Heat out: look at the thermostat setting and the breaker or service switch before anything else — midnight calls end there more often than anyone admits. Restart the boiler exactly once; if it faults again, leave it alone. In a high-rise or garden building, check whether neighbors lost heat too: a whole-building outage and a single cold apartment are different emergencies, and the screening needs to know which one it’s routing.
Water coming out: if you can safely reach the feed-water shutoff, close it so the leak stops getting fed, then cut power at the boiler’s service switch. In a mixed-use building, tell the ground-floor business right away — water doesn’t stop at the restaurant ceiling. Then call and describe where it’s coming from.
Gas smell: don’t touch switches, don’t restart anything, don’t go looking for the source. Out of the building, gas utility or 911 from outside, us after the all-clear. That order doesn’t bend.
CO alarm sounding: everybody out, 911, no going back in to look at the boiler. People first, equipment later.