ALM 3 means a high limit safety switch has opened. There are three possibilities and they are very different. A condensate trap pressure switch fault is usually a blocked or undersized drain and is resolved by cleaning. A water supply high limit fault auto resets once the temperature drops 10 degrees Fahrenheit below setpoint and points to a pump, blower or sizing problem. A vent limit switch fault is serious: that switch is not resettable, it must not be bypassed, and Gradient’s manual states the heat exchanger must be replaced.

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