No Hot Water: What to Check

By the San Antonio 24 Hour Plumber team · Updated September 2026

Start With the Symptom, Not the Appliance

"No hot water" covers several different faults, and describing yours precisely saves a lot of time. There is no hot water at all, anywhere. There is hot water but it runs out far sooner than it used to. The water is warm rather than hot. Or one particular tap or shower is cold while the rest of the house is fine. Those four point in genuinely different directions, and the last one usually is not the heater at all — it is a mixing valve or cartridge at that fixture.

Safe Checks on an Electric Heater

If the unit is electric, the first thing to look at is the breaker panel. A tripped double-pole breaker for the water heater is a common and completely ordinary cause, and resetting it once is reasonable. If it trips again straight away, stop — that is the heater telling you something is wrong with an element or the wiring, and repeatedly resetting it is not a fix.

Most electric heaters also have a high-limit reset button behind a small access panel, usually red. Pressing it once is within the range of things a homeowner can reasonably do, provided the power is off at the breaker first and the area around the unit is dry. If it needs resetting again a day later, the thermostat or an element is failing.

Beyond that, leave it. Do not remove element covers, test wiring or open thermostats with the power on.

Safe Checks on a Gas Heater

With gas, the safety rule comes before everything else: if you can smell gas, do not touch anything, leave the building and call the gas utility from outside. Do not flick switches on your way out.

If there is no smell of gas, you can look at whether the pilot is lit on an older unit, or whether the status light is signaling a fault on a newer one. Relighting a pilot is acceptable if you follow the instructions printed on the heater's own label exactly, step by step. If it does not light on the second attempt, stop. A pilot that will not stay lit is usually a thermocouple or a gas valve problem, and both are jobs for a plumber. Never work on a gas heater standing in water, and never touch the burner assembly, the gas control valve or the flue.

What the Noises and the Water Tell You

A tank that rumbles, pops or bangs while heating is almost always full of sediment. So is one that produces hot water for a much shorter time than it used to. Rusty or cloudy hot water points at the inside of the tank or a spent anode rod. A dripping temperature and pressure relief valve is a warning about pressure or temperature in the system and should never be plugged or ignored. Water pooling at the base of the unit needs the source identified: a fitting or valve above the tank is a repair, but water coming through the tank body means the shell has corroded through and the heater needs replacing.

On a tankless unit, the classic symptom is water that goes hot, then cold, then hot again mid-shower. That is usually scale on the heat exchanger, a fouled flow sensor or insufficient gas supply — all serviceable, none of them a reason to replace the unit on the spot.

Why This Happens So Often in San Antonio

Hard water is the reason. Edwards Aquifer water carries a heavy mineral load, and every time a tank heats it, some of that mineral drops out and settles on the bottom. Over years that layer grows into an insulating blanket between the burner and the water, so the unit works harder, takes longer, holds less usable hot water and makes the rumbling noise people describe. In a tankless heater the same mineral coats the heat exchanger instead.

This is why flushing is not optional here in the way it might be somewhere with soft water, and it is also why a heater can seem fine one winter and struggle the next. In Boerne and the surrounding Kendall County properties the effect is stronger again, because many homes draw from private wells and rely on a softener that may itself have quietly stopped regenerating.

Arrange an Inspection

If the safe checks have not restored hot water, the next step is testing rather than replacing. San Antonio 24 Hour Plumber tests thermostats, elements, gas controls, thermocouples and dip tubes, flushes tanks and descales tankless units — details are on the water heater repair page. If someone has already told you the unit needs replacing, read the repair versus replacement comparison first, because the answer usually comes down to whether the tank itself is leaking. If there is water on the floor and you are not sure it is from the heater, start with leak detection, or describe what you are seeing and we will work out which visit you need.