90
Richmond
Combustion Abnormality / Gas Valve or Fan Control Error
Richmond tankless heater shows error 90 and shuts down; may be associated with poor combustion.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Incorrect gas type or pressure, Blocked burner or vent, Faulty gas valve, Faulty combustion fan control
How to Fix / Troubleshooting
Safety first: Turn OFF power and gas. Combustion issues can be dangerous—use a CO detector in the area.
- Verify gas type: Confirm that the heater is configured for the correct gas (natural gas or LP) and that the supply matches the rating plate.
- Inspect burner and vent: Clean the burner assembly and check intake/exhaust venting for obstructions or improper installation.
- Check air filter (if equipped): Some models have an intake air filter. Remove and clean it if dirty.
- Professional combustion test: A licensed technician should perform a combustion analysis, verify gas pressure, and adjust or replace the gas valve or fan as needed.
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Repair Difficulty
Professional Required
5/5
Required Part
Gas Control Valve
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