Noritz · Water Heater error code

99Combustion / vent blockage lockout

Cross-checked Licensed pro only

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Stop: this involves gas or the sealed refrigerant system.

OnCall Tech only describes the symptom. Gas work needs a licensed gas technician, and refrigerant work requires EPA Section 608 certification. If you smell gas: shut off the supply if it is safe, do not switch anything on or off, ventilate, leave the building and call the gas utility.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

Related diagnostic guides

Guide · Water Heater

Power-vent gas water heater: blower won't start, runs without firing, or locks out

Power-vent tanks add a 120 V blower, an air pressure switch and often a vent temperature limit. Most no-heat calls are electrical supply, a kinked or water-filled pressure switch tube, condensate in the blower, or a restricted vent. The tech checks power and the low-voltage safety chain and inspects visually; gas valve, burner, igniter/flame sensor and vent repairs are referred to a licensed gas technician.

10 steps ~45 minmoderate

Install · Water Heater

Gas water heater replacement (BLOCKED: refer to a licensed plumber / gas installer)

Replacing a gas water heater involves the gas connection, flue venting and combustion air, which are licensed work. The handyman role is to assess, take immediate safety action and refer.

3 steps ~15 minadvanced

Guide · Water Heater

Tankless: error code, no ignition at low flow, or temperature swings

Many tankless complaints are water-side: flow below the activation threshold, a clogged inlet screen, low-flow aerators, or scale in the heat exchanger. Gas supply, venting and combustion codes are blocked: diagnose and refer. Read the code first, then work the water side.

6 steps ~90 minmoderate

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Service due warning

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Combustion / exhaust problem

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Ignition failure

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Flame loss / weak flame

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Thermal fuse tripped (heat exchanger overheat)

Cross-checked High-voltage / caution

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Outlet temperature spike (often scale)

Cross-checked High-voltage / caution