43
Keeprite
Gas Valve or Modulation Fault
Furnace LED shows code 43; unit may not modulate or stage correctly.
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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
Faulty two-stage or modulating gas valve, Incorrect gas valve wiring, Low or high inlet gas pressure, Control board modulation output failure
How to Fix / Troubleshooting
Safety: Turn off gas and power. Gas valve work must comply with local codes.
Steps:
- Inspect gas valve wiring: Compare wiring to Keeprite diagram. Ensure stage 1 and stage 2 (or modulation) terminals are correctly connected.
- Check gas shutoff: Confirm manual gas valve is fully open and that there are no additional closed valves upstream.
- Do not adjust gas pressure: Inlet and manifold pressures must be measured and adjusted only by a licensed technician with a manometer.
Gas valve and modulation faults directly affect combustion safety and should be diagnosed and corrected by a professional.
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Repair Difficulty
Professional Required
5/5
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