When hot water suddenly stops, the culprit is almost always your water heater — but the specific cause depends on whether you have a tank-style or tankless unit, and whether you're getting no hot water at all or just not enough of it. The most common reasons include a failed heating element or burner, a tripped breaker or blown pilot light, a faulty thermostat, sediment buildup that has overwhelmed the heater's capacity, or a unit that has simply reached the end of its service life. Identifying which problem you're dealing with quickly is important, especially in Colorado winters when cold tap water runs very cold and a malfunctioning heater affects everything from morning showers to dishwashing.

Check the Basics First

Before calling a plumber, run through a short checklist. For electric water heaters, check your breaker panel — a tripped breaker is one of the most common reasons an electric heater goes cold without warning. Reset the breaker once; if it trips again, stop and call a pro, because a repeatedly tripping breaker usually signals a deeper electrical or heating-element problem. For gas water heaters, check whether the pilot light is still lit. Most modern gas heaters have an electronic ignition, so a failed igniter is worth checking before assuming the worst. Also verify that your gas supply valve is fully open.

Sediment Buildup Is a Common Culprit in Colorado

Denver and the Front Range have notably hard water — high in dissolved calcium and magnesium. Over time, those minerals settle at the bottom of a tank-style water heater as sediment. A thick layer of sediment forces the burner or heating elements to work harder and longer to heat water through the insulating crust, and it dramatically reduces the effective capacity of your tank. Symptoms include a popping or rumbling sound when the heater is running, lukewarm water instead of fully hot water, and longer recovery times between showers. Annual flushing and descaling can prevent this, but if sediment has built up for years, the heater's inner lining may already be compromised.

Thermostat and Heating Element Failures

Electric tank water heaters use two heating elements — upper and lower — each controlled by its own thermostat. If the lower element fails, you'll get a reduced amount of hot water, not zero. If the upper element or its thermostat fails, you may get no hot water at all. Either scenario requires draining part of the tank and replacing the element, which is a straightforward repair for a licensed plumber but carries real risks if attempted without proper tools — 240-volt circuits and pressurized water are an unforgiving combination. Gas heaters can suffer from a failed thermocouple (the safety sensor that keeps the gas valve open) or a faulty gas valve itself.

No Hot Water From a Tankless Heater

Tankless water heaters have their own failure modes. At Denver's altitude (~5,280 ft), combustion-fed tankless units are factory-set or field-adjusted for thinner air, and an improperly calibrated unit may struggle to ignite reliably or may produce error codes. Common tankless issues include mineral scale on the heat exchanger (hard water strikes again), a dirty inlet filter screen, ignition failure, or a flow sensor that has stopped detecting water movement. Many tankless units display error codes on a small panel — noting the code before you call will help the technician diagnose the problem faster.

When It's Time to Replace, Not Repair

Tank-style water heaters typically last 8–12 years; tankless units often last 15–20 years with good maintenance. If your unit is near or past its expected lifespan, a repair may only buy a few more months before the next failure — and a catastrophic tank failure can mean serious water damage to your home. If your heater is older and exhibiting rust-colored water, visible corrosion, or persistent leaking around the base, replacement is usually the smarter investment.

  • No hot water at all: check breaker (electric) or pilot/igniter (gas) first
  • Lukewarm or limited hot water: likely sediment buildup or a failed lower element
  • Rumbling or popping sounds: mineral scale in the tank — schedule a flush
  • Rust-colored water or visible corrosion: the tank itself may be failing
  • Error codes on a tankless unit: note the code and call for diagnosis

If your hot water isn't working and the simple checks haven't solved it, Done's licensed plumbers can diagnose and repair virtually any water heater make or model — and if replacement is the right call, we'll walk you through your options. Visit our water heater repair page to learn more, or explore all water heater services we offer. For same-day help, contact us anytime — we're here when you need us.