10 Signs Your Water Heater Is About to Fail (And What to Do)
A water heater that fails catastrophically can dump 40 to 80 gallons of water across a basement floor in minutes. The good news: water heaters almost always give warning signs weeks or months before they actually fail. Catching the signs early lets you schedule a planned replacement instead of dealing with an emergency, water damage, and a forced decision under pressure.
Here are the ten signs we see most often in southern New Hampshire homes, and what to do about each.
1. The tank is past 10 years old
Age is the single most important warning sign. Most tank-style water heaters in NH homes have an expected lifespan of 8 to 12 years. Past 10 years, the tank is on borrowed time even if it is still working. Past 12 years, replacement should be on the calendar.
How to check the age: the data plate on the side of the tank lists the manufacture date. For some brands, the date is encoded in the serial number (first four digits are typically year and month).
2. Rusty or discolored hot water
If your hot water is reddish-brown or has visible particles, the steel tank is corroding from the inside. The glass lining has likely cracked and exposed the steel underneath. This means tank failure is approaching.
How to verify it is the water heater, not the supply: compare hot and cold water at the same fixture. If only the hot water is discolored, the source is the water heater.
3. Popping, rumbling, or banging noises during heating cycles
Sediment built up at the bottom of the tank traps water that superheats and produces popping or rumbling sounds when it escapes. The sediment also insulates the burner from the water (on gas units), which overheats the bottom of the tank and accelerates failure.
What to do: have the tank flushed by a licensed plumber. If noises persist after flushing, the sediment may be permanently fused to the tank bottom, signaling end of life.
4. Visible moisture, rust, or scale around the base
Any moisture at the base of the water heater is a warning sign. It could be:
- A small leak from a fitting (sometimes fixable)
- Condensation from temperature differential (usually harmless)
- A slow leak from the tank itself (replacement needed)
A licensed plumber can identify the source. A leak from the tank itself is not repairable.
5. Frequent or growing repair needs
If you have replaced multiple components in the past year or two (thermostat, heating element on electric units, gas valve on gas units), the unit is signaling it has more failures coming. The general rule: if upcoming repairs would cost more than 50 percent of a new unit, replacement is the better value.
6. Inconsistent water temperature
Hot water that fluctuates between hot and lukewarm during a single shower indicates failing controls or a degraded heating element. Could be a thermostat issue (sometimes repairable) or the start of larger system failure.
7. Reduced hot water capacity or longer recovery time
If showers run out of hot water faster than they used to, or the tank takes longer to recover between uses, the heat-transfer capacity is degrading. On gas units, this is often sediment buildup. On electric units, it can be a failed lower heating element.
8. Rising energy bills with no change in use
A water heater operating at degraded efficiency uses more fuel or electricity to maintain the same setpoint. Often the result of sediment buildup, failing insulation, or a partially failed heating element.
9. Rotten egg smell from the hot water
This is usually a chemical reaction between the anode rod (typically magnesium) and sulfur bacteria in the water supply, especially on well water. Not necessarily a sign the tank itself is failing, but a sign the anode rod needs attention.
What to do: replace the magnesium anode rod with an aluminum-zinc or powered anode rod. If the rod has not been checked or replaced in 5+ years, this is overdue regardless of the smell.
10. Low water pressure on the hot side only
If hot water trickles while cold water flows normally at the same fixture, the issue is in the water heater or its piping. Possible causes:
- Sediment partially blocking the tank outlet
- Mineral buildup in the hot-water supply pipe from the tank
- Failing dip tube inside the tank
Sometimes repairable; sometimes a sign that the tank itself is near end of life.
What to do if you see warning signs
Schedule a professional assessment
A licensed plumber can determine which signs indicate fixable component failures and which indicate end of life. Catching the issue early means a scheduled replacement on your timeline rather than an emergency.
Plan for replacement before failure
A planned replacement gives you time to compare options:
- Modern tank water heater (familiar, lowest install cost)
- Heat pump water heater (highest efficiency; the federal 25C tax credit ended December 31, 2025, but NHSaves rebates may apply)
- Tankless on-demand (longest lifespan, unlimited hot water, higher upfront cost)
- Indirect water heater (if you have a boiler that can support it)
Consider a whole-home leak detection system
A Moen Flo or similar smart shut-off system installed at the main water line provides continuous monitoring and can automatically shut off the main water supply if a leak is detected. The first averted flood pays for the system many times over.
Schedule a water heater assessment
If your water heater is past 10 years old or showing any of the warning signs above, contact A.J. LeBlanc Heating. Serving New Hampshire families since 1928.
Frequently Asked Questions
How long does a water heater last in NH?
A standard storage tank typically lasts 8 to 12 years. With consistent maintenance (anode rod replacement, annual flushing), up to 15 years. Tankless and heat pump water heaters typically last 15 to 20 years.
Is rusty hot water dangerous?
Not immediately dangerous to drink, but it indicates the steel tank is corroding. Replacement is approaching.
Can I extend my water heater's life?
Yes, substantially. Annual flushing, anode rod replacement every 3 to 5 years, and T&P valve testing can roughly double the useful life of a tank-style water heater.
Should I repair or replace?
If the tank itself is leaking, replace. If the repair cost exceeds 50 percent of a new unit, replace. If the unit is past 10 years old with multiple recent repairs, replace. Otherwise, repair may be the better answer.
What happens if my water heater fails catastrophically?
The tank can dump 40 to 80 gallons of water across the floor and continue flowing as long as the main supply is on. Knowing where your main water shut-off is, and ideally having a Moen Flo or similar smart shut-off system, dramatically reduces the damage if this happens.