Honeywell RTHL3550D Troubleshooting

You can change the temperature adjustment but the HVAC system does not respond to your changes.

If the thermostat is a newer digital model, try replacing the batteries. This usually involves removing the faceplate to access the battery compartment. Remove and replace the faceplate carefully so as not to bend the connection pins.

Slider needs cleaning

Older thermostats that use a slider to set the temperature have moving parts that can become coated with dust and grease over time. Remove the face-plate and clean slider and slider housing.

• With a cotton swab, lightly dipped in rubbing alcohol and clean the area.
• Using short bursts from a compressed air electronics cleaner, blow dust and debris from the thermometer spring and housing interior.

There is no easy remedy. Replace with new unit.

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HVAC system does not react to thermostat changes

Press SYSTEM button to set system to Cool. Make sure the temperature is set lower than the Inside temperature.

• Check circuit breaker and reset if necessary.
• Make sure power switch at heating & cooling system is on.

The coil springs may be broken or damaged. There is no easy remedy to fix this with the unit and it still accurately display the temperature reading. Replace whole thermostat with a new unit.

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Your Honeywell RTHL3550D fails to turn off HVAC system once set temperature is achieved

The coil springs may be broken or damaged. There is no easy remedy to fix this with the unit and it still accurately display the temperature reading. Replace whole thermostat with a new unit.

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Any of the circuit board components may be broken or defective. Inspect these carefully.

May also be due to corrosion. If corrosion is found, clean thoroughly with rubbing alcohol and cotton swap.

If cleaning techniques don't work, some of the circuit board components may be broken or defective. Unfortunately, replacement parts are not easily available, so thermostat must be replaced.

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Casing is damaged; buttons, knobs, sliders are non-functional

There is no easy remedy. A face-plate or mounting plate from an old identical thermostat may be used. However, these parts are not sold separately and may be hard to obtain. Replace with new unit.

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