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TROUBLESHOOTING
To function correctly and read temperature accurately, the thermostat must have constant 24-volt pow-
er. If the thermostat temperature is steadily dropping, reading low, or reads 08° when a remote sensor is
installed, it can be traced to one of the three following conditions.
Condition
1. Loss of 24-volt
power.
2. A broken wire on
+, S or - from the
thermostat to the
remote.
3. A shorted or
damaged remote
sensor.
Note: Digital thermostats and remote sensors acclimate very slowly to temperature change. It may take
an hour or more for the temperature to acclimate to the room temperature from a low temperature
reading as outlined above. To expedite the room temperature display use the reset instructions listed in
the installation instructions for the thermostat model you are working with. When reset, the thermostat
will default to a room temperature of 70° and begin sensing room temperature. Be sure to reconfigure
the installer menu for a remote sensor because the reset function may cancel remote sensing.
Pub No. 18-HD86D1-1
Part No. 37-7772002
August 2018
Test
On models with batteries, remove
the batteries and re-install
thermostat. If the display is blank,
check heating and cooling system
to determine why 24-volt power is
absent.
Disconnect sensor wires at
thermostat. Attach a short piece
(2') of three-wire shielded cable to
+, S, and - on the subbase. Bring the
remote sensor to the thermostat
location and attach +, S, and -,
respectively. Reattach thermostat.
If the temperature begins to climb
(slowly), it is reading correctly. If it
reads correctly with the 2' length
but improperly when attached to
the wire run, it indicates a fault in
the wire run.
Because it is an electronic sensor,
there are no Ohm values to test. If
correct conditions as listed in 1 & 2
above and the temperature stays at
or near 08°, it indicates a shorted or
damaged remote sensor.
Comments
For the sensor to read correctly, the
24-volt system power must be present.
Some systems may require an isolation
relay to provide constant power to the
thermostat. Limit or safety devices in
the equipment can also cause a power
interruption.
Repair or replace the 3 wire shielded
cable. Be sure the remote wire run is
not parallel to line voltage wires that
carry heavy inductive loads, or across
fluorescent light ballasts that may
cause an inductance to be transmitted
to the thermostat.
Replace remote sensor.
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