I would use the switch as a base to lever up and off the terminal with a flat bladed screwdriver, it will certainly come off.
Check (with that one wire removed) that both heating elements are on by feeling the hot water temperature, if so, then almost certain to be a (the) faulty neon pressure switch, just renew it.
Check (with that one wire removed) that both heating elements are on by feeling the hot water temperature, if so, then almost certain to be a (the) faulty neon pressure switch, just renew it.
