thermostat chirps

[author]

My Robert Shaw makes a chirping noise, but only in the middle of the night. The Robert Shaw people say that their products do not make any noises- but, I've stood next to the damn thing at 300 AM and it is chirping, any ideas?

[LazyPup]

As a rule thermostats work on one of two technologies; Electro-Mechanical or Digital Electronics.

The conventional elctro-mechanical type thermostat relies upon a very lightweight Bi-metal spring that is wound in a coil form and expands when heated or contracts when cooled. One end of the spring if permanently affixed to the frame of the thermostat while the opposite end moves between electrical contacts to turn on either the heat or AC unit. There simply is no device inside an electro-mechical thermotat that would even be capable of creating a sound.

In a Digital Thermostat a slight current is passed through a Thermistor (Thermally variable resistor) and the output current feeds into a digital logic circuit that electronically compares the actual temperarture to the preset desired temperature and switches electronic relays accordingly. Here again, there simply is no component capable of producing a sound.

Having said all that, nonetheless we cannot dispute the fact that you are hearing a chirping sound so we must now consider the possibilities.

You stated in your post that the sound is only produced in the night. This is remotely possible, but it is more reasonable to believe the sound may be produced at other times but just goes unnoticed during the day when we have all the other sounds of normal household activity (Radio, TV, appliances, children, street noise etc.) There are many such noises in our homes that we give no conscious thought during the day but at night they are as annoying as a freight train to a light sleeper.

I can think of two possibilities here.

1. Your thermotat may be mounted on a wall in a hallway where there are no other devices readily apparent that would produce a sound so you might be assuming the sound to originate with the thermostat. Is is remotely possible that there is also a smoke detector overhead in the immediate vicinity of the thermotat? Battery powered smoke detectors or hard wired smoke detectors with battery backup have a low battery indicator that chirps.

2. The second possibility, although I have never personally encountered one, you may have a digital programable thermostat with a battery backup and it may also have a chirping signal to indicate a low battery condition.

[author]

It was the smoke detector located way above the thermostat- it has malfunctioned, it did not chirp during the day, when the heat is on, but I took it down, put it outside and it chirped away.
thanks for the suggestion and the info