No heat with temperatures near or below freezing is the clearest emergency. Fitchburg's older housing — triple-deckers, mill-worker two-families, drafty Victorians — loses heat fast, and frozen pipes turn a no-heat call into a water-damage call within hours. If the thermostat is dropping and the boiler will not stay running, that is a 24/7 call, whatever the hour.
The next tier is fuel safety: an oil tank or fuel-line leak, the smell of heating oil pooling in a basement, or a burner that keeps trying and failing to light. Oil leaks do not get better overnight, and an aging tank in a Fitchburg basement can fail suddenly. Report it as a leak first on the call so it is prioritized correctly.
What is not a middle-of-the-night emergency: a boiler that heats fine but sounds different, a slow pressure drop you noticed weeks ago, or no-heat in a shoulder season when the house is holding temperature. Those still deserve a prompt call — the diagnosis page covers them — but they do not need to jump the queue ahead of someone freezing.