Start by checking the batteries, if applicable. Then, verify the HVAC system has power and equipment panels are in place. After that it is time for a professional. Adventurous folk may choose to place their trust in YouTube strangers; that's cool and it works sometimes. Changing a thermostat is a manageable task for most handypersons if safety protocols are followed, such as turning off the power first.
A thermostat (stat) is a like a light switch, only it turns heating and cooling equipment off/on instead of a light. In most cases, turning a stat up higher won’t make heat come out any faster or hotter. When the stat wants heat or air conditioning it will display something similar to “heat on” or “system on.” At this point the furnace or AC should be operating. If not, we may verify that the stat is operating properly by isolating it from the control wires.
We turn off power to the system, disconnect the stat wires, install a jumper between individual wires, and then reapply power to test most stats. Generally, the functions of the terminals are as follows:
R = 24 volts
W = heat
G = fan
Y = cooling
C = common (24 volts)
Additionally, to name a few, there maybe be:
W1 and/or W2 = 1st/2nd stage heat
Y1 and/or Y2 = 1st/2nd cooling
When we connect:
R - W terminal/wires we expect the heating system to run.
R - G terminal/wires we expect the fan to run.
R - Y terminal/wires we expect the outdoor AC to run.
If jumping the terminals/wires causes the equipment to function as expected the stat is likely bad. Conversely, if the equipment does not function as expected the stat is likely good and the problem is elsewhere.
We are cautious because all modern stats require electricity. Electricity is dangerous. Even small amounts can destroy equipment components and pose a threat to life.
There are many types of stats; a hierarchy might look like this:
Mechanical - This includes the old round ones. Some old stats contain mercury so please don’t toss them in the trash. We'll gladly submit them to a recycler for you.
Digital - The most popular stat. Illuminated displays, most have batteries, and they can be programmable or non-programmable.
Wireless - Used when running wires from the stat location to the equipment is too difficult.
Wi-Fi - Smart phone users rejoice! Super simple apps make checking in on your home a breeze.
Wi-Fi + Motion detecting or geofencing - Automatic adjustments to save energy when no one is home.
Wi-Fi + Communicating - Installed with a new furnace and AC so the stat and equipment can all talk about the weather and what to do about it.