Electric water heater not producing hot water: element, thermostat or limescale

Short answer: if an electric water heater no longer gives hot water, it is usually the heating element or the safety thermostat. First check whether the circuit in the fuse box is still on. An element costs between €100 and €220. If the hot water runs out sooner and sooner, the tank is scaled up or the anode is spent.

How an electric water heater works

Inside the tank is a heating element that heats the water to the set temperature, usually between 60 and 70 degrees. A control thermostat switches the element on and off; above that sits a high-limit or safety thermostat that shuts everything down if the temperature rises too high. The latter is a safety device that cuts out permanently when there is a problem and sometimes has to be reset by hand.

There is also a magnesium or titanium anode in the tank. It sacrifices itself to protect the steel against corrosion. More about this in our guide on replacing the anode.

No hot water: what to check

Start at the fuse box. A water heater often has its own circuit, and a tripped RCD is a common cause. If the RCD trips again as soon as you switch it on, switch the circuit off and call an installer: it points to an element leaking to earth, and that is exactly what the safety device is supposed to detect.

If the circuit is working, check whether the light or display on the water heater is on and whether the set temperature has not accidentally been set low. Some appliances have a holiday or eco mode that limits the output.

If the water stays cold while there is power, the safety thermostat comes into the picture. A.O. Smith reports this, for example, with code 0A5, main safety thermostat activated. Such a thermostat does not trip for no reason: the temperature was too high, and the question is why. Usually it is a control thermostat that no longer switches off.

What the parts cost

Part	Manufacturer number	Price
Inventum heating element 3 kW, 230 V	15100004	€ 105.95
Inventum heating element 230 V	S1204001	€ 122.95
Remeha electric heating element 2.7 kW, bent	95607758	€ 211.95
Remeha thermostat sensor for electric heating element	95861208	€ 86.95

All variants can be found under heating elements en thermostats and controls. With an element, pay attention to the output, the length, the thread size and whether it is bent or straight: together these four determine whether it fits.

Hot water running out sooner and sooner

This is a different problem from no hot water at all, and it is the most underestimated complaint. When limescale builds up on the element, it insulates it: the element gets hotter, the water heats up more slowly, and the element eventually burns out. At the same time limescale collects at the bottom of the tank, reducing the usable volume. You notice it because the shower runs cold sooner and sooner.

In hard water areas a water heater therefore needs descaling every few years, with the anode checked at the same time. That extends the life of the tank considerably and is much cheaper than a new appliance.

DIY or call an engineer?

A water heater combines water and electricity, and that calls for care. Disconnect the power, close the water supply, drain the tank and only then remove the element. If you are familiar with both, you can do this yourself; if you are unsure about any of these steps, have it done. When refitting, make sure the gasket is seated properly: a leaking element quickly soaks the insulation.

If you are working on an indirectly heated cylinder connected to the boiler, the heating circuit is also involved and an installer is the logical choice.

Frequently asked questions

How long does a heating element last?

Eight to fifteen years, depending heavily on the water hardness and whether the tank is descaled. Limescale is the main wear factor.

Why does my RCD trip when the water heater switches on?

That almost always points to an element leaking current to earth, usually through a small crack in the sheath. Have it replaced and do not keep trying to switch the circuit back on.

Can I set a water heater higher to get hot water for longer?

That works, but above about 70 degrees limescale builds up faster and there is a risk of scalding at the tap. Around 60 degrees is a good balance, also with a view to legionella prevention.

Is repair still worthwhile on an old tank?

Replacing an element or thermostat is almost always worthwhile. If the tank itself leaks, that is the end of the story: a tank cannot be reliably repaired.