The essentials in 30 seconds
First, make it safe: switch off the power (electric) or set the gas control to off (gas), then close the cold-water valve above the heater. Dry the tank and floor, wait, and watch where fresh water appears. Top leaks usually come from the cold inlet or hot outlet fittings, the anode port or the temperature and pressure (T&P) relief valve. Bottom leaks come from the drain valve, the relief valve's discharge pipe, condensation on a gas model, or the tank itself. Valves and fittings can be replaced; a tank leaking through its own steel wall cannot be repaired and needs replacing. Most storage water heaters last 10 to 15 years.
- Water running from the T&P relief valve can be scalding hot and signals excess temperature or pressure: call a plumber.
- If you smell gas, leave the house first and call from outside.
- In British homes the tank is usually called a hot water cylinder; the same checks apply to its valves and fittings.
What to do right now
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01
Cut the energy
Electric heater: switch off its breaker at the panel. Gas heater: turn the gas control on the heater to off, following the label on the unit. If the floor around the panel is wet, see the safety box above.
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02
Close the cold supply
Turn the cold-water valve on the pipe entering the top of the heater fully clockwise. This stops the tank refilling, so a leak slows or stops.
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03
Protect the area
Move boxes and rugs, put towels or a tray under drips and run a wet vacuum over standing water.
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04
Let it cool
The tank holds hot water under pressure. Give it time before you touch fittings or open any valve.
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05
Find the source
Dry the tank, the pipes and the floor completely, then follow the map below. A sheet of paper towel under each fitting shows which one is dripping.
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06
Decide
Small drips at a valve or fitting can wait a day for a plumber with the heater off. Water coming from the tank body, or a relief valve that keeps discharging, needs attention the same day.
Where the leak comes from
Start at the top of the heater and work down: water runs downward, so a puddle at the base may come from a fitting higher up.
| Where you see water | Likely cause | What to do |
|---|---|---|
| Cold inlet or hot outlet pipes on top | Loose or corroded fitting, worn connector | Plumber tightens or replaces the fitting or flexible connector |
| Anode rod port on top | Worn seal or corroded fitting around the sacrificial anode rod | Plumber reseals the port, often replacing the rod at the same time |
| T&P relief valve (side or top) dripping | Excess pressure from thermal expansion, high supply pressure, thermostat set too high, worn valve | See the relief valve section; plumber checks pressure and the valve |
| End of the relief valve discharge pipe | Same as above: the valve is releasing water | Never cap the pipe; call a plumber |
| Drain valve near the bottom | Valve left slightly open, worn washer, sediment on the seat | Close it gently and fit a hose cap; plumber replaces a worn valve |
| Drips on the burner of a gas heater, sizzling | Condensation when a refilled tank is cold, or a leak above | If it stops once the tank is hot and the floor stays dry, it is condensation; if water keeps pooling, treat it as a leak |
| Water seeping from the base or through the jacket, fittings dry | Tank corroded through | Replace the heater |
| Rusty water and rust streaks on the tank | Advanced corrosion | Plan replacement soon |
| Puddle with nothing wet on the heater | Another source: nearby pipes, AC condensate line, washer, floor drain | Check neighbors of the heater and the AC drain |
Leaking from the top
Top leaks are the most fixable. Fittings loosen and corrode over time, and the joints where the cold inlet, hot outlet and anode rod enter the tank are the usual suspects. Dry them, wait, and look for the first bead of water. Dripping from a fitting at the top can also run down inside the insulation and appear at the bottom, which is why a "bottom leak" deserves a check of the top first.
Leaking from the bottom
Look at the drain valve first: a valve that was not fully closed after flushing, or a worn washer, will drip steadily. Next, check whether the water comes down the relief valve discharge pipe. If both are dry and water still seeps from under the jacket, the tank itself is probably leaking.
Water heater pressure relief valve leaking
The temperature and pressure relief valve opens to release water when the temperature or pressure in the tank goes too high. It is an emergency safety device, not something meant to operate every day, and discharge from it can be very hot.
Common reasons it drips:
- Thermal expansion. Water expands as it heats: in a 40-gallon heater, by about half a gallon. If a check valve, backflow preventer or pressure-reducing valve on your supply line makes the system "closed", that extra volume has nowhere to go. A sign of thermal expansion is the valve releasing about one cup per 10 gallons of tank size with each heating cycle. The usual fix is a thermal expansion tank fitted by a plumber.
- High water pressure. If dripping continues after an expansion tank is fitted, have the supply pressure checked. Above about 75 psi, a pressure regulator on the incoming line is the usual answer.
- A worn or scaled valve. Repeated discharges leave mineral deposits on the valve seat, which can stop it sealing, or stop it opening when needed.
- Thermostat set too high. The CPSC recommends 120°F (49°C) for scald safety, a temperature the US Department of Energy also describes as safe for most people.
The discharge pipe must run downward from the valve to a drain, end in plain view a short distance above it (HUD inspection standards look for 2 to 6 inches above the drain's flood level) and must never be capped, threaded at the end or fitted with a shut-off valve. Those rules exist so the valve can always release and so you can see when it does.
Gas and electric heaters: what differs
| Point | Gas heater | Electric heater |
|---|---|---|
| How to switch it off | Gas control on the heater to off; supply shut-off valve on the gas line | Breaker at the panel |
| Extra checks | Water dripping on the burner; rust or water around the flue | Water near the access panels, thermostats and wiring |
| Specific risks | Gas leaks; a blocked, rusted or misaligned flue can let combustion gases into the home | Shock risk when water reaches wiring |
| Before restarting | Follow the lighting instructions on the label once the leak is fixed | Make sure the tank is full of water before restoring power |
On a gas heater, check the flue pipe above the heater while you are there. HUD treats a blocked, misaligned or missing flue as life-threatening, because it can vent dangerous gases into the home, and metal tape is no substitute for a proper flue connection. If water has dripped onto the burner or around the flue, have a gas technician check both before relighting.
On an electric heater, the tank must always be full of water before the power goes back on, so the elements are covered. Most electric heaters have two thermostats behind access panels, and the CPSC advises switching off the breaker before removing those panels.
When the tank must be replaced
| Finding | Usually |
|---|---|
| Dripping inlet, outlet or anode port fitting | Repair |
| Dripping drain valve | Repair |
| T&P valve dripping, tank fine | Fix the cause (expansion tank, pressure regulator, thermostat) and replace the valve if worn |
| Water seeping from the tank wall or base | Replace the heater |
| Rusty hot water plus a leak, tank near or past 10 to 15 years | Replace the heater |
Regular maintenance helps the next tank last. The Department of Energy suggests draining about a quart from the tank every three months to clear sediment that hinders heat transfer, following the manufacturer's directions. The anode rod is designed to corrode instead of the tank; ask your plumber to check it at service visits.
Drying the area afterwards
Dry the floor, walls and anything stored near the heater within 24 to 48 hours to prevent mold (mould) growth, following EPA advice. Cardboard boxes, carpet and drywall that stayed wet longer may need to go. A moisture sensor beside the heater warns you early next time: see our guide to water leak detectors. If the heater sits in a loft or upper floor and water came through, read our ceiling leak guide.
What to ask the plumber
- Where exactly is the water coming from, and can that part be replaced on its own?
- Is the system closed, and do I need a thermal expansion tank?
- What is my water pressure at the inlet?
- What condition is the anode rod in, and how much sediment is in the tank?
- If replacing: will the new relief valve discharge pipe run correctly to a drain?
Water heater leaking: frequently asked questions
Why is my water heater leaking from the bottom?
The most common sources are the drain valve, water running down from a fitting at the top, the relief valve pipe, or a corroded tank. Dry everything and watch where water first appears.
Why is my water heater leaking from the top?
Usually a loose or corroded cold inlet or hot outlet fitting, the anode rod port, or the relief valve. These parts can generally be replaced.
Is a leaking water heater dangerous?
It can be. Hot water scalds, water near wiring brings shock risk, and a relief valve that discharges signals high temperature or pressure. Switch the heater off and call a plumber.
Can I still use a leaking water heater?
Switch it off and close the cold supply until the source is found. A small drip from a fitting can wait for a plumber; a tank leak or discharging relief valve needs prompt attention.
Is it normal for the pressure relief valve to drip?
Occasional drips often mean thermal expansion or high supply pressure. It is a warning sign worth a plumber's visit.
Can a leaking water heater tank be repaired?
Valves and fittings can. A tank leaking through its own steel wall needs replacing.
How long do water heaters last?
Most storage water heaters last about 10 to 15 years; tankless models can last more than 20, according to the US Department of Energy.
Sources
Official and safety guidance, checked on 27 October 2026.
- HUD · NSPIRE standard: water heater ↗Relief valve leaks and discharge piping (downward slope, never capped, 2 to 6 inches above the drain), flue and gas shut-off deficiencies.
- City of Tavares, FL · Temperature and pressure relief valves ↗Thermal expansion figures, signs of expansion, 75 psi, annual lever test, three-year inspection and discharge line rules.
- US CPSC · Avoiding tap water scalds ↗120°F setting, burn times and switching off electric heaters before adjusting thermostats.
- US Department of Energy · Energy Saver guide ↗Draining sediment every three months, 120°F and lifespan of storage and tankless heaters.
- Kansas Corporation Commission · Natural gas safety ↗What to do if you smell gas.
- US EPA · A brief guide to mold, moisture and your home ↗Drying wet materials within 24 to 48 hours.
Found a puddle by the heater?
Switch it off, close the cold valve and take a photo of the wet fittings before the plumber arrives.