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Articles
NEWS | Aug. 6, 2020

WH-400 Water Heater: Knock Out Lockout

This article initially appeared in PS 761 (Apr '16), p. 45.

The WH-400 water heater works on a simple principle, operators. You turn it on, the fuel valve opens and sprays fuel through the fuel nozzle, and the electrodes energize to create a spark that lights the fuel.
 
At each startup, the primary safety control performs a "trial for ignition" (TFI). If the flame doesn’t start within several seconds, a buzzer sounds and the water heater is locked out. This is called a safety lockout.
 
No problem. Just press the red FLAME RESET button for one second and you’re ready to try again.
 
But if it’s a new WH-400, or you’re trying to start one that’s had its fuel drained for transport or storage, it may take several tries to get the heater started. And if the primary safety control does three safety lockouts in a row, the control enters a restricted lockout.
 
In restricted lockout, pressing the FLAME RESET for one second again does nothing. That leads some operators to assume they have a bad primary safety control, NSN 4540-01-575-2421, so they order a new one.
 
Here’s a little known fact: To release the water heater from a restricted lockout, press and hold the FLAME RESET button for 60 seconds. Now you’re all fired up.

FLAME RESET button location
Press FLAME RESET button one second for safety lock
and 60 seconds for restricted lockout

 
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