Installing an electric thermostat to replace an old one is a DIY task that can pay good dividends and is relatively simple. Make sure the thermostat you buy is rated to do the job by checking the specifications and comparing them with the demand you will place upon it.
Step 1 – Turn off the mains power supply.
It may be that you have an isolation switch that can cut the power to the equipment controlled by the thermostat without affecting the whole house. If so, open the switch and check that the power is off using a mains tester.
Step 2 – Take face plate off old thermostat
Check with the mains tester each of the cables that are exposed and make a note of which cables are connected to which terminal. If the cables are not color coded you will need to be especially careful when you disconnect them
Step 3 – Disconnect Cables
Disconnect each of the cables from the old thermostat, making careful note of the color and which terminal it was connected to. If the cables are not colored, label each one you detach with the details of which terminal it was connected to. Be careful not to let the cables fall back into the wall.
Step 4 – Remove Old Thermostat
After you have disconnected all the cables, remove the old thermostat from the wall, again making sure the cables do not fall back into the wall.
Step 5 – New Thermostat
Attach the new thermostat to the wall, making sure that all cables are pulled through the thermostat housing. If the existing screw holes are positioned conveniently, you might not need to drill new holes but it might be helpful to use wall plugs to ensure a good tight fix.
Step 6 – Check Cables
Carefully examine the insulation of the cables and, if necessary, cut the ends of the cables and strip about 1/2 inch of insulation from them. This check is very important because exosed insulation can dry and crumble.
Step 7 – Connect Cables
Referring to the notes you made or the labels attached to the cables, connect the cables to the correct terminals in the new thermostat. Refer to the thermostat instructions if you have any questions.
Step 8 – Double Check
All the terminals need to be connected tightly so there is no danger of them slipping out. You should double check to make sure you have connected the cables correctly.
Step 9 – Fix thermostat face plate
Make sure the thermostat face plate is properly located and that it is not twisted or has any retaining screws missing. Often the weight of the cables falling back into the wall is enough to locate and hold the face plate in position while you drive the screws.
Step 10 – Turn on Power
Once everything is ready, turn on the main power and test the thermostat.
Replacing an old thermostat can be a money-saving exercise as the new one will be more accurate and responsive.