How to wire water heater thermostat

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Ordinary water heater

Both elements are never 'on' at same time unless tank is wired for other purpose (see owners manual). This is called 'non-simultaneous operation' since both elements are not 'on' at same time.

Either upper element is 'on' or lower element is 'on,' or both are off.

Upper thermostat is main controller <> it turns on upper element until top 2/3 of tank reaches temperature, and then sends power to lower thermostat. Lower thermostat heats bottom 1/3 of tank, and turns on and off to maintain tank temperature during standby hours when no hot water is being used.

used on 240V water heaters that have 2 elements

Dual element upper thermostat
Screw numbers include L1, L3, L4, T2, and T4
Screw numbers can also be 1, 3, 2, and 4

Single element thermostat
Screw numbers are 1 thru 4
See Larger

120 Volt single thermostat

Ordinary water heater thermostats

Ordinary tank wiring

Ordinary Dual-element 240 Volt residential water heater Look at label on side of tank to find voltage of appliance			Dual-element upper thermostat Larger image
	See larger	Ordinary water heater Both elements are never 'on' at same time unless tank is wired for other purpose (see owners manual). This is called 'non-simultaneous operation' since both elements are not 'on' at same time. Either upper element is 'on' or lower element is 'on,' or both are off. Upper thermostat is main controller <> it turns on upper element until top 2/3 of tank reaches temperature, and then sends power to lower thermostat. Lower thermostat heats bottom 1/3 of tank, and turns on and off to maintain tank temperature during standby hours when no hot water is being used. c
Thermostat reads temperature through wall of tank. If thermostat is not sitting flat against tank, or if factory-provided insulation is missing, or if exterior cover is missing, then thermostat receives cooler air from outside the tank and thermostat mis-reads tank temperature > in this condition, water in tank will overheat. The ECO energy-cut-off or red reset will trip when temperatures exceed 150-180°F. When ECO is tripped, the L1 and L3 screws on upper thermostat have power, but all power below the ECO is turned off.

Dual-element upper thermostat used on 240V water heaters that have 2 elements	Single element 120 Volt or 240 Volt residential water heater Some water heaters have 1 heating element >> Same thermostat used for both 120V or 240V > For correct voltage of water heater, look at label on side of tank
Dual element upper thermostat Screw numbers include L1, L3, L4, T2, and T4 Screw numbers can also be 1, 3, 2, and 4 See Larger	Single element thermostat Screw numbers are 1 thru 4 See Larger	240 Volt single thermostat See Larger 240 Volt single	120 Volt single thermostat See Larger 120 Volt single
		Dual element thermostats See larger

Off -peak water heater thermostats
	Purpose of off-peak ... save energy during peak electric prices. > Upper thermostat operates normally to keep top 2/3 tank hot. > Lower thermostat heats bottom 1/3 of tank when ordered by off-peak meter or timer Compare: Off-peak water heater thermostats Ordinary water heater thermostats 1. Lower thermostat replaced with ECO-protected thermostat identical to upper thermostat. ECO safety red reset cuts off power when water in tank reaches dangerously high 150-180°F 2. Upper thermostat: Red wire is moved L4 to T4. Color of wires can be different. 3. Black wire from lower thermostat does not connect to upper thermostat T4 screw 4. Black wire from lower thermostat runs to top of water heater for connection to off-peak meter, or off-peak timer 5. 240 Volt potential exists between yellow wire and each black wire at top of water heater See Off-peak operation sequence	Ordinary tank wiring
Homeowners should check with plumber before altering water heater wiring.

Ordinary Dual-element 240 Volt residential water heater

Single element 120 Volt or 240 Volt residential water heater

Off -peak water heater thermostats