Tip & How-To about Heating & Cooling

Thermostat Line Voltage How to Install or Replace

You either have a new line voltage thermostat or have to replace your old line voltage thermostat. In either case the process is much the same.



  1. Make sure that all power is turned off at the breaker panel. Most heaters that use a line voltage thermostat usually use 240v current so the breaker will either be a double pole breaker or you will need to turn off two single pole breakers to kill all of the power.
  2. Check to see which wires are hooked to the breakers. In most cases it will be the red and black wires, but I have seen many times that the white and black wires were used. Often there is no red available when the white is used.
  3. Take out the two screws that hold the thermostat to the junction box. When you get the thermostat out make a note of which wires go to the heater (load) and which wires are coming from the breakers. (line)
  4. If you have a single pole thermostat installed one of the sets of wires may be wired straight through the box or have the line and load wires connected directly in the box. With a double pole t-stat you will have both sets of wires running through the t-stat.
  5. Remove the old thermostat and wire the new t-stat in the circuit with the load wires hooked to the load or heater and the line wires hooked to the wires coming from the breaker. Make sure to get a very good tight connection as resistance loads will heat up quickly if good contact is not made. This poor connection can and will start fires.
  6. Turn the power on and check the heater for heat output.
  7. Turn the power back off and carefully screw the thermostat to the junction box securely. Then you can reapply the power to the circuit.

Now you are up and running with a new line voltage thermostat installed.

http://www.fixya.com/support/r3894275-manual_honeywell_find_honeywell_manuals

http://www.fixya.com/support/r3623083-thermostat_wiring_terminal_designations

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2 Answers

I am installing a new thermostat for my baseboard electric heat. The electric box has 2 wires comming into it. So I have 2 black, 2 white and 2 ground. The old thermostat had a place for all 4 wires (one side line one side load) the new thermostat is a honeywell RLV430 High voltage (at least I got the high voltage part right). It only has 2 wires so I am at a loss as to what to hook up where. My inclination is to hook the load to one and the line to the other. But I don' know if this is right


One wire is "IN" the other is "OUT" A Thermostat works by "Breaking" the "Phase" line. It is just that simple. You usually have a pair of wires that connects, on the "Hot" side, to the always power ON line, & neutral. The Circuit, or Load, on the "Cold" side, has a a pair of contacts that open & close depending on Thermostat, in series with that conductor. Hot Contacts Cold P In-------------------><-----------------P Out
N----------------------------------------------------N

Mar 04, 2010 | Honeywell Programmable Thermostat Heater

2 Answers

thermostat installation


On paul 306, I don't have any info on you're system, but the old thermostat that has the smaller wires with the colors you described is a low voltage (24volt) controls. The new one you purchased sounds like it is for a system that is made for line voltage (120 volts or more) connecting this to the unit may have bad results. This also may apply to GUEST.
COACOOCHEE, the white and black coming into the box is the line, even though white should not be used for line, the connections for the other side of the thermostat is the load. The new thermostat you have be a single pole break as opposed to the old one may be a double pole. You should have a meter to check the voltage coming into the box, it may be 120 or 220 depending on what you have. Without any more info I cant be sure, but you may be able to connect the black wires to the switch and the white together. But it would be wise to test with a meter to be sure before doing this.

Nov 16, 2007 | Honeywell Programmable Thermostat Heater

1 Answer

Water isn't heating up and not drying


Check with a multi-meter for voltage (220/115v) on heating element's tags. If you can read this voltage on tags - you should replace the heating element In case you can't read voltage on its tags, disconnect one of the wires from its tag (you should unplug first your machine's power cable!) and test for element's resistance - If you can read its resistance, you should replace the thermostat. In case of no resistance - you should replace element and thermostat Good luck!

Mar 12, 2007 | Zanussi 18 in. ZSF4123 Slim-Line...

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