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What to do if…
your boiler or furnace is leaking water and the situation is getting worse

Produced and maintained by PanicStation.org Published: Last reviewed: Editorial policy USA guide

Short answer

If you smell gas, have symptoms that could be carbon monoxide exposure, or a carbon monoxide alarm is sounding, leave the building first and call 911 from outside. Otherwise, shut the system off if you can do that safely, keep water away from electrical hazards, and call a licensed HVAC technician or plumber.

Do not do these things

  • Do not keep running the furnace or boiler to see if the leak stops.
  • Do not open sealed panels, remove covers, or put your hands inside the unit.
  • Do not touch outlets, cords, breakers, thermostats, or the unit’s power switch if you are wet or standing in water.
  • Do not step into water to reach a breaker, shutoff, valve, or switch.
  • Do not stay inside if you smell gas, hear gas leaking, or a carbon monoxide alarm is sounding.
  • Do not use switches, lighters, appliances, or a phone inside the building if you suspect a gas leak.

What to do now

  1. Deal with gas smell, possible carbon monoxide symptoms, or a carbon monoxide alarm first.

    • If you smell gas, hear gas leaking, feel symptoms that could be carbon monoxide exposure, or a carbon monoxide alarm is sounding, leave the building immediately.
    • Get everyone to fresh air.
    • From outside or from a neighbor’s location, call 911 and/or your gas utility’s emergency number.
    • Do not go back inside until emergency responders or the utility say it is safe.

  2. Turn the system off if the area is dry enough to do so safely.

    • Set the thermostat to OFF.
    • If you can reach it without standing in water, turn off the furnace or boiler service switch.
    • If water is spreading toward electrical equipment and you can reach the breaker from a dry, safe position, turn off power to the HVAC circuit at the breaker.
    • If reaching any switch or breaker would mean stepping in water, leave it and call for help.

  3. Stop obvious water feeding the leak only if you already know the valve.

    • If there is a whole-home humidifier attached to the furnace and you can clearly identify its small water supply valve, close that valve.
    • If you have a hot-water boiler and the boiler feed valve is clearly labeled or already known to you, you may close it to limit more water entering the boiler.
    • Do not force stuck valves, guess at unlabeled valves, or keep trying if anything feels unsafe.

  4. Limit damage without getting near electrical hazards.

    • Put a shallow pan or bucket under the drip if you can place it safely.
    • Use towels to slow water spread away from outlets, extension cords, stored items, and the unit’s controls.
    • Keep children and pets away from the wet area.
    • Move dry belongings away from the leak if you can do it without touching the unit or electrical items.

  5. Call for urgent repair using clear words.

    • Tell the company: “Active water leak at furnace, air handler, or boiler; leak is getting worse; system is shut off; water is near electrical items if applicable.”
    • Ask whether you need an HVAC technician, a plumber, or both.
    • If you rent, notify your landlord or property manager immediately and say you shut the system off to reduce damage.

  6. Take quick photos only after the safety steps.

    • Photograph where the water is dripping from and where it has pooled.
    • Note whether the unit has white PVC venting, a condensate pump, a whole-home humidifier, or visible boiler piping.
    • Stop documenting if the leak, gas smell, alarm, or electrical risk gets worse.

What can wait

  • You do not need to identify the exact cause before calling.
  • You do not need to flush condensate lines, add chemicals, remove panels, or take the unit apart.
  • You do not need to decide on replacement, upgrades, warranties, or insurance details right now.
  • You do not need to keep troubleshooting if the area is wet, the unit is still leaking, or you feel unsure.

Important reassurance

You have already done the most useful first steps if people are away from gas or carbon monoxide risk, the system is off where safe, and water is being kept away from electrical hazards. The exact cause can be worked out by a qualified repair professional after the immediate risk is controlled.

Scope note

These are first steps to stabilise the situation and reduce immediate risk. Later decisions about repair, replacement, landlord responsibilities, insurance, or safe restart may need specialist help.

Important note

This is general information, not legal, medical, financial, therapeutic, or professional advice. If there is a gas smell, a carbon monoxide alarm, symptoms that could be carbon monoxide exposure such as headache, dizziness, nausea, confusion, or shortness of breath, or water near electrical components, treat it as urgent and contact emergency services or a qualified professional.

Additional Resources

Closely connected guides that may be useful during the same situation or its immediate aftermath.

About this guide

This guide was produced and is maintained by PanicStation.org using its published editorial process. Official and specialist sources are checked where relevant, and AI-assisted tools may be used for drafting, organisation, and consistency checks. The site operator remains responsible for publication, revision, and removal decisions.

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