Depending on the Air Purifier model you have, you might see one or more of the following indicators or codes: * Code: A Auto mode * Code: C Gas mode (AC3254 and AC3256 only) * Code: L Child lock on * Code: UL Child lock off * Code: F0 Clean the pre-filter * Code: A0 to A9 Replace NanoProtect S3 HEPA filter * Code C0 to C9: Replace NanoProtect S3 AC filter * Code SL Sleep Mode * Code 1 h: Timer mode * Code t: Turbo Mode. * Error Code: Er The hall sensor is not working properly. Remove and then reattach the front panel If the error code "Er" still persists, we recommend that you contact us. * Error code: E1 to E4 The appliance has malfunctioned. In this case, we recommend that you contact us.