Water Heater Leaking? What to Shut Off First, Then 5 Causes

Water on the floor by the heater, and you assume the tank is finished. Usually not. Four of the five things that leak bolt to the outside, and those parts run $3 to $25. What costs you is waiting for 50 gallons to drain and cool.

Shut These Off Before You Do Anything Else

1. 1Kill the energy first. Electric: flip the double pole breaker labelled for the water heater, usually 30 amp but not on every panel, then confirm the heater is dead. Gas: knob to OFF.
2. 2Leave the cold supply on for now, the valve on the pipe into the tank top. Close it only if water is pouring out.
3. 3Dry the whole heater, fittings on top included, then lay paper towel around the base. A condensate line or a washer pan drips onto the same floor, so rule those out.
4. 4Wait 30 minutes. Wet at the top is a connection or the T&P valve: trace its discharge pipe to see if it ran. Wet at the bottom is not the tank yet: it is the drain valve, condensation, or the tank, and sections 2, 4 and 5 separate them.
5. 5Close that cold supply and open a hot tap before you touch the wet part. If the valve will not move, shut the house main.

1. The T&P Valve Is Doing Its Job

1. 1The valve sits on top or in the upper side port, discharge pipe to the floor, and a wet pipe means it opened. Screw a $12 pressure gauge onto an outside hose bib: over 80 psi is above code and pops it.
2. 2High reading? The fix depends on whether your system is closed. Look where the main enters for a pressure reducing valve or a backflow preventer. None fitted means expanded water still escapes back into the main, so the street pressure itself is the problem: a pressure reducing valve, $350 to $600. One fitted means the system is closed and heated water has nowhere to go, spiking the pressure every cycle: a $50 to $70 expansion tank.
3. 3Hold a thermometer under the nearest hot tap. 120 to 140 F is normal. 180 F or hotter is a runaway thermostat: stop and call a plumber.
4. 4Only when pressure and temperature both read normal is the valve itself bad. Kill the energy first: electric, the double pole breaker; gas, knob to OFF. Run the nearest hot tap until the water goes cold. Then close the cold supply, open a hot tap to vent the pressure to zero, and drain a few gallons until the level is below the T&P port. With the water still on, that port throws 140 F at house pressure into your face.
5. 5A 3/4 inch, 150 psi, 210 F replacement is $15 to $25 on four wraps of PTFE tape. Refill with a hot tap open until it runs without spitting air. Never re-energise a tank that is not full. Hands clear, then restore the energy. On gas, wait five minutes, then put your nose at floor level. Any gas smell: leave the house and call the utility from outside. No smell, relight by the label. Three failed tries, leave it off and call a plumber.

2. The Drain Valve at the Bottom Is Weeping

1. 1Kill the energy before you put a hand on this tank. Electric: the double pole breaker for the water heater. Gas: knob to OFF. Leave the cold supply on for the towel test.
2. 2Dry the valve, wrap a paper towel round it, look in an hour. A wet towel over a dry floor names the cheapest part on the heater, not a dead tank.
3. 3Try the three dollar fix first: a brass hose cap with a rubber washer, hand tight on the outlet.
4. 4If it drips from behind the handle, the valve has to come out, with the energy still off. Run the nearest hot tap until the water goes cold, so you are not sending 140 F through a garden hose. Close the cold supply and open a hot tap so the tank vents as it empties. Now hose it outside, 20 to 40 minutes on a 50 gallon tank. Support an old plastic valve as you turn it; the housing cracks.
5. 5Thread in a brass ball valve, $15 to $20, on four wraps of PTFE tape. Snug it, then a quarter turn and no more.
6. 6Refill with a hot tap open until it runs without spitting air. Never put energy back into a tank that is not completely full. Stand clear, then flip the breaker on. On gas, wait five minutes, then put your nose at floor level. Any gas smell: leave the house and call the utility from outside. No smell, relight by the label. Three failed tries, leave it off and call a plumber.

3. A Connection at the Top Is Leaking

1. 1Kill the energy before a wrench goes near the top of this tank. Electric: the double pole breaker for the water heater. Gas: knob to OFF. Then run the nearest hot tap until the water goes cold, so what sits behind the fitting is no longer 140 F. Leave the cold supply on for the towel test only, closing it the moment you pick up a wrench.
2. 2Dry both fittings and the shutoff, then press a paper towel on each. The one that stains is yours, often a flex line as old as the house.
3. 3Found it? Close the cold supply and open a hot tap to drop the pressure to zero. Now a wrench on the fitting, a second on the nipple below as backup, and a quarter turn, no further. Twisting the nipple turns a drip into a flood.
4. 4Still weeping? With the supply still closed and a hot tap still open, drain below the fittings, unscrew the joint, and rewrap the male thread with four wraps of PTFE tape. Green or white crust on the braid means it will not seal again: fit a new braided line, $15.
5. 5A drip off the shutoff stem is different: snug its packing nut an eighth of a turn, same as a dripping faucet.
6. 6Hands off the joint, then open the cold supply slowly and watch it fill. Only with the tank full and the joint dry do you restore the energy. On gas, wait five minutes, then put your nose at floor level. Any gas smell: leave the house and call the utility from outside. No smell, relight by the label. Three failed tries, leave it off and call a plumber.

4. It Is Condensation, Not a Leak

1. 1A cold tank in a warm room sweats. Water that shows during a long draw and is gone two hours later is condensation.
2. 2Check the setpoint. On gas it is a dial on the control valve outside the tank, nothing to open. On electric it sits behind a screwed panel with live 240 volt terminals beside it: flip the double pole breaker, confirm both legs are dead with a non-contact tester before your hand goes past the cover, and screw the panel shut before the breaker goes back on.
3. 3Below 120 F the tank never gets warm enough to stop sweating. 120 F at the tap will not scald, and 140 F with a mixing valve covers bacteria.
4. 4On gas, a lazy yellow flame and sizzling at the burner mean condensate is landing on it. Look through the sight port, cover on.
5. 5Water still there once the tank is hot is a real leak: check the fittings on top.

5. The Tank Has Rusted Through

1. 1Shut the energy off before you go near a heater standing in its own water. Electric: the double pole breaker for the water heater. Gas: knob to OFF. Never kneel in the puddle with the breaker on.
2. 2Read the rating plate for the manufacture date. A serial alone is brand specific and several makers code the year as a letter, so look yours up rather than guess. Past 10 years with a bottom leak, it is the tank.
3. 3Look under the heater with a flashlight, not at the puddle. Rust streaks from the seam or a rusty ring in the pan confirm it.
4. 4Run the nearest hot tap until the water goes cold, so you are not sending 140 F through a garden hose. Then close the cold supply, leave that hot tap open so the tank vents as it empties, and hose it outside. Fifty gallons on a finished floor costs more than the heater.
5. 5Budget $1,200 to $2,200 fitted for a 40 to 50 gallon swap, more if venting needs redoing.
6. 6On the new one, calendar the anode rod: it corrodes so the steel does not. Check it at year three, $30 to $50, not another tank. A spent rod also makes hot water smell like rotten eggs.