Which faults are repairable
Most single faults are repairable when parts exist: a failed thermocouple or thermopile on a gas tank, a tripped high-limit, a failed electric element or thermostat, a fouled flame rod or blocked condensate trap on a tankless unit, a weeping relief valve or a failed dip tube. Bradford White's service manual treats these as field-replaceable items with defined tests, and CANRO's diagnostic visit tests before it replaces parts: gas pressure, ignition and flame signal, sensor resistance and outlet temperature.
Two faults are never repairs. A leaking tank body means the glass lining and steel have failed, and no sealant or patch is a lasting fix. A heat exchanger damaged by scale on a tankless unit is usually beyond economical repair once it is out of warranty, which is why manufacturers make flushing a warranty condition.
The age and history test
Age is a frame, not a verdict. Storage tanks commonly last 8 to 12 years with anode maintenance, and most carry 6 or 10-year tank warranties without labour; a 14-year-old tank with a failed control is a poor repair bet because the tank itself is near or past its useful life. A 4-year-old tank with a failed thermostat is an obvious repair. Between those, the history decides: one clean fault on a maintained unit favours repair; repeated faults, corrosion symptoms or a unit that has needed annual attention favour replacement.
Parts availability is the second test. Bradford White and Rinnai support current models for years, but discontinued controls and boards eventually run out, and the warranty route for a current model may be faster than a repair on an orphaned one.
What the diagnostic visit settles
CANRO publishes that repair visits carry a diagnostic service fee credited toward the repair if you proceed, and that replacement and installation estimates are free. The visit produces a written explanation of the fault, a price for the repair, and an honest recommendation when replacement makes more sense: the free written estimate for the replacement is part of the same conversation, so you are never choosing between a quoted repair and an unknown replacement cost.
A leak is handled differently: shut off the cold-water supply and turn the gas control to OFF or the breaker off if safe, then call. The visit confirms the leak source, and a leaking tank goes straight to a replacement estimate.
When the replacement is an upgrade decision
If the answer is replacement, the same visit answers the upgrade questions: stay with the same tank type under the existing flue, move to a power-vent or condensing unit, or convert to tankless. Each path changes venting, gas supply, condensate and electrical work, and the estimator on this site itemizes those as separate adders so the like-for-like cost and the conversion cost are both visible before you commit.