Tankless Water Heater Repair: Restoring Your On-Demand Hot Water

Jack Japuncic • June 6, 2026

Written by the team at KCs Plumbing, Heating & Drain Services · Reviewed by Jack Japuncic, Master Plumber

A tankless water heater is supposed to give you endless hot water, so when it suddenly runs cold or flashes an error code, it's both inconvenient and a little confusing. These are sophisticated units, and that can make a fault feel more alarming than it really is. The reassuring truth is that most tankless problems are repairable, and a fair number turn out to be maintenance issues rather than genuine failures.

No hot water from your tankless unit? Call KCs Plumbing & Heating at (604) 873-3753. Our emergency line is open 24 hours a day across the Lower Mainland.

What the Symptom Is Telling You

An error code on the display. Tankless units are good at telling you something is wrong, though the code needs interpreting against make and model, it can point to ignition, flow, venting, or sensor issues.
No hot water or no ignition. Often a gas supply, igniter, or flame sensor issue on gas units.
Hot water that fluctuates or runs cold. Scale buildup, a flow sensor, or a unit working against demand it wasn't sized for can all cause this.
The "cold water sandwich." A short burst of cold between warm stretches, common to the technology itself and sometimes improved with adjustments or a recirculation setup.
Reduced flow or efficiency. Frequently a sign the unit needs descaling rather than a sign of failure.

That last point is worth sitting with, because it changes the whole conversation: a large share of tankless complaints — fluctuating temperature, reduced flow, certain error codes, trace back to scale or a clogged inlet filter rather than a broken component. In those cases the fix is service, not a part, and it's the first thing worth ruling out since it's the cheapest. More on that in our guide to tankless maintenance.

Why This Isn't a Job to Guess Your Way Through

A tankless unit packs a high-output burner or heating element, electronic controls, sensors, and venting into a compact wall-mounted package. Misreading an error code or guessing at a sensor wastes money on parts that were never the problem. And on a gas tankless unit, anything touching the gas supply, combustion, or venting legally requires a licensed gas fitter in BC, the safety stakes are real, not theoretical. We're a licensed gas-fitting company, so the whole repair happens in-house, no subcontracting out the part that actually needs the license.

Repair or Replace?

Because tankless systems are built to last well beyond a typical tank's lifespan, repair is usually the right answer when something goes wrong, especially on a unit only a few years old. Replacement enters the conversation when a unit is genuinely near the end of its long life or has suffered major damage. We diagnose the actual problem and tell you honestly which situation you're in, rather than defaulting to whichever job pays more.

Frequently Asked Questions

Why Is My Tankless Water Heater Not Producing Hot Water?

Common causes include a gas supply or ignition issue, scale buildup, a flow sensor problem, or a clogged inlet filter. Many are repairable or even just a maintenance fix.

Why Does My Tankless Hot Water Keep Going Cold?

Fluctuating or cold water often points to scale, a flow sensor, or a unit working beyond what it was sized for. Descaling resolves a surprising amount of it.

Do You Repair Gas Tankless Water Heaters?

Yes. As a licensed gas-fitting company, we handle gas tankless repairs safely and to code — this isn't work that should be attempted without one.

We work on all major tankless brands, including Navien and Rheem, for both residential and commercial systems. Call (604) 873-3753 or book online and we'll tell you plainly whether it's a five-minute maintenance fix or something bigger, either way, you'll know before we start