Gas or Exhaust Smell from a Tankless Water Heater

If you smell gas

Leave the building. Call your gas utility from outside.

Not after checking the heater. Not after turning it off. Natural gas and propane are odourised precisely so that this is the signal, and the response is designed to need no judgement:

• Do not restart the unit, and do not turn it off either — operating any switch can produce a spark.
• Do not use light switches, doorbells, garage door openers, or a phone inside the building.
• Do not look for the leak.
• Get everyone out, including pets, and leave the door open behind you.
• Call the gas utility or 911 from outside, or from a neighbour’s.

Propane is heavier than air and settles low — in a basement, a crawlspace, a stairwell. If your unit runs on propane and the smell is downstairs, treat it as more serious rather than less.

If you smell exhaust

A burnt, sharp or acrid smell indoors near the heater, or a smell like something scorching when it fires, is a different fault with the same seriousness. It means combustion products may not be going where they should.

Carbon monoxide has no smell. That is the whole problem: what you can smell is not the dangerous part, it is the warning that the dangerous part may be present too. Headache, nausea, dizziness or drowsiness in more than one person in the building — or in a pet — is a medical emergency, not a plumbing one. Get out and call emergency services.

Otherwise: turn the unit off if you can do so safely, ventilate, leave, and call a licensed professional. Do not run it again until someone has inspected the venting.

Every home with a gas appliance should have a working carbon monoxide alarm. If yours is more than a few years old, it has an expiry date printed on it.

Why this page has no DIY steps

Because there are none worth publishing. Every fault behind these smells — a leaking connection, a cracked heat exchanger, a disconnected or badly sealed vent joint, exhaust recirculating back into the air intake — needs instruments and a licence to diagnose, and getting any of them wrong has consequences that are not financial.

The manufacturers agree, and their own documentation is blunt about it. Rinnai’s vent instructions warn that a joint assembled without the specified lubricant can leak exhaust gas. Every code on this site involving gas, ignition, venting or exhaust carries one verdict — call a professional — and no steps at all where the severity is highest.

After the utility has been

Once the gas company has made the site safe, the repair is still ahead of you, and it is worth going into it knowing what the code said. If the unit was displaying one, look it up — it will tell whoever comes out which circuit to start with.

• Rinnai error codes
• Navien error codes
• Rheem error codes
• Takagi error codes

What we will not do is give you a way to get the hot water back on in the meantime.