The water heater is leaking — find the source, then act
Not all water-heater leaks are equal: some come from a fitting you fix with a light nudge, and some come from the tank body itself, which means the tank is finished and has to be replaced. The whole job is finding exactly where it's leaking before you touch anything — and before even that, cutting the power and shutting the water, because the water inside can be scalding and an electric heater sits on the mains.
The problem
You can see water under or around the heater, or dripping from the top at the fittings, or a stream running out of the safety valve (T&P) on the side. Sometimes it's a damp patch on the ceiling under a rooftop solar tank, or rust and beading on the tank body itself. The key thing to establish: a leak from a fitting is not the same as a leak from the tank body — the first is fixable, the second means the tank is done.
Likely causes
The T&P (safety) valve dripping
Every heater has a temperature-and-pressure relief valve (T&P) that releases water if pressure or temperature climbs too high, with a discharge pipe running down from it. A brief drip after the water heats up can be normal thermal expansion; but a steady drip means the valve is fouled, faulty, or your mains pressure is too high. Never plug it — it's the safety valve that stops the tank exploding.
Loose inlet/outlet fittings
The copper or flexible connectors on top of the heater (cold in, hot out) work loose over time from heating and cooling. This is the most common leak you can fix at home: a drip only at the connector nut, with the tank itself sound. Usually a light tighten or fresh thread tape stops it.
A leaking drain valve at the bottom
At the base of the tank is a small valve for draining and flushing. Over time it collects grit or its rubber seat wears, so it weeps. Sometimes it's just loose and tightens up; sometimes it needs replacing — a cheap part and a fairly easy swap once the tank is empty and cold.
A corroded / failed tank (terminal)
If water is weeping from the tank body itself or from the seam weld down its side, the tank has rusted through from the inside and is finished. This leak cannot be fixed — not with a weld, not with sealant. The whole tank must be replaced. Corrosion runs faster in hard, salty-water areas, which covers much of the Gulf and Egypt.
A worn element gasket (electric)
The heating element is bolted to the tank body with a rubber gasket; if that gasket perishes, water weeps from around the element flange. Diagnosing it is fine, but replacing it means draining the tank and removing an electrical component with live terminals — that's a technician's job, not a home one.
Fix it — step by step
- Cut the power and shut the inlet — before anything elseFor an electric heater: switch off its breaker at the panel (not just the on/off switch). For every type: shut the cold-water inlet valve feeding the heater. If there's no dedicated valve, shut the main stopcock for the property.If you can't identify its breaker, kill the main. And the water inside can be scalding — don't open any fitting until it has cooled.
- Dry everything and find exactly where it's leakingWipe the whole area dry, then lay dry kitchen paper underneath and at the fittings on top. Wait a while and watch: where does it wet first? The fittings on top? The safety valve on the side? The drain valve at the bottom? Or the tank body itself?Pinpointing the source is half the fix — it stops you from tightening a fitting when the real problem is the tank.
- If it's a loose fitting — tighten it gentlyIf the leak is at an inlet or outlet nut, hold it with an adjustable spanner and tighten a quarter-turn only. Don't overdo it — over-tightening cracks the nut or strips the thread. If it still weeps, undo it, wrap PTFE tape on the thread, and refit.Wrap the tape in the direction of the thread (clockwise as you look at the pipe end), 4-5 turns, pulled tight.
- Check the T&P valve and its discharge pipeIf the drip is from the safety valve: make sure the discharge pipe runs downward and is clear, not blocked. A light drip after heating can be normal expansion; a steady drip means the valve is fouled or faulty, or mains pressure is too high. Never plug the valve.If your water pressure is high (common with rooftop tanks and booster pumps), you may need a pressure-reducing valve on the supply — that fixes it at the root, and a plumber fits it.
- If it's the drain valve — tighten or replace itWith the tank empty and cold, try tightening the bottom drain valve a little. If it still weeps, replace it with a new one of the same size, using PTFE tape on the thread. Put a bucket under it, because whatever is left in the tank will come out.Never drain a hot tank while it's under pressure — shut the inlet, open a hot tap somewhere to break the vacuum, then work.
- If water is coming from the tank body — stop, the tank is finishedIf you find water weeping from the tank body or the seam weld (not from a fitting), that's internal rust and a pinhole. Stop here — no tightening, tape or sealant will fix it. The tank must be replaced; call a plumber.A tank-body leak grows suddenly and can rupture — if you find one, keep the power off and the water shut until the plumber arrives.
Tools & parts you'll need
When to call a professional
Call a licensed plumber if: water is weeping from the tank body itself or the seam weld (the tank must be replaced); the leak is at the heating element or thermostat (electrical work); the T&P valve is faulty and needs replacing; or the heater runs on gas — gas heaters are strictly a gas engineer's job. Never work on the heater while it's connected to power, or while it's full of hot water under pressure. If the breaker trips with the heater, or you get a slight shock off the hot tap, cut the power immediately and call a professional — the element may be pierced and the water live.
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Water is coming from the T&P valve — normal or a fault?
A brief drip right after the water heats can be normal thermal expansion. But a steady drip or a constant stream means either the valve is fouled/faulty or your water pressure is too high (common with booster pumps and rooftop tanks). Never plug the valve — it's the safety device that stops the tank exploding. Replace it, or fit a pressure-reducing valve, via a plumber.
There's water under the heater — how do I know if the tank is finished?
Dry everything, lay down dry paper, and watch where it wets first. If it's from a fitting on top or the drain valve at the bottom, it usually fixes with a tighten or a valve swap. But if water is weeping from the tank body itself or the seam weld, that's internal rust — the tank is finished and must be replaced, with no repair.
My rooftop solar tank is leaking — same advice?
Same principle but a bit more dangerous: the tank sits on the roof in the sun and its water can be scalding. Shut its inlet first, then check whether the leak is from the fittings (tightens) or the tank body (finished). Rooftop leaks are often at exposed fittings that the sun and heat degrade quickly. Working on a roof, sometimes with near-boiling water, may warrant a technician.
Mine is a gas or instant heater, not a tank — same steps?
No. Gas heaters and instant (tankless) heaters carry different hazards — gas leaks, combustion, carbon monoxide. Any water leak or gas smell from a gas heater means disconnect it and call a licensed gas engineer immediately. This guide is for electric and solar storage (tank) heaters.
Can I tighten the fitting while the heater is running to see if the leak stops?
No, never. Cut the power and shut the inlet before you touch any fitting, and let the water cool. The water inside can be hot enough to scald instantly, and the heater is on mains power. Work on it cold and disconnected, not while it's live.