Freeze damage to a tankless unit's internal passages usually shows up as a leak or no-heat fault once temperatures rise again after a cold snap.
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Freeze damage to a gas tankless water heater happens when water left inside its internal passages freezes and expands, which can crack the heat exchanger or other internal components. It's most likely on exterior-wall installations during a cold snap without adequate freeze protection, and it usually isn't obvious until temperatures rise and the unit either leaks or fails to heat at all. Whether it's repairable depends on which components cracked, since a damaged heat exchanger specifically is often not cost-effective to replace compared to the unit's overall value.
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Many gas tankless water heaters are installed on exterior walls specifically because that's where venting is straightforward, but that same location exposes the unit's internal water passages to outdoor temperatures more directly than an interior mechanical room would. Most tankless units include built-in freeze protection, typically a small heating element and sensor that activates in cold conditions, but that protection depends on the unit having continuous power and, in many cases, the gas supply still connected. A power outage during a cold snap, or a homeowner shutting off power or gas without realizing the implications, can disable that protection at exactly the moment it's needed most.
Metro Vancouver's climate rarely sees extended deep freezes, but a cold snap combined with wind exposure on an exterior wall can still bring temperatures low enough, especially overnight, to freeze water inside an unprotected or unpowered unit.
| Symptom | Likely cause |
|---|---|
| Water leaking from the unit after a cold snap | Cracked internal component from frozen, expanded water |
| No hot water at all after a freeze event | Cracked heat exchanger or blocked internal passage |
| Error or lockout code appearing after cold weather | Internal sensor detecting an abnormal condition from freeze-related damage |
| Visible ice on or around the unit itself | Active freeze in progress, often before full damage has occurred |
Because internal cracking isn't visible from outside the unit, freeze damage is often only confirmed once a technician opens the unit and pressure-tests or visually inspects the heat exchanger and internal lines.
If freeze damage is limited to an external fitting, valve, or a component that's straightforward to replace on its own, a targeted repair is often reasonable. If the heat exchanger itself has cracked, which is the component most directly exposed to trapped water, replacing it can be a significant cost relative to the value of an aging unit, and in that situation full replacement is frequently the more sensible path rather than investing heavily in a single major component repair. A technician assessing the damage can give you a realistic comparison of repair cost against the unit's remaining expected life before you decide.
Built-in freeze protection is a helpful feature, but it isn't a substitute for a proper drain-down if the home will be unoccupied and unheated during an extended cold period, since that protection still depends on continuous power.
If you notice a leak, no hot water, or an unusual fault code after a cold snap, shutting off the water supply to the unit and calling for a technician to assess the damage is the right first step, rather than attempting to restart or repeatedly reset the unit yourself. Repeated restart attempts on a unit with a cracked internal component can sometimes worsen a leak or push water into places it shouldn't be.
Safety note
Any inspection, repair, or replacement of a tankless water heater's gas connection, venting, or internal components must be performed by a Technical Safety BC licensed gas fitter. If you ever smell gas or suspect a carbon monoxide issue, leave the home immediately and call FortisBC at 1-800-663-9911.
Common signs include a leak, no hot water, or a fault code appearing after a cold snap. Because internal cracking isn't visible from outside, a technician usually needs to inspect the unit to confirm.
Built-in freeze protection helps significantly, but it depends on continuous power and, in many cases, gas supply, so it can fail to protect the unit during a power outage or if the supply is shut off during cold weather.
Sometimes, but replacing a heat exchanger is often costly relative to the value of an aging unit, so full replacement is frequently the more practical choice depending on the unit's age and condition.
It's better to shut off the water supply and have a technician assess the unit first, since repeated restart attempts on a damaged unit can sometimes worsen a leak.
It's not common given the generally mild climate, but exterior-wall units without proper freeze protection or continuous power can still be affected during a cold snap, particularly with wind exposure.
Yes, a proper drain-down removes the water that would otherwise be at risk of freezing, which is a more reliable protection than relying on built-in freeze protection alone during an extended unheated absence.
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