B767 Captain reported numerous delays were caused by mechanical; communications and ground weather. The flight eventually cancelled and the Captain called out fatigued due to the situation.

Narrative

Reported to ZZZ; Date; XX:30; H3005. OAT at one time was discussed to be as high as 107 degrees F. Met FO (First Officer) at FPA (Flight Planning Area) and completed flight planning assignments. Proceeded to Gate XX and prepared aircraft for on-time departure of Aircraft X. Main cabin door and cargo door closed...was waiting for Final DG report. Called ZZZ Operations about Final DG...no report. Sent Load Planning a message and called Dispatch regarding no Final DG Report...Final DG report arrives about 15-20 minutes after doors closed. (Note: very hot on flight deck; estimate of 95 degrees F.) Push the aircraft; start both engines; and taxi to XXL/WW.Given instructions to line up and wait. Once on the active runway; Equipment Overheat EICAS message. Obtained clearance to taxi clear of Runway XXL. Initiated QRH procedures; switch to Standby; wait 5 minutes to determine if Overheat condition still present. Once switched to Standby; overheat annunciation inhibited for 5 minutes. After 5 minutes overheat still present. Contacted ZZZ Operations and asked for a gate return. Was told no wide body gates available; did you call Maintenance? Maintenance release sent. ZZZ Operations instructed me to contact ZZZ Maintenance. ZZZ Maintenance asked to confirm the operating configuration of the aircraft and I confirmed. ZZZ Maintenance asked me if I wanted to reset the system. I declined the request. I again asked ZZZ Operations for a gate; no gate available. (Note: flight deck temperature estimated in excess of 100 degrees F. QRH discussed failure of instruments; due to excessive heat. I was concern for safety of flight deck occupants and possible damage to the aircraft.) Contacted Dispatch and explained the situation. Dispatch called ZZZ Operations and eventually Gate XX was assigned for gate return.Shortly after parking at XX; ZZZ Tech Operations Personnel arrived on the flight deck and showed me an iPad picture of a closed E and E bay exhaust valve. Tech Operations indicated that the exhaust valve was not modulating open. Deplaned passengers from aircraft. At first; Tech Operations wanted to MEL the malfunctioning exhaust valve. I indicated I would not operate the aircraft with the MEL. Tech Operations then stated that they would replace the exhaust valve. Tech Operations indicated that the repair would be complete by XE:15pm. At approximately XE:30pm; I was notified of an aircraft swap. FO and I proceeded to the FPA; I reviewed and authorized a new release; and proceeded to Gate XY. At some point; I received a call from Crew Scheduling and was asked if the flight deck crew was willing to extend IAW FAR 117. The FO and I were willing to extend. CCO XH:28.pm.To continue; storm developed around ZZZ; with associated lightning...Ramp Closed. Ramp opened around XG:00pm. The flight began boarding. We started taking on the required fuel and I was confident the flight would takeoff prior to CCO Time. At approximately XG:50pm; I noticed that the cargo door was closed; but did not receive a DG report; main cabin door closed. I sent a message via Chat and asked about the DG report and asked to confirm that baggage loading was complete. After a several minutes it was reported that baggage cans from the previous flight were still on the previous aircraft and that baggage cans for that flight had not been loaded. ZZZ Operations announced that the flight was cancelled. Passengers deplaned. The FO and I left the aircraft at approximately XH:30. Crew Scheduling called and left a message that Aircraft X would operate/depart Date1; XR:30 am. I got home at approximately XJ:15am; Date1; and into bed at approximately XK:00 am. Prior to bed; I took 3 Bayer aspirins; as I had a significant headache. I estimate that I fell asleep at approximately XL:00 am. My alarm clock was set for XO:30 am. Once awake I determined that I was fatigued and was not fit for duty. I called Crew Scheduling and reported fatigued. The scheduler requested a time when I would be fit...I responded mid to late afternoon on Date1. I woke up at approximately XS:30 am; and called Crew Scheduling advising them that I was no longer fatigued.I would like to add that I believe my prolonged exposure to much higher-than-normal ambient temperatures added to my state of fatigue.