They can be a total pain to actually get at. I once broke the soldered joint on the pipework changing an AAV on a Grant Combi. Luckily I was able to solder it up. I know use a spanner on the brass bush that the AAV screws into and one of these:-...
Are you sure the boiler didn't run briefly but overheat due to lack of circulation. to protect the boiler an over heat stat may have tripped. See if you can find any reset buttons on your boiler.
Sometimes you can remove the 'guts' of the tap and just fit new 'guts' inside the old body. this would mean you don't need to worry about pipe sizes etc. often worth reseating the original seating to ensure the water turns off fully afterwards when the tap is closed.
Maybe... one of the taps was left on very slightly... causing water to run down the tap body and around the tap hole into the basin... from where the water ran down the pipe and onto the floor?
It annoys me when taps do this.