Hello, out Worcester Bosch oil boiler has locked-out and will not re-set with either of the re-set buttons. None of our local plumbers can get here until some time next week. The suggestion is that we try to clean the photo-cell. We can find the photo-cell OK but we cannot get it to come out! It goes straight down into the metal housing, should we just pull harder or is there a special technique to get it to come out?