How to Hook Up a Thermostat to a Circulating Pump

heating system circulating pump
  • 4-8 hours
  • Intermediate
  • 400-900
What You'll Need
Allen wrench
Wire stripper
Wire nuts

If you have installed a circulating pump in your hot water system, you may have also decided that the efficient method to keep it running properly is to also install a thermostat and control. Like any thermostat, the circulating pump thermostat is used to regulate the temperature of the hot water and turn on and off the pump as necessary to ensure that hot water is appropriately flowing through your home without expending unnecessary energy.

Step 1 - Prepare to Install Thermostat

Turn off water to the circulating pump. Drain any excess water out of the system and close isolation valves that are on both sides of the circulator. Make sure that you have appropriate wiring available to hook up the thermostat. You may wish to also turn off the breaker for safety.

Step 2 - Terminal Box Position

Before you install the thermostat the pump motor shaft must be horizontal. Make sure that the terminal box is on the side of the motor housing. Ensure that the terminal box not be located below the motor housing. Changing the terminal box position: remove four Allen screws. Hold the motor housing while removing the Allen screws. Taking care, rotate the motor to the desired position. Replace the Allen screws and tighten to 7ft-lb torque, making sure that the motor shaft turns easily, with no obstruction.

Step 2 - Install the Thermostat

The thermostat needs to be installed directly on the pipes for the system to work properly. Install the thermostat controls. Be aware that clip on thermostats cannot be used with line cord type controls. It is a temperature sensing device and it must be able to pick up the temperature of the water in order to function well. The thermostat can either be clamped on or clipped on depending on the model of the thermostat.

Also keep in mind that there are different types of thermostats depending on whether the pipes are copper or steel. A thermostat will not work efficiently on PVC piping because of the insulation quality of PVC.

Step 3 - Hooking up the Electrical Wiring

There is a yellow or white wire, and a black wire that need to be connected to the wiring in your house to communicate the temperature variances back to the circulating pump. Hook the black wires together using wire nuts and do the same with the white or yellow wires. Several states require a licensed electrician to connect the wiring for a thermostat for compliance to codes in your area.

Step 4 - Finish and Test Installation

Before you turn on the circulation system the pump needs to have water in it, so turn the valve for the pump on to fill the tank with water. Make sure to vent the system as well. Turn on the breaker and the circulator switch. Ensure that the thermostat is working properly by monitoring the system for a few hours and ensure that the circulator is turning on and off appropriately with the setting on the thermostat.