Water heaters rarely fail without warning. In most cases, the unit gives off signals for weeks — sometimes months — before it stops working completely. The problem is that most homeowners don't know what those signals mean until it's too late.
Here are the 10 warning signs San Dimas homeowners should watch for — what each one means, and what to do about it.
In this article
1. Unit is over 10 years old
Age over 10-12 years
Tank water heaters last 8-12 years on average. If yours is over 10 years old, even if it's still "working," it's living on borrowed time. The internal components are wearing out, and failure becomes more likely with each passing month.
2. Rusty or discolored hot water
Brown, orange, or metallic-tasting hot water
Rusty hot water — but clear cold water — points to corrosion inside the tank. The anode rod has typically failed, and the tank itself is starting to rust. Once the tank body corrodes through, repair isn't possible.
Note: If both hot and cold water are rusty, the issue is usually in your home's plumbing — not the water heater. Have a plumber check your pipes.
3. Rumbling, popping, or banging noises
Loud noises during heating
These sounds come from sediment that has hardened at the bottom of the tank. As the burner heats the water, trapped moisture under the sediment turns to steam and "pops." Left untreated, this sediment overheats the tank floor and can crack it.
4. Leaking from the tank
Water pooling under the unit
Any leak from the tank body itself is a serious problem. A leaking tank usually means the steel has cracked or corroded through — and it cannot be repaired. Fittings and valves can leak too, but those are fixable.
Water heater leaking right now?
Our 24/7 connection line is ready. We'll connect you with a local provider who handles leaks fast.
Call (909) 488-72315. Inconsistent water temperature
Shower alternates hot and cold
If your shower temperature swings between hot and cold — a "cold water sandwich" — it usually points to a failing dip tube, thermostat, or mixing valve. In gas units, it can also mean a failing thermocouple.
6. Reduced hot water supply
Hot water runs out faster than usual
If your tank used to give 20-minute showers but now runs out after 5, the heating element or burner may be failing. Sediment buildup is another common cause — the tank can't heat water efficiently through the layer of scale on the bottom.
7. Rotten egg smell
Sulfur or rotten egg smell from hot water
This smell usually means bacteria is growing inside the tank. It's most common when the anode rod has failed and the water chemistry has changed. Replacing the anode rod and flushing the tank typically fixes it.
8. Moisture around the unit
Condensation, puddles, or damp spots
Any moisture around the base of the water heater is worth investigating. It could be condensation (harmless), a small fitting leak (fixable), or the beginning of a tank leak (serious). The only way to know is a physical inspection.
9. Pilot light keeps going out
Pilot won't stay lit (gas units)
If your gas water heater's pilot light goes out repeatedly, the thermocouple or thermopile has likely failed. This is a relatively inexpensive repair ($120-$250) if caught early. Left unaddressed, it can lead to bigger problems or a safety issue.
10. Rising energy bills
Gas or electric bill creeping up
An aging water heater loses efficiency as sediment builds up inside the tank. The unit has to work harder to heat the same amount of water. If your utility bill has climbed 10-20% without explanation, the water heater may be the cause.
When to call a professional (vs when to wait)
Not every warning sign is urgent. Here's how to prioritize:
Call immediately (emergency): Burst tank, active flooding, gas smell, sparks from the unit, no hot water in winter with kids/elderly in the home.
Call within 24-48 hours: Leaking from the tank body, rusty hot water, loud popping or banging noises, pilot light won't stay lit.
Can wait for a scheduled visit: Slightly reduced hot water, mild temperature fluctuations, unit over 10 years old (planning mode), rising energy bills.
Frequently asked questions
How long do water heaters last in San Dimas?
Tank units last 8-12 years on average. Tankless units last 20+ years with annual descaling. San Dimas water is moderately hard, which shortens tank unit lifespan without regular maintenance.
What is the first sign a water heater is failing?
Usually inconsistent hot water or rumbling noises from sediment buildup. Both are early warning signs that can often be addressed with maintenance before full failure.
Can a failing water heater be repaired?
Some failures are repairable — thermocouple, heating element, thermostat, dip tube, anode rod. Others (like a leaking tank or corroded body) require replacement. A licensed provider diagnoses the specific issue.
When should I replace my water heater instead of repairing it?
If the unit is over 10-12 years old, the tank is leaking, the body is corroded, or the repair costs more than 50% of a new unit, replacement usually makes more sense.
What should I do first if I notice a warning sign?
Turn off the water supply and power to the unit (breaker for electric, gas valve for gas). Then call for service. Don't try to diagnose or repair it yourself — especially for gas or electrical issues.