Why is the pressure in my oil burner 40 psi ?
changed expansion tank no change hot water still blowing from valve onto floor
The reason why your pressure in the oil burner is 40 psi could be because of the boiler getting over pressurized. The best thing to do is to get an oil burner inspection specialist to look at it and fix the problem.
I'm guessing you have a boiler? If that's correct call a professional. Boilers can be quite dangerous if not maintained properly.