No hot water from a gas tank
A safe order for a gas storage heater that produces nothing: fuel, control setting, ignition, flammable-vapor lockout, and when to stop resetting.
“No hot water” from a gas storage tank means the burner is not heating the water, or the hot water is not leaving the tank. It does not mean the tank is too small.
A tank that is hot for a few minutes and then fades is a different page, hot water that runs out. This page is the heater that never gets there.
If you smell gas, stop reading and leave the house. Call the gas utility from outside. Do not click an igniter, do not flip a light switch, and do not decide it is “just the pilot.”
The machine you are looking at is either a standing-pilot atmospheric tank, an electronic-ignition atmospheric tank, or a fan-assisted or condensing tank. The outside of the jacket will not always tell you.
The manual and the viewing window will. Anatomy is in how a storage tank works. Condensing lockouts that involve the vent or the condensate trap are in condensing gas heaters and in venting.
Confirm the complaint before you touch the gas control
Open a hot faucet at the nearest tap and let it run. If the water is cold at every tap and stays cold, you are on this page. If one faucet is cold and another is hot, the heater is probably fine and that faucet’s cartridge or shutoff is not.
If the water is warm but not hot, measure it. A thermostat turned down, a mixing valve set low, or a broken dip tube can all feel like “no hot water” to someone who expected 120°F and got 90°F. A thermometer is cheaper than a gas valve.
Look at the cold-water shutoff on top of the heater. A valve closed after a repair leaves the tank full of water that never gets replaced, and the outlets can go odd in a way that mimics a dead heater.
Confirm it is open. Confirm the gas shutoff in the pipe ahead of the heater is parallel to the pipe, which is the usual open position, and that any other gas appliance in the house lights.
If the range will not light either, the problem is the gas service, not the water heater. Call the utility. If the range lights and the heater does not, the supply to the house is present and the heater or its connector is the suspect.
The setting on the control
Standing-pilot controls have a knob with positions that include off, pilot, and on. If someone turned it to pilot, the main burner will not fire and the tank will slowly go cold. If they turned it to off, even the pilot is out.
Follow the lighting instructions printed on the heater, once. Hold the knob the way the sticker says, light the pilot the way the sticker says, and release only when the sticker says the thermocouple should hold.
If the pilot lights and dies when you release the knob, you are done with homeowner lighting. That failure is a pilot that will not stay lit.
Do not improvise a sequence from memory. Do not retry ten times. Unburned gas in the combustion chamber is how lighting attempts become fires. If the sticker says wait five minutes between attempts, wait.
Electronic controls often have a power switch and a status light, sometimes behind a small door.
A heater that was working yesterday and is dark today may have a tripped breaker or a GFCI receptacle that protects the control.
Look at the breaker handle once. If it is off, switch it on and watch. If it trips again, leave it off.
That is an electrical fault, and the next page is electrical safety, not another reset. Many gas valves also have a high-limit or a flammable-vapor lockout that will not reset until the underlying condition is gone.
Flammable vapor lockout
Gas water heaters sold in the United States for many years have been flammable-vapor-ignition-resistant. A flame-arrestor screen admits air and is designed so vapors from a spilled solvent or gasoline do not ignite in the room. If the screen is blocked with lint, or if the sensor decides vapors are present, the control locks out and you get no hot water. That is the device working.
Do not bypass the sensor. Do not punch holes in the screen. Move gasoline, paints, and rags out of the room, ventilate, and read the reset procedure in the manual for that model.
Some resets are a switch sequence. Some require a part.
If lint is packed on the screen, cleaning may be described in the manual and may require removing the burner assembly, which is not a casual job: you are opening the gas path. A homeowner who has not done that job on this model should stop.
A technician can measure draft, clean the arrestor without damaging it, and confirm the gas valve still proves flame. Storing the water heater inside a paint locker is not a layout you put back when you are done.
What the status light is saying
Brands use flashes or numeric codes, and they reuse them on different generations. Count the flashes, write the number down, and match it to the sticker inside the access door or the manual for that serial number.
Do not use a chart you found for a different brand. In plain language, the families of faults on a tank that will not heat are: no proof of flame, a pressure switch or inducer fault on fan-assisted models, a high-limit trip, a flammable-vapor trip, and a failed gas valve.
The first of those can be a dirty flame sensor, a weak igniter, a closed gas cock you missed, or inadequate gas pressure under fire. Pressure is measured with a manometer. The rating plate states the manifold pressure. Adjusting the valve to “make it stronger” is not a homeowner repair and it is a good way to produce carbon monoxide.
If the burner lights, runs briefly, and shuts off, look up at the draft hood only if you can do it without removing vent pipe. Soot, melted plastic grommets, or a flame that rolls out of the bottom are signs the flue is not drafting. Stop using the heater. That is the venting guide, and it is a service call, not a longer shower.
What you can check and then stop
Checklist: one pass, then a person with a meter
- Smell. Any gas odor ends the project. Leave and call the utility.
- Other gas appliances. If they are also dead, call the utility before you touch the heater.
- Cold-water valve open, gas cock open, control not sitting on “pilot” or “vacation.”
- Breaker or receptacle for an electronic control, reset once only.
- Lighting sequence on the sticker, one attempt, then the pilot article if it will not hold.
- Status light or code written down, matched to this model’s manual.
- Lint and stored chemicals removed from the burner area. No holes in the screen.
- If the burner lights and the flue looks distressed, shut the heater off and call.
A failed thermocouple, a failed flame sensor, a failed igniter, and a failed gas valve all present as “no hot water.” The part is not identifiable from the kitchen. Replacing a gas valve means breaking a gas connection, setting pressure, and checking for leaks with the method the code requires, not with a lighter.
That is licensed work in many states even when a homeowner exemption exists for other chores, and it is unsafe work everywhere if you are guessing. When to call a pro puts gas-valve and burner work on the licensed side of the table on purpose.
If the tank is over about ten years old and the quote for a gas valve approaches the quote for a new heater, read repair or replace before you approve the part. A new valve on a tank that is about to leak at the bottom is a short victory. A new valve on a six-year-old tank with a sound flue is often the right spend. Get both prices.
Sources
U.S. Department of Energy, Energy Saver, “Which Water Heater Is Right for You?” Manufacturer lighting instructions on the heater’s data-plate area and in the installation manual (Bradford White, bradfordwhite.com; A. O. Smith, hotwater.com; Rheem, rheem.com). ANSI Z21.10.1 flammable-vapor requirements are why the screen and the lockout exist; the model’s manual is the reset procedure. U.S. Consumer Product Safety Commission carbon monoxide guidance, referenced from the venting guide.