Four symptoms, not one problem
No hot water at all. Every hot tap in the house runs cold and stays cold, however long you leave it. The heater is not making heat. On a gas unit that usually means the burner is not firing. On an electric unit it usually means no power reaching it, or the upper element is dead.
Lukewarm water that never gets hot. Something is heating, just not enough. On an electric heater that is most often one of the two elements gone, or a thermostat set low or failing. On a gas heater it can be the thermostat on the gas control, or a burner firing weakly through a layer of sediment.
Hot water that runs out in minutes. The heater makes hot water and then stops having any. That is a volume problem, not a heat problem — a dead lower element, a broken dip tube, or enough sediment in the bottom of the tank that the usable capacity is a fraction of what is on the label. A tank that then takes hours to come back is telling you the same thing.
Hot water everywhere except one fixture. If the rest of the house is fine, the heater is fine. The fault is at that fixture — a failed mixing cartridge in the valve, a scaled-up aerator, a closed or partly closed angle stop, or a tempering valve. Nobody needs to touch the tank for this one.
Sort out which of the four you have first. It is the difference between a part on the wall, a part in the tank, and a tank that is finished.
"No hot water" and "hot water that runs out in ten minutes" are not the same complaint. One is a heat problem and the other is a volume problem, and they point at different parts.
Gas and electric fail in different places
A gas heater makes heat with a burner under the tank. The usual reasons it stops are the pilot or ignition and the gas control. On an older standing-pilot unit, the pilot goes out and a thermocouple — a small probe sitting in the pilot flame — stops sending the signal that keeps the gas valve open. That is the single most common no-hot-water call on a gas tank, and the thermocouple is a part. On a newer unit with electronic ignition there is an igniter, a sensor and a control board doing the same job. A gas control valve can also fail outright, and a blocked flue or a closed supply valve will stop the burner for reasons that have nothing to do with the heater itself.
A pilot that lights and then drops out after a few seconds is pointing at the thermocouple. A pilot that will not light at all is pointing further upstream, at gas supply or the control.
An electric heater makes heat with elements screwed through the tank wall into the water. Most residential tanks have two, one high and one low, and they do not fire at the same time. The upper one heats the top of the tank first, then hands over to the lower one. That wiring is why the symptoms split so cleanly: a dead upper element gives you no hot water at all, and a dead lower element gives you a small amount of hot water that runs out fast and then takes a long time to return.
Above both elements sits a high-limit cutoff — a red reset button behind the upper access panel. When water in the tank gets too hot, it trips and kills power to both elements, and the result at the tap is no hot water from a heater that looks perfectly normal. A cutoff that has tripped once may just have tripped. A cutoff that trips again after a reset is reporting a fault, usually a stuck thermostat or a shorted element, and it should not be reset a third time and left.
And an electric heater draws enough current that a tripped double-pole breaker is a real and common answer. Check that before anything else.
What a homeowner can check safely
The breaker. On an electric heater, find the double-pole breaker in the panel and look at it. If it has tripped, reset it once. If it trips again, stop — a breaker tripping on a water heater is a fault being reported, not a nuisance, and it needs the circuit and the elements looked at.
The gas supply valve. Follow the gas line to the heater and confirm the handle is in line with the pipe, not across it. Valves get knocked closed during other work more often than you would expect.
The pilot, if the unit has a visible one and the manufacturer's instructions are still on the jacket. Follow those instructions exactly, and only those. If it will not light, or lights and drops out, that is the answer — leave it and call. Do not keep cycling the gas control trying to make it hold.
The thermostat setting. On a gas unit it is the dial on the control at the bottom. On an electric unit it is behind the access panels, and reading the number is one thing but adjusting it means pulling a cover off a live 240-volt circuit — that one is not a homeowner job unless you can kill the breaker and confirm it is dead. A setting somebody moved, or a tank that was switched to vacation mode and never switched back, explains more lukewarm-water calls than any failed part.
The single fixture. If only one tap is cold, take the aerator off and look at it, and check the angle stops under the sink are fully open. A shower that has gone lukewarm when the rest of the house is hot is usually a mixing cartridge in the valve body, and that is a fixture repair.
Whether the household simply used it. A tank heater has a finite amount of hot water and a recovery time. Three showers back to back on a small tank will empty it, and that is not a fault. The question is whether it ran out sooner than it used to.
What needs a plumber, and why
Anything inside the gas control. Thermocouples, igniters, sensors and gas valves are serviceable parts, but they sit on a gas appliance in a closed space, and a unit that is relit without finding out why it went out is a unit that goes out again. Gas work also gets done under a licence for a reason.
Anything behind the electrical panels on the heater. Elements and thermostats are cheap parts and routine replacements, and they are also wired to 240 volts inside a cabinet strapped to a tank full of water. Testing an element for continuity, confirming which of the two has failed, and pulling one out of a tank wall without damaging the threads are all straightforward with the right tools and unpleasant without them.
A high-limit cutoff that keeps tripping. The reset button is the symptom. The thermostat or element behind it is the fault.
Slow recovery and reduced capacity. If the heater makes hot water but far less of it than it did, somebody has to drain and flush it and see what comes out, then test the lower element. Most of Pasco County runs hard water, and in a tank the dissolved calcium and magnesium settle on the bottom as sediment every time the water is heated. That layer buries the lower element so it fires inside a crust instead of in water, insulates the bottom of a gas tank from the burner, and takes up volume the tank was supposed to be storing. Rumbling or popping when the heater runs is water boiling in pockets under it.
An element that burns out, gets replaced, and burns out again. The part is not the problem. The sediment it is sitting in is.
We do not name a number before looking at the heater, and we will not guess what is wrong with yours over the phone. Pipe Perfect LLC is a Florida Certified Plumbing Contractor, licence CFC1431903, and the work is permitted and inspected under that licence.
When it is the tank and not a part
Most no-hot-water calls are a part. These are the ones that are not.
Water appearing from under the jacket with every visible fitting dry. Dry the area, lay paper towel down, and look again in a few hours. Water pools at the base of a heater whatever leaked, so the base tells you there is a leak and not what failed. If the inlet and outlet fittings, the relief valve, the drain valve and the pan fitting are all dry and water is still arriving, it is the tank.
Rust weeping or streaking down the shell from a welded seam. Staining in the pan that comes back after you dry it.
Rusty or brown water on the hot side only, with the cold side running clear. That is the inside of the tank arriving at your tap, and it means the glass lining has gone.
A tank is a welded steel vessel with a thin lining fired onto the inside. Once the lining fails, heated water corrodes bare steel from the inside out. By the time water shows on the outside, the metal around that spot has been thinning for years and there is nothing sound to patch to. There is no repair for that, and no element, thermostat or thermocouple changes it.
Age belongs in this list too. A standard tank heater runs roughly eight to twelve years and a tankless unit commonly fifteen to twenty — those are general service-life ranges for the appliance, not a reading on yours, and we would need to see it and the data plate to say anything about the one in your garage. A heater at the far end of that range that has now had its third part fail is telling you something the individual parts do not.
If the tank is going, where it sits matters while you decide. A heater on a garage slab that drains is a different risk from one in an interior closet over finished floor. Whether any resulting water damage is covered is between you and your carrier — policies commonly treat the failed appliance and the damage it caused as two separate things, and we do not know what yours says. Photograph everything, dated, before anyone starts pulling up flooring.