A routine maintenance visit turned into an expensive surprise for one homeowner after a long-neglected tankless water heater developed a leak almost immediately after being flushed.

Upgrading to a heat pump water heater can turn an emergency purchase into an opportunity to lower monthly utility bills.

Here's what to know

The heater itself was not the initial focus of the visit. In a Reddit post on r/Plumbing, the original poster said they had a pressure-reducing valve replaced because of a leak, hammer noise, and fluctuating pressure. During that same appointment, they also agreed to a flush for their 15-year-old Rheem tankless unit, which had been trouble-free despite the home's hard-water conditions.

Initially, nothing seemed wrong. The issue only became apparent after a shower, when the homeowner said they found "a small puddle under the tankless heater." After removing the cover, they discovered what looked like "one of the copper pipes by the heat exchange has a pinch hole."

Hard-water scale can build up inside older units over many years. In some cases, that mineral buildup may do more than reduce efficiency — it may also be masking weak spots that have formed in aging metal.

One commenter suggested it was time to move on, writing, "Definitely time to replace and the average lifespan is around 10-12 years now, and that's if you're lucky."

More background

Flushing a tankless water heater is typically recommended, especially in hard-water areas, because scale can drag down performance and force the unit to work harder. But when a heater has gone 15 years without that service, the first descale can expose corrosion that had effectively been sealed over.

The flush may not have caused the damage so much as revealed how worn the heat exchanger area already was. The water heater may already have been at or beyond the point where replacement was the more realistic outcome. What starts as a relatively modest maintenance add-on can quickly turn into a full appliance replacement.

What can be done?

In hard-water areas, keeping up with descaling before a system reaches old age can help preserve efficiency, extend equipment life, and reduce the chances of discovering that mineral buildup was the only thing preventing a weak spot from leaking.

If your unit is already old, it may be worth asking a licensed plumber for an honest assessment before scheduling major maintenance. In some cases, budgeting for a replacement may make more sense than putting more money into a heater that is already nearing the end of its expected lifespan.

Another option is Cala. The company's customizable smart heat pump water heaters help homeowners decrease their energy bills by heating water exactly when it's needed. That can help households avoid wasting electricity and potentially save hundreds of dollars a year compared with less efficient setups. For people who have to replace an aging water heater anyway, Cala offers a way to make that upgrade work harder for their budget over time.

The original poster wrote: "Lesson learned — don't flush a tankless heater that hasn't been serviced in 15 years."

Where can I learn more?

Leaks, corrosion, and overdue maintenance usually don't get much attention until a water heater starts acting up. Here are a few useful reads on maintenance basics, corrosion red flags, replacement choices, tankless quirks, and the tradeoffs of switching systems.

• A home expert says critical tips to keep a water heater efficient can save money.

• Reddit users warned whole-house softeners can kill tanks after an anode disintegrated and smells spread.

• One homeowner with a corroded gas unit weighed replacement options for homeowners as tankless looked tempting.

• A tankless setup delivered endless hot water until showers went weak when nearby toilets flushed.

• Homeowners weighing an upgrade still debate the pros and cons of going tankless before committing.

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