Check the obvious first: thermostat set to heat and calling, breaker not tripped, and — on oil — the tank gauge above empty. On gas, look for a lockout light and note it; do not keep pressing reset. On oil, one reset is the test — if it does not fire, stop resetting, because repeated resets flood the chamber with unburned oil.
Protect against freezing: if the house is dropping toward freezing and help is on the way, open cabinet doors under sinks on exterior walls, let faucets drip slightly, and keep interior doors open so what heat remains circulates. In a seasonal shore home, do not fire a boiler on a system that may have freeze damage — wait for the pro to check for split pipes and a cracked block first.
Do not: run space heaters unattended, thaw pipes with an open flame, or enter a basement with standing water around electrical equipment. If water is actively flowing from a burst pipe, shut the main water valve if you can reach it safely.