The quickest check is simple: turn on a hot water tap and let it run for 60 to 90 seconds. If hot water arrives within a reasonable time and stays hot, your water heater is doing its basic job. If you get lukewarm water, water that turns cold quickly, no hot water at all, or you notice discoloration or unusual sounds from the unit, those are signals worth investigating. A few additional checks around the water heater itself can help you spot problems before they become emergencies.

Start With the Hot Water Test

Run the hot water at the tap farthest from your water heater — usually a bathroom on the opposite side of the house. If you have a standard tank water heater, hot water should arrive within a minute or two. If it takes significantly longer or never gets fully hot, the heater may be struggling to maintain temperature. At 5,280 feet of elevation, Denver homes already face slightly longer heat-up times due to altitude’s effect on combustion in gas heaters, so some delay is normal — but a dramatic change from your baseline is worth noting.

For tankless water heaters, expect a short wait for the unit to activate and the cold water in the pipes to clear, then a continuous supply of hot water. If a tankless unit delivers hot water briefly and then goes cold, an error code, a flow sensor issue, or scale buildup on the heat exchanger may be the cause.

Visual Checks Around the Unit

Walk over to your water heater and look for these signs:

  • Water on the floor or cabinet base: Any pooling or moisture around the unit is a concern. Small amounts can come from condensation, but active dripping from the tank body, the temperature and pressure (T&P) relief valve, or supply connections indicates a leak that needs attention.
  • Rust-colored water at the drain valve: A small amount of rusty sediment is common in older tanks, but heavy rust can indicate internal corrosion — a sign the tank may be nearing the end of its life.
  • Pilot light status (gas units): If your gas water heater has a visible pilot, check that it’s lit. A pilot that keeps going out often points to a failing thermocouple.
  • Error codes (tankless and newer units): Many modern water heaters display fault codes on a small LED panel. Look up the code in your owner’s manual or take a photo and share it with a technician.
  • Corrosion or mineral buildup on connections: White or greenish crusty buildup around the cold inlet or hot outlet connections, or around the anode rod access point, is a sign of ongoing leakage or mineral activity.

Listen for Unusual Sounds

A well-maintained water heater runs quietly. Popping, rumbling, or banging sounds during heating cycles almost always indicate sediment buildup at the bottom of the tank. In Denver, our hard water leaves calcium and magnesium deposits that accumulate over time, and when the burner fires, water trapped beneath that layer of scale boils and bursts through — producing those sounds. It’s annoying, and it also makes the heater less efficient and shortens its life.

A high-pitched whining or hissing sound can indicate scale on an electric element or a failing heating element in general. A deep rumbling in a gas unit that’s louder than usual can also point to combustion issues — worth having a technician assess rather than ignoring.

Check the Temperature Setting

The U.S. Department of Energy recommends setting your water heater to 120°F for most households — hot enough for comfort and hygiene, low enough to minimize scalding risk and energy waste. If someone adjusted the thermostat dial and it’s set lower, that alone could explain tepid output. On a gas unit, the dial is usually on the gas valve; on electric units, there are typically two thermostats behind access panels on the side of the tank.

When to Call a Professional

If you’ve run through these checks and still can’t identify the problem — or if you find an active leak, a gas smell, or a fault code you can’t resolve — stop troubleshooting and call a plumber. Gas and water together require a licensed professional. Done’s team handles water heater repairs across the Denver metro, and if the unit is beyond repair, we can walk you through replacement options including high-efficiency tank and tankless models. Regular water heater maintenance — including flushing sediment and inspecting the anode rod — is the best way to catch small issues before they become big ones.