Honeywell RTH2300B manual

Temperature & Hold

Change it until the next period, or keep it on Hold

First set the System switch to Heat or Cool, depending on what you want to control. The large number normally shows the room temperature. Press an arrow once to view the set temperature.

Run resumes the schedule. It does not erase your programmed times and temperatures.

5-2 day programming

Set weekdays together, then the weekend

The RTH2300B has one set of times and temperatures for Monday to Friday and another for Saturday and Sunday. Each uses Wake, Leave, Return and Sleep. It does not offer a separate schedule for every day.

1. Choose Heat or Cool with the System switch. You are programming that mode’s temperatures.
2. Press Set until the screen shows Set Schedule.
3. Use the arrows to choose the weekday Wake time, then press Set.
4. Choose the Wake temperature with the arrows, then press Set.
5. Work through the time and temperature for Leave, Return and Sleep in the same way.
6. Continue with Set to the Saturday/Sunday periods and enter those times and temperatures.
7. Press Run to save and leave programming. To program the other mode, change the System switch and repeat.

If your new schedule seems to be ignored, check whether Hold is showing. Press Run to resume scheduled control, and check that the clock and day are correct.

Clock & day

Set the time before relying on the schedule

1. Press Set. Use the arrows to adjust the time, checking AM or PM when shown.
2. Press Set again and use the arrows to choose the day.
3. Press Run to save and exit.

A flashing clock is not a normal schedule display. Until the clock and day are set, the documented behavior is to use the Monday Wake setting.

Battery replacement

Use two fresh AAA alkaline batteries

Replace them when Lo Batt flashes. The manual also advises replacement each year or before an absence longer than a month.

1. Move the System switch to Off before removing the batteries. The manual warns that equipment could otherwise stay activated.
2. Pull gently at the bottom of the thermostat to release it from the wallplate. Leave the wired wallplate attached.
3. Turn the thermostat over. Replace both batteries, following the marked + and − directions.
4. Reattach the thermostat, set the clock and day, and restore the intended Heat or Cool mode.

The program settings are retained in permanent memory; the clock and day need setting again. If the housing does not release normally or your battery compartment differs, stop and check the instructions for the model on your label.

Display messages

Flashing Cool On can be the restart delay

The documented compressor protection waits about five minutes before a restart. During that wait, Cool On flashes; on a heat-pump installation the message can be Heat On.

Allow the delay to finish. If the system still does not respond, check the System switch and that the set temperature requests heating or cooling. Persistent failure needs the model’s troubleshooting instructions or service, rather than repeated resets or disabling compressor protection.

The manufacturer warns against running cooling when it is below 50°F (10°C) outdoors. Do not use cooling as a test in those conditions.

Model check

A similar faceplate is not enough

Check the full model on your paperwork or the back of the thermostat. For these models, put the System switch in Off before releasing the thermostat from its wallplate. Keep the wallplate and wiring in place.

These instructions apply to RTH2300B1012 and RTH2300B1038. The official support page groups both models. The RTH221 shares a manual but uses a different schedule arrangement; the similarly named RTH230B is a different model.

This page covers everyday operation, not wiring, installer configuration or equipment diagnosis. Use the exact installation instructions and qualified help for those tasks.