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How Thermostats WorkThermostats are the “brain” of today’s HVAC systems. The old-school manual units of the past that performed simple “on/off” functions of the A/C or furnace are virtually extinct. Digital programmable thermostats are now the industry standard.

The basic function of a thermostat is to maintain a preset indoor temperature consistently. To do this, the thermostat must accurately sense present room temperature inside the house, then actuate an air conditioner or furnace to adjust that temperature up or down to the desired setting. In old-fashioned manual units, heat-sensitive metal strips tipped a mercury switch to activate heating or cooling. Today’s digital units, however, utilize an electronic component called a thermistor to sense heat, in conjunction with a microprocessor to control the furnace or A/C.

Because it’s actually a small computer, a digital thermostat automates functions that enhance control and convenience. These include adjustable settings for different temperatures at different times of the day, as well as different days of the week. “Hold” and override settings permit you to temporarily depart from programmed settings, while temperature settings for special events like vacation are simplified. Most models can remind you when maintenance like regular filter changes are required and inform you when a system problem is detected.

Today’s digital thermostats have no moving parts and are generally very reliable. However, here are some potential issues and simple thermostat problem-solving:

No display.

Usually this means no power to the thermostat. Check the batteries inside the unit if it is battery powered. If it’s wired to house electricity, check for a tripped circuit breaker.

Thermostat turns on/off at wrong temperature.

A calibration function included in most digital thermostats may restore temperature accuracy. Consult manufacturer’s instructions.

HVAC operation is inconsistent.

Make sure the thermostat isn’t affected by direct sunlight, cold/hot breezes from a nearby exterior door or other external influences that may skew accurate temperature sensing. Relocate unit if necessary.

Furnace or A/C doesn’t respond.

Verify that the thermostat is set to “On” and the correct desired heating or cooling mode.

For more about operation and professional service for today’s digital thermostats, contact Detmer and Sons.

Our goal is to help educate our customers in Dayton, Ohio about energy and home comfort issues (specific to HVAC systems). 

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