Troubleshooting Guide - Honeywell T8501 Installation Instructions Manual

T8501 MICROELECTRONIC THERMOSTATS

TROUBLESHOOTING GUIDE

Symptom Possible Cause
Display will not Thermostat is not being
come on. powered.l
Thermostat microprocessor is
locked up.
Temperature Room temperature display has
display is incorrect. been reconfigured.
Thermostat is configured for °F
or °C display.
Bad thermostat location.
Temperature The upper or lower temperature
settings will not limits were reached.
change. (Example:
Cannot set the
The setpoint temperature range
heating higher or
stops were configured.
the cooling lower.)
Heating will not No power to the thermostat.
come on.
Thermostat minimum off time is
activated.
System selection is not set to
Heat.
69-0925—4
Table 5. Troubleshooting Guide.
• Check that C terminal is connected to the system
transformer.
• Check for 24 Vac between C and R or RH terminals.
— If missing 24 Vac:
— check if the circuit breaker is tripped—reset the circuit
breaker.
— check if the system fuse is blown—replace the fuse.
— check if the power switch on the HVAC equipment is in
the Off position—set to the On position.
— check wiring between thermostat and HVAC
equipment—replace any broken wires and tighten any
loose connections.
— If 24 Vac is present, proceed with troubleshooting.
Remove the thermostat from the wallplate for two minutes. After
two minutes, replace the thermostat on the wallplate.
Enter Installer Setup number 37 and reconfigure the display.
Enter Installer Setup number 14 and reconfigure the display.
Relocate the thermostat.
Check the temperature setpoints:
• Heating limits are 40 to 90°F (4.5 to 32°C)
• Cooling limits are 45 to 99°F (7 to 37°C).
Check Installer Setup numbers 34 and 35 and reconfigure the
setpoint stops.
• Check that C terminal is connected to the system
transformer.
• Check for 24 Vac between C and R or RH terminals.
— If missing 24 Vac:
— check if the circuit breaker is tripped—reset the circuit
breaker.
— check if the system fuse is blown—replace the fuse.
— check if the System switch on the HVAC equipment is
in the Off position—set to the On position.
— check wiring between thermostat and HVAC
equipment—replace any broken wires and tighten any
loose connections.
— If 24 Vac is present, proceed with troubleshooting.
Wait up to five minutes for the system to respond.
Set system selection to Heat.
10
Action