With you mentioning the burst disc, I am going to surmise you've got a HydroTek SS skid. It should have a pressure switch mounted on the unloader. Take the 4 small screws out of the cover and remove it. You may have to take the 2 allen head screws out where the black plastic block mounts to the brass actuator and remove it to get to them. If you remove the box from the actuator, look at the pin that comes out the end. It should be flush or real close to it. If it is not, the spring inside the actuator may be broken, not pulling the pin back in on unload. If the pin is ok, pull the top wire (the one mounted by itself at the top of the microswitch, and see if the burner still comes on. If it does, the solenoid on the burner may be stuck in the "on" position. Do not replace it with a Ford style starter solenoid. Go to NAPA or Bumper to Bumper, you know, one of the auto parts stores where they still know auto parts, not just part numbers, and ask for a constant duty solenoid. If the switch or spring is bad, replace them (it).
