We would recommend you try resetting the unit as indicated below. Be sure when you reset that you completely remove power from the indoor display unit by removing batteries and unplugging the unit.
Before proceeding with the reset, please check your batteries. We recommend that the batteries meet the following criteria:
• Verify you are using standard alkaline batteries such as Rayovac or Energizer. Lithium batteries can be used in the outdoor sensor if you are in a location that will frequently see temperatures below -4oF/-20oC. (Rechargeable batteries, as well as batteries that indicate a heavy-duty quality are not recommended, and may cause irregularities.)
• Verify that you are using a fresh set of batteries. The battery expiration date should be at least 6 years out. Batteries can lose 3% of their power or more every year in storage.
1. Bring both the sensor and display unit indoors and position them side by side.
2. Remove all batteries from both the sensor and the display unit. (If the display has an AC adapter, please unplug this, as well, to completely power down the unit.)
3. Locate the A-B-C ID switch inside each battery compartment. Make sure that the two parts are set to the same position. Please change both parts to the next available letter on the ID switch, as this can help to reset the unit.
4. Reinstall batteries in outdoor sensor first.
5. Reinstall batteries (and/or reconnect AC adapter) to the display last.
6. Let both sensor and display sit side by side to establish connection. (Leaving the devices side by side for 30 minutes will allow you to verify accuracy by comparing the indoor and outdoor readings shown on the display. For accuracy standards, please visit http://www.acurite.com/accuracy.)
7. After a connection has been established, the sensor can be placed outdoors.
Please let us know if these steps were successful, or if we can offer any further assistance, as we want to be sure that the issue has been resolved.