Resetting the filter on a Honeywell RTH230B is easy and can be done in just a few simple steps. First, turn off the power to your air conditioning system. Then locate the filter access door near the return air grille of your unit. Open this access door and remove any existing filters from inside the cabinet. Once all existing filters have been removed, take out your new Honeywell RTH230B filter and insert it into the slot with its arrow pointing up towards you. Finally, close up the access panel and turn on power to your AC system again so that it can begin using its new clean filter! Following these instructions will ensure that your Honeywell RTH230B filter is reset properly for optimal performance of your air conditioning system!