If your tank fed Londinium is beeping, it probably thinks the water in the tank/reservoir is low. (It also beeps if filling the boiler takes rather long. In that case switching off and on sorts that.)
Possibly the water filter took out too much minerals so the water is not conductive to electricity. In that case add unfiltered water.
Also possible: the tiny metal nipple inside the bottom of the reservoir has been pushed up a little and is not connecting to its contact below it. Push the metal 'nipples' back down to be flush with the plastic and you should be good.