You will see it up on the right hand side of the main heat exchanger, wired in series with the overheat stat (it’s the bigger one of the two). Take off the short bit of wire that links the two and keep it safe.. Next take the remaining spade connector OFF the low water pressure switch, and fix it to now-vacant terminal on the overheat stat. Now you’ve linked out the pressure switch totally.
Try n fire the boiler and it will work – promise.
You must NOT leave this switch disconnected, it is there for a safety reason, but sometimes they can be cleaned out.