Performed heating maintenance on 8 year old Carrier unit. Cleaned return grates. Checked filters and found them to be in good condition. Temperature rise is within limits. Adjust gas pressure from 3.9â€WC to 3.5â€WC. Measured external static pressure and found it to be a bit high at .9â€WC, mfg recommends .8â€. Inspected blower compartment and found blower wheel to be clean and balanced. Found flame sensor to be heavily sooted up with carbon, I made sure to get this clean. Secondary motor control is within limits. Checked all electrical connections. Tested safety switches. Checked pressure switch. Prior to departure the system is operational after my maintenance inspection.