electrician correct any wiring issues. Do not use a 2-prong adapter or ungrounded outlet. This code must be resolved before the unit will operate.

How do I fix error code 29 on my A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater?

The most successful fix is "Correct Electrical Wiring with Licensed Electrician" (hard difficulty, ~60 minutes). This fix costs nothing. HomeMD has 2 community-ranked fixes for this error.

Is error code 29 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 29 myself?

Yes — the top-ranked community fix ("Correct Electrical Wiring with Licensed Electrician") is rated hard difficulty and takes about 60 minutes. Tools needed: Professional electrician tools.

How much does it cost to repair A.O. Smith GT15-340-NI Commercial 340,000 BTU Commercial Natural Gas Water Heater error 29?

DIY cost: $0. Professional repair typically costs $200-$350. 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), 13 (Combustion Abnormality), 14 (Overheat Protection Activated), 16 (Over-Temperature Warning), and 3 more.

Which other A.O. Smith models have the 29 error?

Error code 29 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)
13 — Combustion Abnormality (2 fixes)
14 — Overheat Protection Activated (2 fixes)
16 — Over-Temperature Warning (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 29 error?

Error code 29 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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