The Wedsworth-Townsend Act - S1-E1
Visible crew/equipment: During the factory fire, the Battalion Chief tells dispatch over the HT, "Fire through the roof, send me a third alarm," then in the next shot we see Engine 36 arrive, and when the engine comes to a full stop we can see two tripod lighting rigs and stacked film canisters, at the right of the screen.
Visible crew/equipment: When Chet, Roy, and Johnny are with the mother and child at the scene of the vehicle accident, the reflections of location set array lights, four side-by-side reflector screens with some crew members holding them and the camera/cameraman are all visible in the window and surface of the funeral home hearse, as it arrives and then pulls to the side of the road.
Continuity mistake: When Johnny, Roy, and Captain Stanley are rescuing the people trapped inside Olive View Hospital, they are wearing distinctively marked SCBA tanks on their backs, and when all three firemen exit the doorway, Cap is wearing an entirely different tank, and the tanks that Johnny and Roy are wearing have been switched. Then when Johnny jumps off Engine 82, his tank differs again, and when he walks over to the Battalion Chief it's changed yet again.
Visible crew/equipment: When Engine and Squad 51 are at the cliff with the young unconscious boy, Captain Stanley calls in to dispatch, with Stoker standing beside him. The reflection of the camera crane and location set lights are visible in the side door mirror.
Continuity mistake: When Johnny is writing the 'for sale' sign about his Land Rover, in the wide shot the two phone numbers begin with "853" and "352", but in the closeup a piece of paper has been glued over the phone numbers, and the new numbers now begin with "321" and "749."
Pressure 165 - S5-E7
Other mistake: When Johnny prepares Chef Michel's recipe, he leaves the casserole dish in the oven while Station 51 is dispatched to the structure fire. When he and Roy return, Johnny opens the hot oven door to find it smoking and the dish bubbled over, and even though the oven door is supposedly very hot, Roy places his hand on the inside of that door and actually leans on it like there's absolutely no problem.
Propinquity - S3-E20
Visible crew/equipment: At the abandoned refinery, just after Roy attempts to pull out the man pinned under a tank, but is unsuccessful the first time, when it cuts to Captain Stanley and Chet, who are on the third level hosing the fire through the doorway, at the left of the screen a crew member is visible, watching them.
Visible crew/equipment: When Roy and Johnny leave Rampart and are heading back in the squad, about 16:40 minutes in, as they are discussing whether Roy has told his wife about house hunting, you can see two signs on the ceiling of the squad's cab. The signs say 'Emergency Saturday 8PM Rehearsal Mark VI Prod'. Possibly they are magnetic signs for the squad doors so people don't mistake the squad for a real fire department vehicle? (00:16:20)
Continuity mistake: When Brackett asks Early and Morton to assist with the examination of the hallucinating veteran, in the shot from the hallway the doctors walk into treatment 1, its door has no window, but when it cuts to the shot from inside the room, its door has a window, which means they're all in treatment 2 or 3, not 1.
Visible crew/equipment: When Roy and Johnny climb up the open drawbridge, just as they reach the top and see the car dangling off the edge, when Roy says "Boy," the second cameraman is visible behind Roy sitting on the bridge.
The Wedsworth-Townsend Act - S1-E1
Other mistake: At the very start, when the camera moves through Station 10 while the guys are asleep upstairs, we see one of the engines has license plate E111196, but en route there's a closeup of Rescue 10 and its license plate is also E111196.
School Days - S2-E14
Revealing mistake: While 51's on scene at the traffic accident involving a car that broadsided an ambulance, when Chet opens the back door of the overturned ambulance the license plate reads "99923U" but the "U" is lopsided and pushed to the edge of the plate, which makes it obvious that it's a magnetized letter. It's positioned properly in following shots.
Continuity mistake: In the bookmaker's apartment, while Roy. John, Marco and Chet are working on the bookie who's in full cardiac arrest, Vince walks in and speaks to Captain Stanley. Then Vince, who's wearing a watch and ring on his right arm/hand, reaches for all the ringing telephones, and one by one he removes the receivers from the bases, but the right arm/hand in the closeup has no ring or watch.
Visible crew/equipment: At the scene of the scaffold accident on the side of the building, near the top of the crane, there is a small covered booth that hangs from the crane. We can see the reflection of the hidden second cameraman and his camera in the mirrored windows of the building, as he leans in and out of that booth to film some of the footage we see during this scene.
Fair Fight - S6-E5
Continuity mistake: When Johnny and Roy are in the ER after the cave-in rescue, while they're talking to Dixie and Brackett, we can see how long Johnny's hair is. After they get back to the station, when the guys decide to name the dog Henry, there's a closeup of Johnny and now his hair is much shorter and even layered at the sides. Additionally, the dirty areas on his shirt change.
Visible crew/equipment: When Roy and John are in The Boat with the victim of the explosion, the ambulance arrives and just as it passes by we are able to see a nice reflection of crew members, location set's 9-bank array lighting, reflector screens, a ladder and other equipment.
Visible crew/equipment: When Dixie tells the attendants to wheel Ruthie, the woman who went berserk at the salon, into the treatment room where Dr. Early's waiting, there are two T-marks visible on the floor at Dixie's and Johnny's feet.
Continuity mistake: When Johnny and Roy are heading to the parade in The Old Engine, and get sidetracked dealing with a fire rescue, they are wearing the old-style shirts with a ten-button, square bottom bib front, with five buttons on each side. When Captain Stanley laughs at them on the roof, their shirt style differs in the close-up, it's now a nine-button, pointy bottom bib, with four buttons on each side and one button at the bottom point.
Fair Fight - S6-E5
Visible crew/equipment: At Rampart, when Dr. Bracket, DeSoto and Gage are discussing the Hubbards while walking down the hall, two T-marks become visible on the floor behind them when they turn the corner.
Visible crew/equipment: When Roy and Johnny are with 110 and are on scene at the downed airplane, as they remove the pilot from the aircraft, the silver fire starting canister used for the stunt is visible under the plane, before it becomes engulfed in flames.
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.