Leaking water heater: where the water comes from and what to do now

First steps when the water heater leaks

If there is more than a few drops, first disconnect the heater from power — at the plug or the breaker in the fuse box. Water and electricity in the same place is a risk not to underestimate. If the socket or cable is wet itself, do not touch it; switch off the power at the fuse box instead.

Then close the cold water inlet valve to the heater. If there is no separate valve or it does not hold, close the main valve of the flat or house. No new water enters the tank and the leak slows or stops. The water inside is still hot, so be careful when touching connections.

• switch off power to the heater
• close the cold water inlet or main valve
• put a container underneath and dry the floor
• photograph the leak before taking anything apart
• in an apartment building, check the water is not reaching neighbours

A dripping safety valve is not always a fault

The most common “leak” we get called about is water from the safety valve. As water heats, it expands, and the valve releases the excess pressure. A few drops while heating are normal, which is exactly why the valve outlet should drain into the sewer.

It is a concern when the valve runs constantly, even when the heater is not heating, or when it never releases a single drop. In the first case limescale may stop the valve closing, or mains pressure is too high. In the second, the valve may have seized — which is worse for safety than dripping.

Plugging or capping the valve outlet is not a fix. The valve protects the heater, and blocking it can let excess pressure damage the tank.

Where water heater leaks usually start

To find the source, dry the heater and connections with paper and watch where a new damp spot appears. Water runs down the casing, so the puddle on the floor does not show where the leak began.

• cold and hot water connections and flexible hoses
• the safety valve and its threaded joint
• the flange gasket around the heating element (bottom, under the cover)
• a tap or pipework next to the heater
• the tank shell itself — usually on an old heater

Leak from a connection or hose

A leaking connection is good news: the tank is sound and the problem is fixable. The usual cause is an old seal, a worn flexible hose or a nut that has loosened over time. White or greenish deposits around a thread show water has been seeping there for a while.

Do not keep tightening flexible hoses — if a hose is rusty inside or its braid is damaged, it needs replacing. Over-tightening an old thread can ruin the joint completely.

Leak from the bottom: flange gasket or tank

If the heater leaks from the bottom, there are two main possibilities. The first is the flange gasket sealing the element to the tank. Limescale, heat and age make it hard. This kind of leak is often repairable: the tank is drained, the gasket replaced, and at the same time limescale is removed and the anode checked.

The second is corrosion through the tank shell. You see it when water comes through the casing or insulation rather than a joint, often rust-coloured. A tank wall cannot be reliably repaired — the only solution then is replacing the heater.

Opening the electrical cover is a job for an electrician or a qualified technician. Do not open it while the heater is connected to power or if water has reached the electrics.

Why water heaters start leaking

A leak usually comes down to age, limescale or pressure. The sacrificial anode protects the tank from corrosion; if it has not been replaced for years, corrosion starts eating the tank itself. Hard water leaves scale at the bottom, which overheats seals and speeds up wear.

High mains pressure strains both the valve and the connections. If the valve drips even when the heater is not heating, have the pressure checked — a pressure reducer may help. Poor installation, such as a missing valve or a pipe under tension, can also cause leaks.

Repair or replace

A leaking connection, hose, safety valve or flange gasket is usually repairable, and that makes sense even on an older heater if the tank is sound. A corroded-through tank means replacement regardless of age.

In between, the heater’s age and overall condition decide. If it is old, heavily scaled and the anode was never changed, each new repair may not last long. Then it is fair to discuss replacement too — not to sell, but to avoid the next water damage.

How to prevent water heater leaks

• have the anode checked at servicing and replaced if needed
• descale regularly in hard water areas
• check the safety valve works and its outlet is clear
• replace ageing flexible hoses before they leak
• check mains pressure if the valve drips constantly

When to call a plumber

Call a plumber if the leak does not stop after shutting off the water, if water comes from the bottom or the tank, if the valve runs constantly or if you cannot find the source. In an apartment building, where water can reach neighbours, do not wait. Santehnik24h comes out across Tallinn and Harju County, finds the cause of the leak and tells you honestly whether a repair makes sense or it is time to replace.