Short answer
If you smell gas near your boiler, do not try to find the leak or restart the boiler. Leave the building, avoid operating electrical switches, and call your gas utility's emergency line or 911 from outside. Only re-enter when professionals say it is safe.
What to do immediately
1. Leave. Get everyone out of the building by the nearest safe exit. Do not stop to open windows on your way — leaving quickly matters more.
2. Do not touch electrical switches. Flipping a light switch, unplugging something, or using a phone inside can create a spark. Leave phones and electronics alone until you are outside.
3. Call from outside. Once clear of the building, call your gas utility's emergency number or 911. Give the address and say you smell gas near the boiler.
4. Warn others, keep distance. Make sure others in the building know, and keep everyone away from the building until it is cleared.
What never to do
Do not light matches or candles. Do not try to locate the leak yourself. Do not turn the boiler off and back on to "see if it clears." Do not re-enter to grab belongings. A gas odor is one of the few boiler situations where the right move is entirely about safety, not diagnosis.
Rotten-egg smell versus other odors
Natural gas is odorless; utilities add the rotten-egg smell (mercaptan) precisely so leaks are noticeable. But not every odd smell near a boiler is gas: dusty burning smells on first fall startup, musty basement odors, and oil-burner smells are different problems. If you are unsure whether it is gas, treat it as gas — the downside of being wrong in that direction is a false alarm, not an explosion.
After the all-clear
Once the utility or fire department clears the building, the boiler still needs a professional look before it goes back into service. Gas-side faults — valves, connections, ignition, venting — are diagnosed under controlled conditions, not by trial and error. For that follow-up, see pilot light and ignition repair in Medford and gas and combi boiler repair in Medford. Describe exactly what happened and what the utility found; that history shapes the diagnosis.
Questions to ask before approving work
Ask what the provider found on the gas side versus the ignition side — the smell and the boiler fault are sometimes two separate issues. Ask whether combustion and venting were checked, not just the leak point. And ask what would have to change for the problem to recur, so you are not paying for the same visit twice.
Related service pages
For gas-system follow-up, see pilot light and ignition repair in Medford and gas and combi boiler repair in Medford. If you currently have no heat for another reason, review emergency boiler repair, and request service when you are ready to describe the issue.