How to Bypass a 4-Wire Thermostat

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Things You'll Need

  • No-contact voltage tester

  • Screwdriver

  • Wire cutter

  • Wire stripper

  • Lineman's pliers

  • Wire nuts

  • Wiring box cover plate

Bypassing four-wire thermostats allows installation in a new location.

The four-wire thermostats used to control baseboard heaters can be bypassed to install a thermostat in another location. On occasion, the wall thermostat does not function well because of its location in relation to windows, doors or the heater itself. Never install a baseboard heater without a means of controlling it. Only perform this repair if a new thermostat will be installed in another location or to test the thermostat and heater.


Step 1

Turn the circuit breaker that supplies the baseboard heater and thermostat to the "Off" position. Remove the thermostat from the wall by removing the screws and test the all the wires with the no-contact voltage tester. The tester should not beep or flash a light as the probe nears the wire if the power is off.


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Step 2

Remove the wire nut connecting a wire on the thermostat marked "Line" or "L1" to a house wire. Separate the two wires. Remove a wire nut from a wire marked "Load" or "T1" and separate the wires. If the house wire ends are badly twisted, cut the wire ends off and strip 3/4 inches of insulation from each wire end. Twist the wires together with the lineman's pliers and twist on a wire nut. Repeat this for the other two wires -- "L2" and "T2" -- attached to the thermostat.


Step 3

Remove the ground wire from the thermostat, if any are attached. Twist the ground wires together with the lineman's pliers and cap them using a wire nut.

Step 4

Fold the wires neatly into the electrical box. Place a blank cover plate over the electrical box and fasten it in place with the supplied screw.


The thermostat will have two wires marked "Line" or "L1" and "L2" and two wires marked "Load" or "T1" and "T2". The object is to connect one "Line" wire -- the wires coming from the circuit breaker -- to one "Load" wire -- the wires leading to the baseboard heater. This completes the connection from the circuit breaker to the baseboard heater.


Never work with the power on, always turn the breaker off while working on your home's electrical wiring.

Do not turn the circuit breaker on and leave it on until a new thermostat has been installed between the breaker the baseboard heater wiring or in the baseboard heater itself. Only turn the breaker on temporarily to test the wiring.


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