Reset the burner controller, located on the front of the gas burner, by pressing the controller's manual reset button.
Locate the high pressure/temperature switch, located near the burner controller, and press the manual reset button on the switch to reset the device.
Locate the gas pressure switches on the boiler's fuel train, and press the manual reset button on both of the switches.
Locate your water monitor. If the monitor has a reset switch, activate this switch as well. In some cases, resetting this device will indicate that there isn't enough water in the boiler.