Water Heater Not Working: Step-by-Step Diagnosis
When a water heater is not working, the cause is usually something cutting off its energy (a tripped breaker, a blown-out pilot, a closed gas valve) or one failed part like an element, thermostat or gas control. Go through the steps below in order. The first three take a few minutes and solve a lot of no-heat problems, and the rest tell you exactly what to say when you phone a plumber.
Step 1: Gas or electric, tank or tankless?
Everything that follows depends on this.
- Gas tank: a flue pipe on top, a gas line and a control knob near the bottom.
- Electric tank: no flue, a thick cable into a junction box on top, and one or two metal access panels on the side.
- Tankless: a wall-mounted box, usually with a digital display.
Note the age while you're there. The serial number on the label usually encodes the manufacture date, and the manufacturer can decode it if it isn't obvious. Rheem puts the typical tank lifespan at about ten years, and that changes how much repair makes sense.
Step 2: Is it every faucet?
Run hot water at the kitchen and at a bathroom sink.
- Cold at one fixture, hot elsewhere: the heater works. The problem is that faucet or shower valve. See no hot water in the shower.
- Lukewarm everywhere: the heater is running but something is weak. Go to water heater not hot enough.
- Cold everywhere: keep going.
Also ask whether the household just used a lot of hot water. A.O. Smith gives recovery times of 30 to 40 minutes for gas tanks and 60 to 90 minutes for electric. Give it that long before you start hunting.
Step 3: Check the energy supply
Electric
Go to the panel and find the double breaker for the water heater. A.O. Smith calls a tripped breaker the most common cause on electric models. Reset it once. If it trips again, leave it off. Something is shorted, often a grounded element, and our breaker keeps tripping page covers what to check next.
If the breaker is on, the red reset button on the upper thermostat may have tripped. A.O. Smith's steps: breaker off, remove the upper access panel, press the red button until it clicks. Full details are on the water heater reset button.
Gas
Look through the sight glass at the bottom of the tank. No flame means the pilot is out. Make sure the gas valve on the supply line is open. If your stove or furnace won't light either, the problem is upstream, so call the gas company.
If the pilot is out, relight it using the instructions on the tank label. If it won't stay lit, the thermocouple is the usual suspect. See pilot light won't stay lit.
If the pilot is burning but the water is cold, the main burner isn't firing. That's its own diagnosis: pilot light lit but no hot water.
Tankless
Read the display. A code on the screen is the fastest path to an answer. For a tankless ignition failure, A.O. Smith says to check the gas supply, venting and ignition pack, and it notes that mineral buildup can clog and damage heating elements. Check that both the gas and water valves under the unit are open.
Step 4: Check the thermostat
Someone may have turned it down. A.O. Smith presets its heaters to 120°F. On gas tanks, the dial is on the gas control valve. On electric tanks, the thermostats are behind the access panels, power off. After you change the setting on a gas heater, A.O. Smith says to wait 30 to 60 minutes for the water to reach the new temperature.
Step 5: Match the symptom to the part
By now you know the heater has energy. What's left is a part. Here's where common symptoms point, from A.O. Smith and Rheem:
| Symptom | Likely part or cause |
|---|---|
| Electric: power on, no heat | Failed element or thermostat |
| Electric: reset button keeps tripping | Grounded element or faulty thermostat |
| Gas: pilot lit, burner won't fire | Faulty gas control valve |
| Gas: poor burner flame | Clogged burner or blocked air screens |
| Hot water runs out fast | Sediment, failed element, broken dip tube |
| Rusty or brown hot water | Corrosion or worn anode rod |
| Rotten egg smell | Bacteria in the tank |
| Water pooled at the base | Internal tank corrosion |
Some of these have their own pages: noises, relief valve leaking, rotten egg smell and rusty hot water.
Step 6: Look for leaks
Check the floor, the drain pan and the pipes on top. A drip from a fitting or the drain valve can often be tightened. Water coming from the bottom of the tank itself usually means the tank has failed and needs replacing. Rheem says pooling at the base usually means internal corrosion, and replacement is the only practical fix. Start at water heater leaking to pin down the source.
When to call a plumber, and what it costs
Call when you smell gas, when a breaker or reset button trips more than once, when the tank itself leaks, or when the fix means working inside electrical or gas controls and you're not comfortable with it. A plumber will appreciate hearing what you've already checked.
HomeGuide's numbers:
| Item | Typical cost |
|---|---|
| Tank repair, typical range | $150 to $700 |
| Tankless repair | $300 to $1,300 |
| Service call fee | $50 to $200 |
| Heating element | $100 to $350 |
| Thermocouple | $100 to $325 |
| Gas control valve | $150 to $550 |
| Tank replacement, installed | $600 to $3,100 |
HomeGuide suggests replacing instead of repairing when the heater is over ten years old or the repair would cost more than half of a new one. See water heater cost for replacement pricing.
FAQ
Why is my water heater not working all of a sudden?
A sudden stop usually means energy was cut off. On electric, that's a tripped breaker or reset button. On gas, it's a pilot that went out or a gas supply problem.
Why is my hot water tank not working when the power is on?
If the breaker is on and the reset button isn't tripped, suspect a failed element or thermostat. Both can be tested with a multimeter with the power off. If you'd rather not open the panels, a plumber can test them in a few minutes.
Should I repair or replace a water heater that stopped working?
Look at age and the repair quote. HomeGuide suggests replacement once a tank passes ten years or a repair costs more than half the price of a new one. HomeGuide says a leak from the bottom of the tank typically means the tank itself is damaged and the heater needs replacing.
Sources
- A. O. SmithWater Heater Not Working? Troubleshooting Guide (opens in a new tab)
- Rheem Manufacturing Company5 Signs Your Water Heater Is Going Bad (And What to Do About It) (opens in a new tab)
- HomeGuideWater Heater Repair Cost (opens in a new tab)
- A. O. SmithHow to Adjust Temperature on Gas Water Heater Safely (opens in a new tab)