EM Heat (Emergency Heat) is a setting on heat pump thermostats that manually activates the secondary or backup heating system—typically electric resistance heating—when the primary heat pump is malfunctioning, defrosting, or unable to maintain comfortable indoor temperatures. It is designed for temporary use to prevent damage to the heat pump or provide supplemental heat in extreme cold.
The term “Fan” on an air‑conditioning unit refers to the component that moves air through the system. Understanding fan settings helps users control airflow, temperature, and energy use in both home and vehicle AC systems.
“Em. Heat” is an abbreviation for emergency heat, a supplemental heating mode used by heat‑pump systems when outdoor conditions prevent normal operation. The indicator appears on thermostats and control panels to signal that auxiliary heating is active.
The ‘Hold’ function on a thermostat is a setting that overrides a pre-programmed schedule to maintain a single, constant temperature. It allows users to manually lock in a specific heat or cool setting regardless of the time of day.
Hold temp on a thermostat refers to a feature that maintains the current temperature setting continuously, overriding programmed schedules until manually changed or canceled.
A water leak from an air conditioner usually signals normal condensation, a blocked drain line, or a malfunctioning component. Understanding the cause helps prevent damage and maintain efficient cooling.
E1 on an electric heater typically indicates a temperature sensor malfunction, overheating, or a communication error between the control board and sensor. This error code is common in many heater brands and often requires checking the sensor, restarting the unit, or contacting support.
On AC manifold gauges, the term ‘retard’ refers to a dampening feature that slows the needle’s response to pressure changes, allowing technicians to obtain more stable and accurate readings during fluctuating refrigerant conditions.
The “CIRC” indicator on many thermostats refers to the circulation pump that moves hot water through a hydronic heating system. Activating CIRC allows the pump to run without a heating call, helping balance temperatures, prevent pipe freezing, and provide hot water to radiators on demand.
Emergency heat is a backup heating mode on heat‑pump thermostats that activates when the primary heat source cannot meet demand. It uses electric or gas resistance heating, consuming more energy but providing reliable warmth during extreme cold or system faults.