Water Heaters troubleshooting: heat, pressure and the sediment underneath.
Gas or electric, tank or tankless, a water heater has a short list of parts and a short list of faults. The two that matter most for safety are the T&P relief valve and a gas smell — everything else can wait for a look with the power or gas off.
First use: what is normal
A new machine can do things on its first run that look like a fault and are not. Here is what the makers say is normal, what to do first, and where the line is.
Normal the first time
- Air sputtering at the hot taps at first, until the lines clear.
Do this first
- 1Never power or light it before the tank is full. An element burns out almost at once in a tank that is not full.
- 2Open a hot tap and let it run until the flow is steady, then turn it on. An electric one takes at least an hour to heat.
Where the line is. A dripping relief valve is not normal, and neither is a gas smell or water on the floor: shut it off and text us.
Before you touch anything
The install rules that decide most of what follows. Check these once; they rule out the causes that look like a broken machine and are not.
A tank heater needs a drain pan with a drain line, a T&P relief valve piped to within six inches of the floor, and an expansion tank on a closed system. Those are code, not options.
Electric: a dedicated 240V, 30A double breaker, and the tank FULL before the breaker goes on — an element powered dry burns out in seconds.
Gas: the vent sloping up to the flue with no gaps, the gas valve open, and the thermostat set no higher than 120°F.
No hot water (electric)
In this order
- Reset the double breaker fully off and then on.
- Press the red high-limit reset button behind the upper access panel (power off first).
- Was the tank filled before the power went on?
- Any sign of water at the lower element?
What is usually behind it
A tripped breaker or high-limit, a burnt upper element (powered dry, or just worn), or a failed upper thermostat.
What to do
Reset the breaker and the high-limit. If the high-limit trips again, an element or thermostat has failed — the elements are tested with a meter across their terminals, power off, and replaced with the tank drained.
Any work behind the access panels is done with the breaker OFF and checked with a meter — 240V with wet hands is a hospital trip.
No hot water (gas) or the pilot will not stay lit
In this order
- Is the gas valve at the heater open?
- Is the pilot lit (look through the sight window)?
- Does the pilot light and then go out when you release the button?
- Is the status light blinking a code (newer units)?
What is usually behind it
A closed valve, a pilot blown out, a worn thermocouple or flame sensor (pilot dies when the button is released), or a dirty burner assembly.
What to do
Relight the pilot by the steps on the tank's label. A pilot that will not stay lit after two tries is the thermocouple — a cheap part, but a gas tech's job on a sealed-combustion unit.
Gas smell: close the valve, open a window, do not relight, and call.
Runs out of hot water fast
In this order
- Is the thermostat set to 120°F (lower on a new unit's factory setting)?
- Electric: does the water go lukewarm after a short while? That is the lower element.
- Has the tank been flushed in the last year?
- Is the tank the right size for the house?
What is usually behind it
A low thermostat, a failed lower element (electric), a tank full of sediment, or a tank too small for the demand.
What to do
Set 120°F, flush the tank from the drain valve until it runs clear, and test or replace the lower element. A 40-gallon tank cannot run two showers and a dishwasher at once, whatever is fixed.
Rumbling, popping or crackling
In this order
- When was the tank last flushed?
- Does the noise come while heating?
- Is the water hard?
What is usually behind it
Sediment on the tank bottom — water trapped under it boils and pops. Harmless at first, but it burns out elements and the tank over time.
What to do
Flush the tank: power or gas off, cold supply off, hose on the drain valve to a floor drain, open a hot tap upstairs, drain until clear. Twice a year on hard water.
Water dripping from the relief valve or the pan
In this order
- Is the drip from the T&P valve's pipe, the drain valve, a fitting on top, or the tank itself?
- Is there an expansion tank on the cold line, and is it hanging limp (waterlogged)?
- Is the thermostat set above 130°F?
What is usually behind it
Pressure in a closed system with no working expansion tank (the T&P valve does its job), a thermostat set too high, a loose fitting, or a tank that has started to leak.
What to do
Turn the heat down to 120°F, have an expansion tank installed or replaced, tighten a fitting. Water from the tank seams or the bottom is the end of the tank.
Never cap or plug a T&P valve. Steady water from the tank body means the tank is failing — shut the water and the power or gas, and plan the replacement.
Hot water smells like rotten eggs
In this order
- Does the cold water smell too? Then it is the well or the supply, not the heater.
- Is the house on a well or softened water?
- How old is the anode rod?
What is usually behind it
Sulfur bacteria reacting with the magnesium anode rod in the tank — common on wells and softeners.
What to do
Replace the anode with an aluminum-zinc or a powered anode, and flush the tank with a peroxide treatment once. The anode is a large hex nut on top of the tank — a plumber or a strong arm with a breaker bar.
Water too hot or scalding
In this order
- Thermostat setting? 120°F is the right number for a house.
- Electric: are both thermostats set the same?
- Does the heater cycle off at all?
What is usually behind it
A thermostat set high, or a thermostat stuck closed and never cycling off.
What to do
Set 120°F. A tank that keeps climbing past the setting has a stuck thermostat — replace it before the T&P valve has to open.
Water over 140°F at the tap with the thermostat set low: shut the power or gas off and call — a stuck thermostat is a scald and a pressure hazard.
When it's a warranty call
Every unit leaves with the manufacturer's full factory warranty. These are the faults that warranty exists for — once the checks above have ruled out the install, the power and the vent, call the maker's line with the model and serial, and text us if you want a hand with the claim.
A tank that leaks from its body or seams — the tank itself carries the factory warranty by year.
A gas control valve or a sealed burner assembly that will not fire with the gas on.
A tankless unit that throws a code the manual's reset does not clear.
All units are surplus inventory (open box, cancelled order, customer return, overstock, or minor scratch & dent). Every unit includes the manufacturer's full factory warranty. Please inspect thoroughly in person before purchasing — cosmetic imperfections or missing accessories are possible.
Text us the model number and what it's doing — we'll point you at the next step.
A fix, a part, or a warranty call — the plate's model and serial plus one line about the symptom is all it takes to tell which.
These pages are educational. Every appliance is a little different — follow the manufacturer's manual and local code, and leave gas, water heater and 240V work to a licensed installer.