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Tech Tip: Checking Modulating Gas Valve on ComfortBridge™ Furnaces
The ComfortBridge™ Modulating Furnace utilizes a 24VAC electrically stepped gas valve by White Rodgers. During the first heating cycle, the furnace operates at 100% firing rate. Afterward, the internal control algorithms adjust the gas valve and induced draft blower to regulate the gas input as needed.
Key Functions of the Modulating Gas Valve:
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Controls main burner gas flow
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Regulates gas pressure
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Provides 100% safety shut-off
Important Notes:
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Upon power-up, the gas valve stepper motor may activate, producing a slight clicking sound. This is a normal calibration process and does not indicate a malfunction.
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The front cover pressure switch is wired in series with Pin 5 (24V hot) on the gas valve. If the valve is not receiving voltage, ensure the front cover pressure switch is closed.
Recommended Voltage Checks:
| Pin # | Label | Function | Expected Voltage |
|---|---|---|---|
| 5 | TH | Main Valve | 24 VAC |
| 4 | TR | Ground | - |
| 3 | TX | Communication to IFC | 3.3 VDC |
| 2 | RX | Communication to Stepper | 5.0 VDC |
| 1 | TH | Board 24V | 24 VAC |
For proper diagnosis, verify these voltages during troubleshooting. If readings are outside the expected range, further investigation may be required.
