Honeywell T8501, Product Data, Page: 14 / 16

T8501 AND T8511 DELUXE ELECTRONIC THERMOSTATS
68-0162—1 14
Symptom Possible Cause Action
Heating will not come on. No power to the
thermostat. • 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 at the equipment is in the Off
position—set to 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.
Thermostat minimum off
time is activated. Wait up to five minutes for the system to respond.
System selection is not
set to Heat. Set system selection to Heat.
O/B terminal configured
incorrectly
(select
models).
Check Installer Setup number 29 and reconfigure correctly.
O or B terminal
miswired (select
models). Check system description to determine whether changeover should be
energized in heat (B) or cool (O). Rewire if necessary.
Cooling will not come on. No power to the
thermostat. • Check that C terminal is connected to the system transformer.
• Check for 24 Vac between C and R or RC and Y 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 at the 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.
Thermostat minimum off
time is activated. • Wait up to five minutes for the system to respond.
• Enter Installer Setup mode number 33. Reconfigure minimum off
time (if required).
System selection is not
set to Cool. Set system selection to Cool.
O/B terminal configured
incorrectly
(select
models).
Check Installer Setup number 29 and reconfigure correctly.
O or B terminal
miswired (select
models). Check system description to determine whether changeover should be
energized in heat (B) or cool (O). Rewire if necessary.
System On indicator is lit,
but no heat is being
delivered. Heating equipment is
not operating. Verify operation of heating equipment in system test.
Outdoor temperature
not displayed
(select
models)
Option not activated. Enter Installer Setup number 24 and set to 01. Thermostat must have
OT terminals and a C7089B1000 installed.
Outdoor temperature
display is incorrect (select
Outdoor sensor is
connected incorrectly. Refer to C7089B1000 installation instructions and check wiring
between the thermostat and sensor.
models)
Wrong sensor. Replace sensor with C7089B1000 sensor.
TROUBLESHOOTING GUIDE (continued)