Commercial HVAC repair. Removed and clean burner ignition assembly and intake filters. The heater is now working. Removed and cleaned the filter, sensor, and ignition assembly. Removed and clean sight glass. Adjusted the gas pressure regulator on another unit. The tube heating system has 3 burners and 1 exhaust fan that runs the system. The heating system is 20 years old, but new burners are available. I will work up an estimate. All 3 burners are working at this time.