No Hot Water? What to Check First

By the San Marcos Emergency Plumber team · Updated September 2026

Work Out What Kind of Heater You Have

Before anything else, establish two things: tank or tankless, and gas or electric. A traditional tank sits in a closet, a garage or an attic and holds its hot water. A tankless unit is a wall-mounted box, usually in a garage or on an exterior wall, that heats on demand. An electric heater has a cable running into it and no flue; a gas heater has a gas line and a vent pipe. Those two facts decide every check that follows, and they are the first things a technician will ask you on the phone.

Safe Checks on an Electric Heater

Start at the breaker panel. A double-pole breaker labelled for the water heater that has tripped is a common and simple cause, and resetting it once is reasonable. If it trips again straight away, stop — something is drawing a fault and repeatedly resetting it is not a fix. Many electric tanks also have a reset button behind an access panel; pressing it once is within reach of most homeowners, but do not remove the panel while the power is on and do not touch the wiring or the elements behind it.

Check the thermostat setting if it is accessible from outside the unit. Someone may have turned it down, or a holiday setting may still be active from a trip.

Safe Checks on a Gas Heater

The only rule that matters first: if you smell gas anywhere near the unit, do not touch anything. Leave the building, take everyone with you and call from outside. Do not flip switches, do not light anything and do not go back in to check.

If there is no gas smell, look at the control valve on the front of the tank. Confirm the dial is on and not set to pilot or vacation. Many newer units have a small status light that blinks a fault code, and the legend for those codes is printed on the same label. Reading that light and writing down the pattern is genuinely useful information for the technician. Relighting a pilot is only reasonable if the printed instructions on the unit tell you how and there is no gas odour. Beyond that, gas appliances are not a place to experiment.

Safe Checks on a Tankless Unit

Tankless heaters usually display an error code on a small panel or a remote controller. Note the code and look for the legend in the manual or on the inside of the cover. Check that the unit has power and that its gas supply valve is open. Check the inlet filter screen if the manufacturer's instructions describe how, because a blocked screen restricts flow and can stop the unit firing. Do not open the sealed combustion chamber and do not attempt a descale with the unit live.

The Hard Water Problem in This Area

San Marcos and the towns around it run on Edwards Aquifer water, which carries a lot of dissolved mineral. In a tank, that mineral settles to the bottom as sediment; water trapped under the sediment boils and gives you the familiar rumbling or popping noise, the unit works harder, and the hot water runs out sooner than it used to. In a tankless unit, the same mineral forms scale on the heat exchanger and gradually strangles the flow until the unit throws a code mid-shower.

Neither of those is a broken heater. Both are service items, and both respond to flushing or descaling. It is the single biggest difference between a heater that reaches its expected life here and one that does not. Newer homes in Buda often have tankless units that have never been descaled, and the symptoms arrive right on schedule.

Arrange an Inspection

If the simple checks do not restore hot water, the next step is a proper diagnosis rather than replacing parts by guesswork. San Marcos Emergency Plumber handles water heater repair on tank and tankless units and tests the fault before quoting. If the unit is old or the tank is weeping, read repair versus replacement so you know which questions to ask. Where there is water on the floor as well, leak detection establishes whether it is the heater or a supply line. Request a visit and have the model label to hand.