Water Heater Troubleshooting: Fix Common Problems Yourself

When Your Water Heater Acts Up

Few household problems are as immediately noticeable as losing hot water. Whether you are dealing with no hot water at all, water that is not hot enough, strange noises from the tank, or a puddle on the floor, most water heater issues have identifiable causes and — in many cases — fixes that a homeowner can handle without calling a plumber.

This guide covers the most common water heater problems, their likely causes, and what you can do about each one. It applies to both gas and electric tank-style water heaters, with a section on tankless units at the end.

Safety First

Water heaters involve high temperatures, electrical connections, and (for gas models) combustible fuel. Before working on your water heater:

• Know where your gas shut-off is. For gas water heaters, there is a gas valve on the supply line near the bottom of the unit. Turn it to the OFF position before doing any work. If you smell gas at any time, leave the house and call your gas utility company immediately.
• Turn off the power. For electric water heaters, turn off the dedicated breaker at your electrical panel. Electric water heaters run on 240 volts, which is dangerous.
• Be aware of scalding. Water inside the tank can be 120 to 140 degrees or higher. Open the pressure relief valve carefully and let water cool before draining.

Problem: No Hot Water at All

This is the most common complaint, and the cause depends on whether you have a gas or electric unit.

Gas Water Heater — No Hot Water

1. Check the pilot light. On older gas water heaters with a standing pilot light, look through the small window at the bottom of the unit. If you do not see a small flame, the pilot has gone out. Follow the relighting instructions printed on the water heater label. Typically, you turn the gas valve to PILOT, hold down the reset button, and use the built-in igniter or a long lighter to ignite the pilot. Hold the button for 30 to 60 seconds after the pilot lights, then turn the gas valve to ON.
2. Check the thermocouple. If the pilot light will not stay lit after you release the reset button, the thermocouple is likely faulty. The thermocouple is a small copper tube that extends from the gas valve to the pilot flame. Its tip should sit directly in the pilot flame. If it is bent away from the flame, gently bend it back. If it is corroded or the pilot still will not stay lit, replace the thermocouple — a $10 to $20 part available at any hardware store. Unscrew the old one from the gas valve, remove it from its bracket, and install the new one.
3. Check the gas supply. Make sure the gas valve on the supply line is in the ON position (handle parallel to the pipe). Check that other gas appliances in the house are working to confirm gas service is active.

Electric Water Heater — No Hot Water

1. Check the breaker. Go to your electrical panel and look for the breaker labeled for the water heater. If it has tripped (sitting in the middle position), flip it fully to OFF, then back to ON.
2. Reset the high-temperature cutoff. Electric water heaters have a reset button (also called the ECO or high-limit switch) on the upper thermostat, located behind an access panel on the side of the tank. Remove the panel, push aside any insulation, and press the red reset button. If it clicks, the cutoff had tripped. Replace the panel and wait 30 to 60 minutes for the water to heat.
3. Test the heating elements. Electric water heaters have two heating elements — an upper and a lower. If one fails, you may get lukewarm water or no hot water. Testing requires a multimeter: turn off the breaker, remove the access panels, disconnect one wire from each element, and test for continuity. A good element shows low resistance (10 to 30 ohms). An open circuit (infinite resistance) means the element is burned out. Replacement elements cost $10 to $25 and screw into the tank. Drain the tank below the element level before removing it.

Problem: Not Enough Hot Water

If you get hot water but it runs out too quickly:

• Check the thermostat setting. The recommended setting is 120 degrees Fahrenheit. If someone turned it down, you will run out faster. On a gas unit, the thermostat is the dial on the gas valve. On an electric unit, adjust the thermostat behind the access panels using a flathead screwdriver.
• Sediment buildup. Over time, minerals in the water settle at the bottom of the tank, reducing the effective capacity and insulating the water from the heating element or burner. Flushing the tank removes this sediment (see maintenance section below).
• A failing lower heating element (electric units). If the lower element has failed, only the upper element heats the water, effectively cutting your hot water supply in half.
• Tank too small for demand. If your household has grown or usage patterns have changed, your current tank may simply be undersized. A family of four typically needs a 50-gallon tank.

Problem: Water Is Too Hot

Water that comes out scalding hot is a safety hazard, especially for children and elderly household members.

1. Check the thermostat and lower it to 120 degrees if it is set higher.
2. On an electric water heater, a faulty thermostat can fail in the "on" position, causing continuous heating. If lowering the setting does not help, the thermostat may need replacement. This is a job best left to a qualified plumber or electrician.
3. The pressure relief valve (T&P valve) is a critical safety device on the side of the tank. If the water temperature or pressure exceeds safe levels, this valve opens to release water and prevent a dangerous pressure buildup. If you notice water dripping from the T&P valve discharge pipe, it may indicate the water is overheating or the valve itself is faulty. Do not cap or plug this valve — call a professional.

Problem: Strange Noises

Popping or Rumbling

This is the most common water heater noise and is caused by sediment buildup on the bottom of the tank. When the burner heats the water trapped under the sediment layer, it creates steam bubbles that pop as they rise through the sediment. The fix is to flush the tank.

Sizzling or Hissing (Gas Units)

On a gas water heater, a sizzling sound can indicate condensation dripping onto the hot burner assembly. This is common during heavy draw periods and is usually harmless. However, if the sizzling is constant, check for a small leak at a fitting or the T&P valve.

High-Pitched Whining (Electric Units)

Electric elements can accumulate scale, which causes the element to work harder and produce a whining or humming sound. Flushing the tank and replacing scaled elements resolves this.

Problem: Rusty or Discolored Water

If hot water is rusty or brown but cold water is clear, the problem is inside the water heater, not in the municipal supply.

• Corroding anode rod. The sacrificial anode rod is a metal rod (usually magnesium or aluminum) that hangs inside the tank and corrodes instead of the tank walls. Once the rod is fully consumed, the tank itself begins to rust. Check the anode rod by unscrewing it from the top of the tank with a 1-1/16 inch socket. If it is less than half an inch in diameter or coated in calcium, replace it. New anode rods cost $20 to $50.
• Corroding tank. If the anode rod has been depleted for a long time, the tank lining may be corroding. At this stage, the tank cannot be repaired and will eventually leak. Plan for replacement.

Problem: Leaking Water Heater

A leak can range from a minor drip to a serious flood. Where the leak is coming from determines whether it is fixable.

• Leaking from fittings at the top. Check the cold water inlet and hot water outlet connections. Tighten the fittings or replace corroded flex lines. This is usually a simple fix.
• Leaking from the T&P valve or its discharge pipe. The valve may be releasing excess pressure (indicating a thermostat or pressure problem) or the valve itself may be faulty. Replace the T&P valve — a $10 to $20 part that threads into the tank.
• Leaking from the drain valve at the bottom. Tighten the valve or replace it if it is dripping. A brass replacement drain valve costs about $10.
• Leaking from the tank body. If water is seeping from the tank itself (not from a fitting, valve, or connection), the tank is corroded through. There is no repair for this — the water heater needs to be replaced. Turn off the gas or electricity and the water supply, and call a plumber or begin replacement.

Essential Maintenance: Flush the Tank

Flushing your water heater annually removes sediment, improves efficiency, and extends the life of the unit. It takes about 20 minutes.

1. Turn off the gas valve or the electrical breaker.
2. Connect a garden hose to the drain valve at the bottom of the tank. Run the hose to a floor drain, driveway, or bucket.
3. Open the T&P valve lever or open a hot water faucet upstairs to allow air into the tank.
4. Open the drain valve. Let the water flow until it runs clear. If the water is very sediment-heavy, you may need to close the drain, let the tank refill partially, and drain again.
5. Close the drain valve, remove the hose, close the T&P valve, turn the cold water supply back on, and let the tank fill completely before restoring gas or power. Running a gas burner or electric element on an empty or partially filled tank will cause damage.

Tankless Water Heater Troubleshooting

Tankless (on-demand) units have their own set of common issues:

• No hot water or unit does not ignite. Check that the gas supply or electrical breaker is on. Verify that the minimum flow rate is met — most tankless units require at least 0.5 gallons per minute of flow to activate. A partially closed fixture or low water pressure can prevent ignition.
• Fluctuating temperatures. This often results from running too many fixtures simultaneously, exceeding the unit's capacity. It can also indicate scale buildup on the heat exchanger. Flush the unit with a vinegar descaling kit annually.
• Error codes. Tankless units display error codes on their digital panels. Consult the owner's manual for your specific model. Common codes relate to ignition failure, exhaust blockage, or overheating.

When to Call a Professional

Handle simple tasks like relighting a pilot, flushing the tank, replacing an anode rod, or swapping a thermocouple yourself. Call a licensed plumber for:

• Gas line connections or gas valve replacement
• Tank replacement or new installation
• Persistent T&P valve discharge (indicates a pressure or temperature problem that needs diagnosis)
• Any situation where you smell gas
• Electric water heater work if you are not comfortable with 240-volt wiring

A well-maintained water heater works quietly in the background for a decade or more. A few minutes of annual maintenance and prompt attention to problems will help you get the full life out of your unit.