Should I pay an extra charge to fix airlock?

Hi I recently paid for my boiler to be relocated as part of a new kitchen installation. There was an airlock which from memory took the plumbers roughly an hour to fix. Should I pay extra for this? Or should I expect for it to be a common thing that a plumber would account for in a fixed price? I wasn't notified about the extra cost at the time. It came up when he sent the bill weeks later.