Gas Water Heater Burner On but No Hot Water
On this page (6 sections)
The Short Answer: If the main burner is really firing, the heater is making heat. The problem is that hot water isn’t reaching your taps, or heat isn’t reaching the water. The usual causes are a broken dip tube, a failed mixing valve, a hot-side valve left partly closed, a faucet letting cold water cross into the hot line, or a heavy layer of sediment. None of these is an ignition problem.
First, make sure it’s the main burner
The small pilot flame stays lit all the time on many tanks. The main burner is the large ring of flame that comes on when the tank calls for heat, usually with a soft whoosh. If only the pilot is lit and the main burner never comes on, see pilot light lit but burners won’t ignite instead.
Narrowing it down
| Clue | Likely cause |
|---|---|
| Very short burst of hot water, then lukewarm; white plastic bits in faucet screens | Broken or missing dip tube, so cold water enters at the top of the tank |
| Pipe leaving the top of the tank is hot, but every tap is lukewarm | Mixing valve on the hot outlet stuck or set low |
| Pipe leaving the tank is hot, one fixture is cold or lukewarm | That fixture’s cartridge or valve |
| Hot water pressure much weaker than cold, right after a replacement | Hot-side shutoff not fully open, or a kinked connector |
| Rumbling or popping, very slow recovery, older tank | Thick sediment insulating the bottom of the tank |
| Hot water gets weaker when someone uses cold elsewhere | Crossover through a single-handle faucet or a recirculating pump setup |
What you can check safely
- The valves at the heater. The cold inlet and, if there is one, the hot outlet valve should both be fully open. Ball-valve handles should be parallel to the pipe. A valve left half-closed after a replacement is common; see low water pressure after installing a water heater.
- Is there a mixing valve? It’s a brass valve with three connections on or near the hot outlet, often with a dial. If yours has an adjustment knob, the manual for that valve shows the setting range. If you are not sure, leave it for the plumber.
- Which fixtures are affected. If one faucet is cold and the rest are fine, the heater isn’t the problem.
- Faucet aerators and shower heads. Bits of white plastic in them point to a disintegrating dip tube.
- The temperature dial. Leave it at the normal setting. Turning it up hides a mixing or dip-tube problem and raises the scald risk.
What the technician will check
A plumber typically compares the water temperature at the tank outlet with the temperature after any mixing valve and at the taps. That shows whether the heat is lost inside the tank or in the plumbing. To check the dip tube, they shut off the water and energy, relieve pressure, and remove the cold inlet fitting. For sediment, they drain and flush the tank and judge from what comes out whether flushing is worthwhile. For a crossover, they shut off the cold supply to the heater and see whether water still flows from a hot tap. See water heater dip tube failure for more on that part.
Repair or replace
A dip tube, a mixing valve, a shutoff valve, or a faucet cartridge are all modest repairs. Flushing can help a tank with moderate sediment. If an older tank has heavy sediment, rusty water, and slow recovery, replacement may be the better value; a leaking tank is always a replacement.
Frequently Asked Questions
Q: Can a gas valve cause the burner to run but give no hot water? A: Not usually. If the main burner lights and stays lit, the gas valve is delivering gas. The heat is being lost somewhere between the burner and your tap.
Q: How do I know if my dip tube is broken? A: The signs are a short burst of hot water followed by lukewarm, even though the burner keeps running, and small white plastic pieces in faucet screens. A plumber can confirm it by removing the tube.
Q: Will flushing fix a rumbling tank that won’t heat well? A: It can if the sediment is loose. On older tanks the deposits can be hard and won’t flush out; see water won’t drain from the water heater if the drain valve clogs.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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