I am troubleshooting my burner switch also, I have the exact same pressure switch that you do, a PR-16. It was used with my VRT3 trapped pressure unloader and would sometimes get stuck in the on position as of a week or so, a quick reopening of the lance trigger letting hot water to the thermostat is what i believe it takes to turn off the burner as I can turn the dial down and it will shut it self off also.
I have not torn it apart to inspect the spring as mentioned above but the other variable in my system is that I just switched to a ZK7.3 and new higher gpm pump (cannot remember if it has a stock 7.3bypass orifice inside or it was already downstepped to 7.2 from the dealer). , I have solved the pulsation by down stepping the bypass port down to 1/4" return hose to the tank this increased my head pressure to about 400 psi when off the trigger and my pressure cycling issue went away instantly.
Is it okay to have anywhere from 300-400 psi on the gauge to not pulsate/pressure cycle with a k7?
Troubleshooting further my burner will want to stay on when I let go of the trigger *it happened a time or two when still using my old VRT310 unloader. My current PR-16 is mounted on the pump outlet via a T which feeds the input of my k7.
Is this still the correct switch to use if I switched to a k7 and the correct place it needs to be, meaning would a new properly functioning PR-16 stop my burner when the trigger is released and bypass is activated with about 400psi.
Sorry if that is terribly written...