As a technician at firealarm.com, I recommend checking a few things to troubleshoot your Air Products & Controls SL-2000-P unit. Firstly, ensure that the power supply to the unit is stable and sufficient. Then, check for any loose connections or damaged wiring, as these can often be the culprit behind malfunctions. Additionally, review the user manual for any specific error codes or troubleshooting steps provided by the manufacturer. If the issue persists, it might be necessary to contact technical support for further assistance or consider professional servicing.