How Scale Damages a Tankless Heater
Scale is mineral deposit — mostly calcium and magnesium — that builds up inside the heat exchanger as water is heated. Greater Vancouver's water is relatively soft compared to many regions, which slows scale formation, but it does not stop it entirely, especially in homes with water softener bypass, well water, or many years between flushes.
As scale accumulates, it insulates the exchanger walls, forcing the burner to work harder and run hotter to deliver the same hot water. Over time this overheating stresses the metal, narrows internal passages, reduces flow, and can eventually crack the heat exchanger. A scaled unit also throws maintenance or overheat codes and loses efficiency. Descaling (flushing the unit with a descaling solution) is the maintenance step that removes this buildup before it causes lasting harm — which is exactly why it is recommended periodically.
Why a Leak Can Appear During or After Descaling
Sometimes a tankless heater starts leaking during a flush or shortly after, and it feels like the descaling caused the problem. Usually, descaling did not create the weakness — it revealed it.
When a unit is heavily scaled, the deposits can partially plug a hairline crack or seal a marginal connection, masking a leak that was already developing. Flushing dissolves that scale and removes the temporary plug, so water finds the existing fault and starts to weep. The descaling process also involves opening the isolation valves, connecting hoses, and circulating fluid, which can disturb aged bleeder caps, gaskets, and valve seats that were already near the end of their life. In other words, the leak was coming; descaling simply brought it forward.
Common Post-Descaling Leak Sources
Isolation/service valves and bleeder caps. The most common. These are opened, closed, and stressed during every flush, and worn seats or caps weep afterward. Often a simple, low-cost fix.
Loosened threaded connections. Handling hoses and valves during the flush can disturb an already-loose inlet or outlet fitting.
Revealed heat exchanger crack. If removing scale uncovers a genuine exchanger crack, the unit leaks from the cabinet base — the serious case, where warranty status and unit age determine repair versus replace.
Gasket or O-ring seepage. Older internal seals disturbed by the flush may begin to weep.
Identifying which of these you have requires drying everything, running the unit, and tracing the source — and if it is the exchanger, that calls for professional diagnosis.
Prevention and Professional Descaling
The best way to avoid scale-driven leaks is regular professional descaling combined with healthy seals and valves replaced when they show wear. A technician descaling your unit will also inspect the valves, condensate system, and connections, catching marginal parts before they fail rather than after. For homes with harder water sources, an inline scale filter or treatment can extend the interval between flushes.
Tankless water heaters are serviced by our parent company, CanroHeat, which performs proper descaling and replaces worn service valves and gaskets at the same visit so a flush does not turn into a surprise leak. If your unit is already leaking after a descale, we will trace the source — valve, fitting, gasket, or exchanger — and tell you honestly what it needs. Descaling and valve replacement costs fall in a modest range; call CanroHeat at 604-359-1081 for an exact quote and to book service across Greater Vancouver.