Continuity mistake: When Old Bill is wheeled into treatment 3, there's a pillow under his head and the gurney he's lying on has grey trim, horizontal bars under the bed and flat steel plates over the wheels, but when it cuts to inside treatment 3 as he's brought in, the pillow has vanished and the entire style of the gurney he's lying on is completely different.
Inventions - S3-E22
Continuity mistake: When Early and Morton are talking to the cab driver, in the overhead shot there's a hat on the desk, but in the shots facing Early the hat vanishes and other things on the desk rearrange themselves.
Propinquity - S3-E20
Continuity mistake: After the ambulance Roy is riding in is involved in a traffic accident, when Johnny arrives he jumps into the back with the injured attendant and patient, and we can see that the stretcher's footrest is light brown. But when the attendants exit, they carry the stretcher out of the back of the first ambulance then wheel it to the second ambulance, and the footrest is now red. It would seem that they merely transferred the patient from the first ambulance's stretcher to the second ambulance's stretcher while still in the ambulance, but they couldn't have done that because two full size stretchers cannot fit into the back of that first station-wagon style ambulance, especially with attendants back there, so they would have had to do the patient transfer on the ground outside. Hence the problem.
Continuity mistake: When Brackett tells Morton that he can go keep Early company while he awaits test results, Brackett's wearing a patterned tie, and when Brackett walks into treatment 3 his tie is tied differently.
Continuity mistake: When Chet is being timed while putting on his gear, Squad 51 is parked much further up than the engine, providing more room in the apparatus bay behind the squad to run the drill. Then when Station 51 is dispatched to the explosion, the squad's parked normally. Additionally, we see the front bay door is closed, but that's impossible considering how far up Squad 51 was parked during the drill.
Continuity mistake: After John spots a cute nurse talking to Dixie, when he zeros in on Dix for the nurse's name Dixie's holding a pad in her left hand, but in the next closeup her left hand's empty as she gives John an entire run-down on that nurse.
The Promise - S3-E11
Continuity mistake: When Richard jumps out of Rampart's 6th floor window, the bottom of his feet are very filthy (impressive for someone in bed in a catatonic state), but when he wakes up while lying on the ledge and Johnny tries to control him, Richard's feet are now pretty clean.
Continuity mistake: When Engine 51 gets the run in the middle of the night, Johnny's so tired that he stands on Engine 51's tailboard half asleep, and as it rolls out of the bay and makes a right turn, Roy shouts out to him that the run is not for them. There are two problems with this. The entire back of Engine 51 is different between the closeup and wide shot - the surface, the lights, the license plate area, etc. Also, the engine makes a right turn out of the bay, but Roy's looking out towards the left while he's shouting, as if the engine's turning left.
Continuity mistake: At the start, when Johnny and Roy get back to the station from their run, Roy leaves two cabinet doors wide open when he gets two coffee cups, but in the next shot as he shakes Jason's hand, those two doors are suddenly closed.
Continuity mistake: During boat rescue, when Johnny's on the Biophone with Rampart, right after Brackett tells them to continue oxygen and maintain D5W IV, Roy has his hand out with the IV bag and tells 81's guy to hold it, but in the next shot 81's guy is taking a BP cuff from Roy's hand, not an IV bag.
Continuity mistake: While climbing the tower to rescue the "man" at the top, after Johnny slips and slams into the cross beam, when he and Chet are heading back down the tower, the two lights attached to the tower keep switching from the right side to the left side, depending if it's a closeup of them or a wide shot of their doubles. Additionally, in the closeups the lights are large and round, but in the wide shots one of them is a small square.
Continuity mistake: After Station 51 is dispatched to 'man down' and realize it's Old Bill when they look through the window, when Roy and Johnny climb through the window their gear is handed in to them, and John takes the drug box with his left hand and Biophone with his right, but in the next interior shot John's taking them with the opposite hands.
Continuity mistake: In the courtroom, when the patient goes into V-fib, in the two wide shots while Roy is defibbing the patient, John's holding a tube of conductive gel (for the paddle electrodes), but in John's closeup when he says, "Hit him again," John's hands are empty.
Continuity mistake: When Johnny and Roy walk into the courtroom, Johnny places the drug box on the table with its back facing out, but in the closeups of Johnny and the young lawyer, the drug box is turned the opposite way, with its front facing out.
Continuity mistake: When Roy and Johnny walk into the courtroom, Johnny and the young lawyer kneel down beside the patient's right side, but in the patient's closeup Johnny's kneeling on the opposite side of the resuscitator, near the patient's head, where Johnny will walk to a few shots later, when that young lawyer will once again walk over and kneel down.
Heavyweight - S3-E5
Continuity mistake: When the little boy who received an electric shock is brought into the ER, in the shot from the hallway he's taken into treatment 4, which is beside the nurses' station, but in the next shot from inside the room, we can see treatment 2 on the opposite side of the hallway, which is next door to treatment 4. This means they're actually in treatment 1, not 4.
Propinquity - S3-E20
Continuity mistake: The cut that Roy receives over his eyebrow during the traffic accident changes characteristics, such as when he and John are at the poker game, it looks considerably better in following shots, then it looks much worse again.
Continuity mistake: When Deke comes into the ER with the two burned firemen and speaks to John and Roy, the window behind them is on the same side as the ER's receiving entrance. Notice that outside the window there's one of those blue metal shades at the top, which does not exist in the exterior shots of that side of the ER.
How Green Was My Thumb? - S3-E17
Continuity mistake: When Roy and John are with the man who has a live grenade in his belly, they're given flak vests. During this scene frayed material on the long horizontal seams, both at the front and on the back of John's vest, suddenly appears, disappears, reappears and disappears again.
Inventions - S3-E22
Continuity mistake: When Chet's wearing his suction cup shoes, John uses the hose to wet the area around Chet's shoes, and then places the hose down on the ground, but in the shot from inside the van John's still holding that hose.
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.