7 reasons why your electric water heater isn't heating (and how to fix it)

You turn on the hot water tap. You wait. And it comes out cold.

Or worse: the water comes out lukewarm for a few minutes and then it gets cold. The water heater seems to be working, but it's not heating the water properly . And then the questions arise: Is it broken? Do I need to replace it? How much will it cost to repair?

If you're searching for "electric water heater not heating" , "why my electric water heater stopped working" , "my electric water heater doesn't heat much" or "what to do if the electric water heater doesn't heat" , before thinking about buying a new one, there are several things you should check.

A scale-covered heating element, a faulty thermostat , a depleted magnesium anode , an electrical problem, a leaking safety valve , or even a water heater with insufficient capacity can all cause the same problem: running out of hot water when you need it most.

The good news is that not all of these problems mean you have to replace your water heater . Some can be easily detected and fixed with proper maintenance; others require a technician.

In this Termic guide, we show you the 7 most common reasons why an electric water heater isn't heating up , how to recognize each one, what you can check, and, above all, when you really need to repair or replace the unit .

Before opening any covers or handling any components, remember to turn off the power. If you are not experienced with electrical installations, do not risk your safety: some diagnostics must be performed by certified technicians.

🔍 First: What to check before touching anything?

Before any diagnosis, there are three safety checks you should never skip:

1. Turn off the electricity before opening any cover or panel of the water heater.

2. Make sure the water heater is full of water. If the tank is empty and the heating element turns on, it will burn out in seconds (this is called "dry running" and is the number one cause of irreparable damage).

3. Do not handle electrical components if you lack experience. If your diagnostic task involves testing continuity with a multimeter or opening the thermostat cover, and you are unsure how to do so, call an SEC-certified technician.

That said, these are the 7 problems we encounter most frequently:

1. The heating element is covered in limescale (the most common cause).

The heating element is the component made of a highly durable metal alloy responsible for heating the water.

Symptom: The water gets a little warm but never quite warm enough. The water heater makes noises (like boiling water). You hear the thermostat turning on and off more often than usual.

What's happening: The heating element is the "heart" of the water heater. If you live in an area with hard water (like much of Santiago, Antofagasta, or Arica), limescale builds up on the element, forming an insulating layer. This layer prevents heat from being transferred to the water. The element continues to consume electricity, but the heat doesn't reach where it needs to.

How to verify it:

On most Termic water heaters, you can access the heating element by removing the bottom access panel. If you see a whitish or brownish coating on it, that's the problem.

Solution:

Descaling: Mix Kalklöser P (or any anti-scale descaling agent for heating equipment) with warm water in a 1:10 ratio. Immerse the heating element until the calcium loosens [see Termic maintenance article].

Prevention: The heating element should be checked every 1-2 years depending on the water quality. Using a mixing valve helps reduce the water temperature and, consequently, limescale buildup.

💡 Termic Fact: Termic water heater heating elements are coated with vitreous enamel ceramic and Incoloy alloy, which reduces limescale buildup. But even the best heating element needs regular maintenance.

2. The thermostat is out of calibration or defective.

The thermostat in an electric water heater is the device responsible for measuring and regulating the water temperature inside the tank. Symptom: The water comes out too cold (or too hot). The indicator light on the water heater is working, but the water doesn't reach the set temperature.

What's happening: The thermostat is the "brain" that decides when to turn the heating element on and off. If it's out of calibration, it might be cutting off the heating too soon. If it's faulty, it might not send the signal to turn on at all.

How to verify it:

Check the knob or digital control: is it set to the correct temperature? Sometimes the problem is as simple as someone accidentally turning it.

If the water heater has a red pilot light and it is not on, but there is no hot water either, the thermostat may be cutting off the power supply.

Solution: If it's out of calibration, it can be adjusted following the equipment manual. If it's defective, it needs to be replaced. Do not attempt to repair a thermostat: it's a safety device.

3. The sacrificial anode is depleted (the "guardian" of your thermos)

The magnesium anode is an anti-corrosion protection bar that wears down to protect the water heater tank.

Symptom: The water comes out with a metallic or rusty smell. The hot water turns brown. In advanced cases, you start to notice that the heating element corrodes faster than normal.

What happens: The magnesium anode is a rod located inside the pond that "sacrifices" itself by oxidizing before the steel of the pond [see article "How to choose solar ponds"]. It's the cheapest part of the system and the most important for your pond to last 25 years instead of 5.

If the anode fails, the tank is left unprotected and begins to corrode from the inside. The water acquires a metallic taste and smell.

How to verify it:

Access is through the access cover. The new anode is 20 mm in diameter. If it is less than 12 mm, it must be replaced immediately [see Termic maintenance article].

Solution: Replace the anode. It's an inexpensive part and the replacement is quick. If you wait too long, the tank can rust, and then there's no solution: you'd have to replace the entire water heater.

4. The water heater is not receiving enough electricity (check this first)

A typical electric water heater requires between 1,500 and 2,500 W of power and consumes between 2 and 4.5 kWh per heating cycle, depending on its capacity (liters) and daily usage. Based on this, we can see the following:

Symptom: The water heater does not turn on at all. The pilot light is off. There is no heating noise.

What's going on: Before assuming the thermos is faulty, check the obvious:

Is the plug properly connected?

Is the circuit breaker in the electrical panel tripped?

Has the residual current device (30 mA) not tripped?

How to verify it:

Try plugging another appliance into the same outlet. If it works, the problem is with the water heater. If not, it's with the electrical circuit.

Solution: If the circuit breaker trips repeatedly, don't force it. A breaker that trips repeatedly indicates an internal short circuit or a broken resistor. In that case, the problem is electrical and requires a technician.

5. The safety valve is leaking (and you're losing hot water)

The safety valve of an electric water heater is a mandatory component that protects the appliance and your home: it releases excess internal pressure when the water heats up and expands, preventing serious leaks, damage to the tank, or even an explosion.

Symptom: Water is constantly dripping from the safety valve. The water heater seems to be working, but the hot water runs out sooner than expected.

What's happening: The safety valve is a mandatory component that releases pressure when the water expands due to heat. An occasional drip is normal. But if it drips constantly, it could be because:

The water mains pressure is too high (over 5 bar).

The valve is clogged with limescale or sediment.

The thermostat is overheating the water and activating the valve as a safety mechanism.

How to verify it:

Manually operate the valve lever. If it does not move or is stuck, it needs cleaning or replacement.

Solution: Clean or replace the valve. If the mains pressure is very high, installing a pressure regulator is recommended.

6. The water comes out hot but runs out very quickly

The water comes out hot, but after a few minutes it cools down. The thermos seems to be working, but "it doesn't last or it's not enough."

What's happening: This isn't a problem with the water heater. It's an issue with the capacity being incorrectly sized.

Check the capacity of your thermos:

50-80 liters: Ideal for 1-2 people.

100-120 liters: Recommended for 2-3 people.

150 liters: For 3-4 people.

If there are four people in your household and you have an 80-liter water heater, it simply won't be enough. It's not that the water heater is faulty; it's just too small for your needs.

Solution: If capacity is insufficient, consider:

Install a timer so that the water heater heats up at strategic times.

Raise the thermostat temperature (to 60-65°C, without exceeding 75°C).

If the demand is much higher, consider a higher capacity thermos.

Did you run out of capacity in your thermos?

At Termic we have electric water heaters of 50, 80, 100, 120 and 150 liters, all with a vitreous enamelled steel tank, magnesium anode and Incoloy 840 heating element. Designed for the water and pressure conditions of Chile, with a 2-year warranty.

Tell us about your situation and we'll recommend the exact thermos you need, without overpaying or falling short.

7. There is an internal leak (the most serious cause)

Symptom: The water heater is leaking from the bottom. There are rust stains on the floor. The water comes out with particles.

What's happening: The inner tank has been perforated by corrosion. This occurs when the sacrificial anode has been depleted for a long time and no one has replaced it.

How to verify it:

Visually inspect the bottom of the water heater. If there is moisture or dripping that is not coming from the connections, the tank is compromised.

Solution: A punctured tank cannot be repaired. The only solution is to replace the water heater. That's why it's so important to check the anode every 6-12 months.

🔧 When should I call a technician?

Call an SEC-authorized technician when:

1. The breaker trips repeatedly after being reset.

2. There is a burning smell or sparks coming from the electrical connections.

3. The tank is perforated (dripping from the body of the thermos).

4. You don't feel safe opening the manhole covers.

💡 Prevention: the best "remedy" is maintenance

Most of the problems in this guide can be prevented with regular maintenance:

Every 6-12 months: Visual inspection, safety valve test, anode verification.

Every 1-2 years: Descaling of the heating element (depends on the water hardness).

Every 2 years: Complete maintenance by an authorized technician.

A well-maintained Termic water heater can last 10-25 years depending on the model. Without maintenance, the same unit could fail in 5-7 years. The difference lies in the care.

📞 Do you have questions about your electric water heater?

At Termic, we specialize in electric water heaters and solar thermal systems designed for Chile's water conditions and pressures. If, after reviewing this guide, you still don't know what's wrong with your unit, please contact us.

We'll help you diagnose your problem with no obligation. And if you need a spare part or a technician, we'll guide you.