TH5110D NON-PROGRAMMABLE THERMOSTAT
11 69-1712—1
TROUBLESHOOTING
Table 5. Troubleshooting
Symptom Possible Cause Action
Display is blank. Thermostat is not powered. Check for 24 Vac between Rc and C.
Check that fresh AAA alkaline batteries are
installed as marked on the battery holder.
Temperature settings do
not change.
The highest or lowest temperature
setting was reached.
Temperature setting range:
H e a t i n g : 4 0 ° F t o 9 0 ° F ( 4 . 5 ° C t o 3 2 ° C )
Cooling: 50° F to 99°F (10°C to 37°C)
Heat does not turn on
(Heat On is solid in the
display).
Heating equipment failure. Check for 24 Vac at the equipment on the
secondary side of the transformer between
power and common. If voltage is not
present, check the heating equipment to
find the cause of the problem.
Check for 24 Vac between the heat terminal
(W) and transformer common. If 24 Vac is
present, the thermostat is functional. Check
the heating equipment to find the cause of
the problem.
Loose or broken wire connection
between thermostat and heating
equipment.
Check for 24 Vac between the heat terminal
(W) and transformer common. If voltage is
not present, check wire connection (loose or
broken) between the thermostat and the
heating equipment.
Cooling does not turn on
(Cool On is solid in the
display).
Cooling equipment failure. Check for 24 Vac at the equipment on the
secondary side of the transformer between
power and common. If voltage is not
present, check the cooling equipment to find
the cause of the problem.
Check for 24 Vac between the cool terminal
(Y) and transformer common. If 24 Vac is
present, the thermostat is functional. Check
the cooling equipment to find the cause of
the problem.
Loose or broken wire connection
between thermostat and cooling
equipment.
Check for 24 Vac between the cool terminal
(Y) and transformer common. If voltage is
not present, check the wire connection
(loose or broken) between the thermostat
and the cooling equipment.
Fan does not turn on in a
call for heat (electric
furnace).
Fan Control in Heating (Installer Setup
Number 3) is set to Gas or Oil Furnace
(Setting 0).
Set Fan Control in Heating (Installer Setup
Number 3) to Electric Furnace (Setting 1).
Heat pump puts out cool
air in the heat mode and
warm air in the cool
mode.
Changeover Valve (Installer Setup
Number 2) is not configured to match the
changeover required by the installed
heat pump.
Set Changeover Valve (Installer Setup
Number 2) to match the changeover
required by the installed heat pump.
Both the heating and
cooling equipment are
running at the same
time.
The heating equipment is not a heat
pump but the System Type (Installer
Setup Number 1) is set to Heat Pump
(Setting 1).
Set System Type (Installer Setup Number 1)
to match the installed heating and/or cooling
equipment.
Heating and cooling wires are shorted
together.
Separate the shorted heating and cooling
wires.
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