Gas Burner Adjustment

Midbrook does not recommend setting or adjusting the gas burner unless the operator has been trained by a certified gas burner service technician.


That said, gas burners are set up by measuring the amount of oxygen that is left at the end of the tube by inserting a meter at the exhaust stack.


At the pilot setting that oxygen ratio mix should read 12% - 16%. For the burner to fire consistently, there should not be more oxygen used than that percentage.



  1. In order to regulate the gas air mixture the operator should find the small pilot line’s shut off/adjusting valve.
  2. Open this line for more gas and close for less gas.
  3. Turn the main gas valve off and the unit will stay on the pilot setting during this final adjustment.
  4. Start and stop the unit at least 5 times to make sure the system fires correctly.

The proportionating valve and main gas regulator control low fire.



  1. By turning the top-adjusting stem out or up, it will reduce the output.
  2. The setting should be at 16% oxygen on low fire.
  3. Once the fluid has reached temperature the gas trane should cycle down to this low fire setting.
  4. If the trane goes to low fire and temperature of the water continues to climb, then you should check the pilot setting again or the proportionating valve setting.

High fire



  • When unit is on high fire the oxygen reading should be 4%
  • Control is by the main regulator and the dung valve
  • If the reading is too low, then close down the dung valve until the 4% ratio is reached
  • Normally there is no need to adjust for air flow.