Other mistake: After Roy has found the location of the boy trapped in the collapsed building, Captain Hammer gets on the handy-talkie and says "Engine 51, Stoker," but oddly enough the subtitles read, "Agent 51, Stoker." Subtitles from Universal Studios 2010 DVD.
Continuity mistake: When Station 51 is dispatched to 'the man down' at the hotel, Roy gets into the squad fully dressed (he was talking to Chet) and wearing his blue uniform shirt, but when they're in the apartment his shirt is gone and he's only wearing an undershirt under his jacket, though Johnny is wearing his uniform shirt.
Pressure 165 - S5-E7
Continuity mistake: While Johnny and the doctor are in the pressurized chamber with the diver, the guy outside the chamber tells them that they're at 165 and vetting, as he holds the mic up to his mouth with his left hand, but when it cuts to the interior shot, the mic is held up in his right hand.
Other mistake: When the dispatcher drops tones for the structure fire, he calls on Station 51, Engine 27, Engine 32, and Truck 105. Once there, Captain Stanley tells the dispatcher to send a second alarm, then hear him call on Station 19, Truck 98, Truck 34, and Battalion 43. However, the only ones at the fire with 51 are Engine 9, Engine 17, Truck 17, and two men with helmets from 20, even though dispatch did not call on any of them, and of all the companies that were called to the fire, none were there, except for 51.
Visible crew/equipment: When Roy and Johnny are with Dixie, they see the new unit and scanner at the base station, and when Roy walks over to it, the actor's white tape mark is visible on the floor where he stands.
Continuity mistake: When Peter staggers into the ER because of insulin shock, Dixie walks down the hallway passing treatment rooms 2 and 4, with treatment 2 being beside the nurses' station, and it's the same set-up later when Peter's girlfriend speaks to Dixie in the hallway. However, in prior and subsequent shots of the hallway, it's treatment 4 that's beside the nurses' station.
The Wedsworth-Townsend Act - S1-E1
Other mistake: When Squad 10 is dispatched to the the high-voltage electrocution, Tony opens the bay door, but the closeup we see is actually the same closeup of the hand cupping the switchplate that was shown earlier, when dispatched to the nighttime factory fire.
An Ounce of Prevention - S6-E13
Continuity mistake: At the ferris wheel, when the boy starts to climb down to help the man in the lower seat, in the closeup he steps on the two yellow, fluorescent tube light bulbs causing the bulbs to plummet and shatter on the ground below. The problem is that those two fluorescent bulbs did not even exist in the prior wide shots, that lamp socket space was empty.
Visible crew/equipment: When Johnny chases Harriet down the street, behind Johnny we see Roy backing up the squad to follow them, with nobody around, then when it cuts to the view from within the squad, the reflection of crew is visible in the driver's side mirror.
Visible crew/equipment: When Roy gets the little girl, Angie, out of the wrecked airplane and then places her in the Stokes basket, the outlines of the mic transmitter and wire are visible on the back of his shirt.
Visible crew/equipment: When Brackett, Dixie and Early are working on the unconscious little boy, once Brackett says to go with the pacemaker, multiple black T-marks are visible all over the floor - three under the gurney and one near the cart. Another actor's white tape mark is visible under the gurney (partially blocked by the green oxygen tank), where both Early and Dixie stand at different times.
Fair Fight - S6-E5
Visible crew/equipment: After the cave-in rescue, when Dixie, DeSoto and Gage are in the ER, Gage washes his face and as he comments that he wasn't cut out to be a mole, two tape marks are visible at his feet.
Visible crew/equipment: When Mr. Grady (self-defense instructor) is in the ER, being examined by Dr. Brackett, there is a visible T-mark on the floor behind Gage.
Visible crew/equipment: After Chet is brought to the ER, Gage goes to the nurses' station. When Brackett opens the door and walks out of the base station booth, the actor's T-mark is visible on the floor behind him.
Welcome to Santa Rosa County - S6-E10
Continuity mistake: When getting the climbers off the mountain, the Ford letters on the tailgate are muddy and blanked out, but are not in the scenes where they're transporting the climbers in the pickup bed.
Visible crew/equipment: When Brackett's helicopter takes off the filming helicopter can be seen through the window. (00:03:45)
Continuity mistake: Just before the opening credits both Engine 51 and Squad 51 are inside the station. The alarm goes off and when Squad 51 leaves the station Engine 51 has vanished.
Daisy's Pick Blind Date - S4-E7
Other mistake: When Squad 51 is dispatched to "man needs assistance", in the exterior shot as the squad rolls out of the apparatus bay we can see Engine 51 still inside the bay, but the real Station 127's engine is parked right beside the station house.
Continuity mistake: When Roy and Johnny are on the roof with Harriet, we can see the shadow being cast by the utility pole on the street down below, and when the police car shows up moments later that shadow has changed significantly. (00:12:40)
Visible crew/equipment: When squad 51 parks upon arrival at the gas station the array lighting is visible on the driver's door.
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.