Audio problem: When Gordon backing down to the bottom of the hill, you can hear brakes screeching, but Gordon's wheels are still moving.
Continuity mistake: When Edward is pushing trucks over a turntable, when he stops, he is very close to the trucks, when the camera changes, he moves back a bit. (Note the tank the Fat Controller is standing on).
Continuity mistake: When Thomas teases James about bootlaces, the background disappears in a close up of Thomas.
Continuity mistake: When Gordon says "Yes, I will" the background disappears between shots.
Revealing mistake: At the end, when Thomas backs some coaches into the station, he starts moving after 3 seconds the camera starting rolling.
Revealing mistake: When Thomas passes the leveling crossing for a second time, the cars at the crossing have no drivers.
Revealing mistake: When Thomas goes back to the station to try again from the signal, when he starts, the steam is coming from the track and not from Thomas.
Revealing mistake: When Thomas passes a yard with a black car and a red car, you can see tyre marks on the ground from previous takes.
Revealing mistake: Just before Thomas goes over The Switch, his left eye is uneven and then when he crosses The Switch, it readjusts itself.
Other mistake: When the Fat Controller is talking to the crew, the buffers on the first coach in front of Thomas is crooked.
Visible crew/equipment: When the porter bangs the door, a light-stand is briefly reflected on the window of the door.
Revealing mistake: When Thomas leaves the sheds, his driver doesn't have a face.
Visible crew/equipment: When Henry is ill, one of the lights behind Henry is not one of the ones from outside, it's a studio light.
Other mistake: When Thomas is grumping, his lamp is dirty, even though he didn't do anything dirty yet.
Revealing mistake: At the beginning of the episode, the end of the set is visibly reflected of Gordon's smoke box in a close-up of Gordon.
Continuity mistake: When the engines are laughing at Thomas, Henry's eyes are wonky.
Factual error: At the beginning, the first shot of the episode, you can see cranes in the back of the station. They only have cranes at the harbor, not at stations.
The Runaway - S2-E10
Audio problem: When Thomas is tired and approaching the station, he is moving pretty slow, but the sound of Thomas' wheels moving is like he's going pretty fast.
The Runaway - S2-E10
Visible crew/equipment: When Harold is flying, in one shot, a stage light is reflected off his blades.
The Runaway - S2-E10
Revealing mistake: When Thomas' fireman is ill, you can see a brief flash of red outside, meaning it's James. (Note: same footage from Old Iron).
Answer: He was in the water.