FirstCheck
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🍁 Conçu pour les foyers canadiens — rédigé selon les codes canadiens et les règles provinciales. N’est pas destiné à un usage hors du Canada.
ÉBAUCHE — cette page n’a pas encore été révisée par un professionnel licencié. Aperçu éditorial seulement.

Tankless water heater: no hot water

A tankless unit that stops making hot water is usually telling you why — most start with a code on the display and an easy first check, not a failed heater.

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In Canadian homes, read the display first. Most tankless units show an error/fault code that names the problem; note it, then power-cycle the unit once (off at the switch or breaker for a minute, back on). A one-time fault often clears. If the same code returns, look it up in the manual — it points you straight at the cause. On a gas unit, if you smell gas at any point, stop and call your gas utility.

Classé selon des données de pannes réelles. L’ordre s’ajuste selon vos observations ci-dessus.

Causes probables, dans l’ordre à vérifier

Ordre typique affiché
Pour débutant Faisable, avec soin Sécurité critique Appelez un pro

visibilityHow to check

warning Hot water and a small spillThe water in the unit can be hot, and opening the inlet screen lets a little out — keep a bucket and a towel handy and let the unit cool if it's just been running. This is a low-risk job on the water side only; do not open any gas or combustion component. If the unit keeps faulting after a clean screen, hand it to a pro rather than forcing it.
  1. Run a hot tap fully open and listen: if the unit fires only at full flow, or a flow/ignition code appears at low flow, the inlet screen or a throttled valve is the prime suspect.
  2. Close the cold-water isolation valve under the unit, then unscrew the inlet water filter/screen (put a bucket underneath — a little water will spill).
  3. Rinse the screen clean of grit and scale, reseat it, reopen the isolation valve, and retest. While you're there, confirm all inlet valves are fully open and check faucet aerators for blockage.
buildadjustable-wrenchbuildbucket schedule15 min

verifiedPourquoi confier ceci à un pro

A tankless unit that won't ignite, won't hold a flame, or is throwing a heat-exchanger fault involves live gas, combustion, and venting — get any of it wrong and you risk a gas leak or carbon monoxide. On a gas unit this is work for a licensed gas-fitter (and on an electric unit, an appliance tech or electrician for the heating side). Leave the covers on and book a pro.

Vos notes accompagnent la demande — ce que vous avez vu, ce que vous avez éliminé, quand ça a commencé — pour que le pro arrive avec une longueur d’avance.

handymanHow to fix it

With the unit powered off and cool, connect a submersible pump and hoses to the service (isolation) valves, circulate a descaling solution (white vinegar or a food-safe descaler) through the heat exchanger for the time in your manual, then flush with clean water and restore service.

  1. Turn the unit off (switch or breaker) and shut the hot and cold isolation valves so no household water flows through during the flush. Let it cool.
  2. Attach hoses from a submersible pump sitting in a bucket to the cold service port, and a return hose from the hot service port back into the bucket. Open only the two service (purge) valves.
  3. Fill the bucket with descaling solution — food-safe descaler or plain white vinegar per your manual — and run the pump to circulate it through the heat exchanger for the time the manual specifies (commonly 45–60 minutes).
  4. Drain the solution, refill the bucket with clean water and flush for several minutes, then close the service valves, remove the hoses, reopen the hot and cold isolation valves, and restore power. Run a hot tap to confirm output.
schedule75 min savings$25–60
Tankless descaling / flush kitPump, hoses, and bucket; use a food-safe descaler or plain white vinegar — check your manual for the approved solution Tankless service valve (isolation) kitOnly if your unit has no service valves; must match the unit's connections — a plumber's job to install
gavel Vérifiez d’abord votre province AB: permis au propriétaire · BC: permis au propriétaire · ON: permis au propriétaire · PE: permis au propriétaire · QC: réservé aux licenciés
Descaling/flushing on the water side is generally owner-permitted; the ignition/flame-sensor/heat-exchanger and any gas or venting work is licensed-only (gas-fitter). Confirm the provincial rule.
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Pourquoi la liste est dans cet ordre

Nous ne classons pas seulement selon la probabilité. Nous classons comme le ferait un bon artisan honnête : éliminer d’abord les causes gratuites, sûres et courantes. C’est pourquoi les vérifications peu coûteuses passent avant les réparations chères — et pourquoi tout ce qui est dangereux reçoit un arrêt net plutôt qu’un encouragement. Cet ordre existe pour vous faire économiser, pas pour vous vendre quelque chose.