How to fix a thermometer on the fritz

The difference between digital and mercury-measures

By Observer Staff
| 6:52 a.m. February 5, 2015

Winter Park - Maitland Observer
Neighborhood

Q: I replaced my home's old mercury thermostat with a digital thermostat about seven years ago. Lately though, the heating seems off: I'll adjust the temperature up a degree or two because it feels too cold, and in a few minutes the house is very hot. All the time, the thermostat shows the room temperature as being exactly what I set it at. Can I recalibrate a digital thermostat, the way that the older mercury thermostats can be calibrated? – Karl J., Buffalo, New York

A: Since digital thermostats don't measure temperature using mercury bulbs — the way older thermostats do — calibrating them doesn't work the same way. They have a temperature sensor that can detect the precise temperature of a room, enabling more exact control of the home's temperature and, ideally, cost savings.

However, you can check to see if the thermostat is measuring the room temperature accurately. This is as simple as taping a mercury or digital thermometer next to the thermostat, so that you get a reading of the air temperature around the device from a second source.

If the thermostat can be calibrated, you'll be able to find instructions to do so either inside the front cover of the device, or in the manufacturer's instructions. (If you lost the instructions, you usually can download them from the manufacturer's website.) Calibration differs between models, but generally brings the temperature set point in line with the sensor.

Several other issues could be causing the apparent touchiness of the thermostat. The sensor could be bad, or there may be a problem with the thermostat's wiring. The device itself may need to be replaced.

Further, your home's heating issue could be unrelated to the thermostat. If calibration doesn't help, have a heating and A/C professional come in a do a system checkup, look for possible problems, and suggest solutions.

HOME TIP: Have you changed your heating system's air filter yet? Do this monthly during the winter to improve efficiency and air quality.