This aircraft appears to be suffering yet more bad luck.
Having been rescheduled as UA2056 with a departure time of 09:00, followed by a delay to 13:55, the aircraft appears still to be on the ground at 14:10.

Airborne at 10:49. Should be landing at Newark in a couple of hours time.

Fuel jettison is only an option on the 767. Same with the A330, not all of them have it. Overweight landings require thorough inspections afterwards, and may result in damage to the gear and fuselage. Makes sense to burn up the fuel in a hold rather than risk a huge repair bill if it's nothing urgent.

Spotted that Dave. It seems my earlier info was inaccurate. Currently bimbling along over Nova Scotia.

Well this proves the airplane had fuel dump capability and that it was working so still doesn't explain why it was airborne for nearly 4 hours??????

United Airlines flight spends four hours circling the English Channel | Daily Mail Online

Might have been waiting for an available slot. LHR usually only take unscheduled arrivals or give priority to aircraft that declare an emergency. Maybe UA didn't want all that paperwork 😂