Water Heater
Water Heater Not Working? Here's How to Find Out Why
Last verified September 17, 2026
Quick Answer: Likely Causes
- Electric: tripped breaker or blown fuse (the most common cause on electric units)
- Electric: failed heating element (upper or lower)
- Gas: pilot light out
- Gas: failed thermocouple (the most common reason a pilot won't stay lit)
- Both: thermostat set too low, or sediment buildup reducing efficiency
Where to Start
Gas and electric water heaters fail through completely different components, so identify which you have before diagnosing further. Electric starts at the breaker panel. Gas starts at the pilot assembly. A few causes — thermostat setting, sediment buildup, a leaking tank, a faulty pressure-relief valve — apply to both types.
Safety Notes
- If you smell gas anywhere near the water heater, do not attempt to relight the pilot or do anything else yourself. Shut off the gas supply and call for professional help immediately.
- A leaking or stuck pressure-relief valve is a safety device, not a routine part — this needs immediate professional attention, not a DIY fix.
If your water heater isn’t producing hot water at all, the fastest way to narrow this down is knowing whether you have a gas or electric unit — the two fail through entirely different components, and troubleshooting the wrong system wastes time.
Gas or electric — this determines your starting point
Electric: start at your home’s breaker panel. A tripped breaker is the single most common cause of an electric water heater not working, and it takes seconds to check.
Gas: start at the pilot light. If it’s out, that’s very likely your answer — but how you get it relit, and why it might not stay lit, matters for diagnosing the real cause underneath.
A few causes apply to both types regardless of which path you’re on: thermostat setting, sediment buildup in the tank, a leaking tank, or a faulty pressure-relief valve. Work through the type-specific checks below first, then consider these if the basics don’t resolve it.
Diagnostic Steps
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Electric: check the breaker and fuse
- What to look for
- A tripped breaker or blown fuse at the electrical panel.
- What it indicates
- This is the single most common cause of an electric water heater not working at all — and the fastest to rule out.
- What to do
- Reset the breaker. If it trips again immediately, that's a sign of a deeper electrical issue and needs a licensed technician rather than repeated resetting.
- If nothing changes
- Check the thermostat setting.
Gas: check the pilot light
- What to look for
- Whether the pilot flame is lit.
- What it indicates
- If the pilot's out, the burner has no way to ignite and the unit won't produce hot water.
- What to do
- Follow the relighting instructions on the water heater's label exactly. If you smell gas at any point, stop and follow the safety note above instead.
- If nothing changes
- If the pilot won't relight or won't stay lit, check the thermocouple.
Check the thermostat setting
- What to look for
- The set temperature — applies to both gas and electric units.
- What it indicates
- Anything set below roughly 90°F effectively means no usable hot water, even though the unit is technically working. 125°F is a commonly recommended setting that balances usable hot water with safety and efficiency.
- What to do
- Adjust to the recommended setting and give it time to recover.
- If nothing changes
- Electric: test the heating elements. Gas: inspect the thermocouple.
Gas: inspect the thermocouple
- What to look for
- Visible discoloration, cracks, or holes, and whether it's making proper contact with the pilot flame.
- What it indicates
- A faulty thermocouple is the most common reason a pilot light won't stay lit — it's a safety device that shuts off gas flow if it doesn't sense the pilot burning, so a worn one can shut things down even when the pilot itself is fine.
- What to do
- This is a low-cost, straightforward replacement in many cases — check that it's properly seated in the flame first before assuming it needs replacing.
- If nothing changes
- If replacing the thermocouple doesn't resolve it, the gas control valve may be at fault — this is technician territory.
Electric: test the heating elements
- What to look for
- Upper and lower elements — a failed lower element in particular is a common cause of water that's lukewarm rather than fully cold, since the upper element may still be working.
- What it indicates
- Either element failing reduces or eliminates hot water production, and it's usually noticeable fairly quickly.
- What to do
- Element testing and replacement is a common repair, though it involves working inside an electrical appliance connected to a full water tank — many homeowners have this done professionally.
- If nothing changes
- Consider sediment buildup as a contributing factor.
Consider sediment buildup
- What to look for
- Reduced efficiency or slower recovery even after other checks pass, especially on an older unit that's never been flushed.
- What it indicates
- Mineral deposits settle at the bottom of the tank over time and insulate the water from the heat source, reducing how effectively the unit heats.
- What to do
- A tank flush can help — this is routine maintenance worth doing periodically regardless of whether it's the current problem.
- If nothing changes
- N/A.
What Not to Do
- Don't attempt to relight a gas pilot if you smell gas — shut off the supply and call for help instead.
- Don't ignore a leaking or stuck pressure-relief valve.
When to Call a Professional
- A tripped breaker that trips again immediately after resetting
- Leaking tank (usually corrosion or worn fittings — this typically means replacement rather than repair)
- Faulty pressure-relief valve
- Gas control valve suspected after thermocouple replacement doesn't resolve the issue
- Any gas smell near the unit
Repair vs. Replace
A thermocouple, heating element, or thermostat is a low-cost, straightforward repair in most cases. A leaking tank almost always means replacement rather than repair, since tank corrosion can't be fixed. A gas control valve replacement or a unit past its typical 8-12 year lifespan is worth weighing against the cost of a new water heater before committing to repair.
Frequently Asked Questions
My pilot light keeps going out repeatedly — what's actually wrong?
By far the most common cause is a worn thermocouple. It's inexpensive and often a straightforward DIY replacement, but confirm there's no gas smell or other complication before working on it yourself.
Is it normal for a water heater to run out of hot water faster than it used to?
This pattern — hot water that used to last but now runs out quickly — often points to a failed lower heating element (electric) or sediment buildup reducing tank capacity/efficiency (either type).
How do I know if I need a repair or a whole new water heater?
A leaking tank is generally a replacement situation rather than a repair, since tank corrosion doesn't get fixed. For other issues — a thermocouple, an element, a thermostat — repair is usually the more practical route.