Water heater: repair it or replace it? (the 10-minute decision)

A water heater is one of the few appliances where "just replace it" is often the cheaper answer. Here's how to tell in ten minutes, before you spend $250 on a service call.

Step 1: How old is it?

Find the serial number on the manufacturer label. The first two digits (or the letter-plus-number) encode the year — most brands put a decoder on their website. Rule of thumb:

• Under 6 years: repair almost always wins.
• 6–10 years: repair if it's cheap (thermostat, element, pilot). Replace if it's the tank itself.
• Over 10 years (tank) / 15 years (tankless): replace. You're on borrowed time and the next failure is a flooded floor.

Step 2: Match the symptom

| Symptom | Likely cause | DIY cost | Verdict | |---|---|---|---| | No hot water (gas) | Pilot out, thermocouple | $0–$25 | Repair | | No hot water (electric) | Tripped breaker, dead element or thermostat | $20–$60 | Repair | | Not enough hot water | Sediment, bad lower element, dip tube | $0–$40 | Repair if under 10 yrs | | Rusty or brown hot water | Anode rod spent, tank rusting inside | $30 (anode) | Repair once; if it returns, replace | | Popping / rumbling | Sediment on the bottom | $0 (flush) | Repair | | Water around the base | Tank leak, T&P valve, fitting | $0–$30 if a fitting | Replace if the tank itself is leaking | | Rotten-egg smell | Bacteria + magnesium anode | $40 (aluminum/zinc anode) | Repair |

A tank that is leaking from the tank body is not repairable. Everything else on this list is a 30- to 90-minute job with hand tools.

The three fixes worth knowing

Relight the pilot / replace the thermocouple (gas). Instructions are printed on the tank. If the pilot won't stay lit, the thermocouple is a $15 part and a 20-minute swap.

Flush the tank. Shut off power or gas, connect a hose to the drain valve, run it to a floor drain, open the T&P valve to let air in, and drain until the water runs clear. Do this once a year and most heaters last well past 12 years.

Replace the anode rod. This is the sacrificial metal rod that rusts so your tank doesn't. If it's down to bare wire, the tank starts rusting next. A new rod is $30 and a 1-1/16" socket with a breaker bar. Many tanks have never had this done — it's the single best maintenance task nobody does.

When replacement is the smart money

A new 40- or 50-gallon tank runs $500–$1,200 installed yourself, $1,200–$2,500 installed by a plumber. Replace rather than repair when:

• The tank is over 10 years old and you're facing any repair over $200.
• There's water coming from the tank body (not a fitting).
• You've flushed it, replaced the anode, and the rusty water came back within a few months.
• Your energy bills have crept up and the unit is pre-2015 (efficiency standards changed).

Consider a heat-pump water heater if you have the headroom and a warm-ish utility space — they cost more up front but typically cut water-heating energy use by 60% or more, and federal/utility rebates often cover a large chunk of the premium.

What I'd hire out

Gas-line work, venting changes, and any replacement where the new unit is a different fuel type or size class. A wrong vent on a gas heater is a carbon-monoxide problem, not a plumbing problem. Everything in the "three fixes" section is fair game for a careful homeowner.