Maintenance and descaling of electric water heater: how to extend its lifespan
Why maintenance of an electric water heater is more important than most people think
An electric water heater is one of those appliances most households don't even think about – as long as it works. It stands in the bathroom or utility room, doing its job quietly, while no one gives it a second thought. Until it stops heating, starts leaking, or your monthly electricity bill suddenly jumps by fifteen euros for no apparent reason. That's the problem: neglected maintenance doesn't show up immediately or dramatically, but slowly, through a hidden increase in costs and a shortened lifespan of the appliance.
We see the same scenarios over and over. A customer calls to say their water heater "won't even heat the bathtub," even though it's set to full power. When the technician arrives and opens the unit, they find the heating element covered in a layer of scale as thick as a finger – sometimes as much as 10 to 15 mm of hard deposits acting as insulation and preventing heat transfer to the water. Result: the heater draws the same amount of electricity as before, but the water is barely warm. Or, worse, the element overheats because the heat has nowhere to go and burns out. Replacing the element or the entire unit was really unnecessary – regular descaling would have prevented the whole situation for a fraction of the cost.
This article is a practical guide that will explain what happens inside your water heater, why limescale forms, how to descale it properly (and safely), and what else you can do to ensure your appliance serves you reliably for fifteen or twenty years instead of just five.
What happens inside a storage water heater
To understand where and why scale builds up, let's first look at how a storage water heater works. The tank is filled with cold water. An electric heating element (heating rod) submerged in the water is heated by the current and transfers heat to the surrounding water. A thermostat measures the temperature and turns the element on or off according to the set value. The water heats from the bottom, the warmer water rises to the top, and the cold water sinks to the bottom – natural convection occurs. Hot water is drawn from the top, while cold water flows in from the bottom.
The problem begins with the chemical composition of the water. Water in Slovak water supplies is usually moderately hard to hard – depending on the region, the hardness ranges from 10 to 40 °dH (German degrees of hardness). The water contains dissolved calcium and magnesium salts (bicarbonates). At room temperature, they remain in solution. When the water is heated above 60 °C, the balance is disrupted and these salts precipitate as solid calcium carbonate – limescale, CaCO₃. The highest temperature is directly on the surface of the heating element, so scale builds up there primarily. The harder the water and the higher the set temperature, the faster the deposits accumulate.
A layer of scale just 1 mm thick reduces heat transfer efficiency by about 7–10%. A layer 5 mm thick means a loss of up to 35% efficiency. This directly translates into longer heating times and higher electricity consumption. In the case of a flow-through heater, the situation is even more critical – its heating element operates with a much higher concentration of thermal power on a small surface, and if the flow is restricted by scale, the appliance may activate an overheat protection or simply shut off before the water is heated to the desired temperature.
Water hardness in Slovakia: where the problem is most pronounced
The situation is not the same everywhere in Slovakia. Bratislava and its surroundings, parts of the Záhorie lowland, and southern areas of the Nitra region are regions with very hard water, where scale builds up quickly. Banska Bystrica, parts of central Slovakia, and mountainous areas have softer water, where the descaling interval is longer. If you're unsure, call your local water utility or use simple test strips available at pharmacies and pool chemical stores.
Approximate table of recommended descaling intervals based on water hardness:
| Water hardness | Value (°dH) | Descale interval | Note |
|---|---|---|---|
| Soft | 0–7 °dH | every 3–4 years | e.g. mountainous areas |
| Moderately hard | 8–14 °dH | every 1.5–2 years | most urban areas |
| Hard | 15–21 °dH | every 12 months | Bratislava, Nitra, Trnava |
| Very hard | over 21 °dH | every 6–8 months | some southern areas |
Storage vs. flow-through heater: different sensitivity to scale
Storage and flow-through heaters are affected by limescale differently in intensity and location. It's important to understand this, as the maintenance procedure varies.
Storage heater – for example, electric storage water heater BD 2.0 kW 30 l top-mounted – heats water gradually and keeps it in a tank. The temperature of the heating element is lower, so scale builds up more slowly. On the other hand, the tank holds a larger volume of water that needs to be heated, and the interior of the tank is difficult to access for maintenance. In addition to the element, scale also accumulates at the bottom of the tank as a solid sediment. A storage heater also contains a magnesium anode (sacrificial anode), which actively protects the tank from corrosion and is consumed over time – its replacement is a separate part of the maintenance process.
Flow heater – such as the electric flow water heater MK1 3.5 kW or MK1 4.5 kW – heats water instantly during flow. The heating element operates at a higher power and its surface temperature is higher. Limescale forms more intensively and quickly. In addition, the internal channel of the heater has a small diameter – even a thin layer of limescale can significantly narrow it and restrict the flow, which triggers the appliance's safety shutdown. With flow heaters operating under no pressure (for example, PM 3.5 kW or PM 4.5 kW), it is also important to regularly clean the nozzle or outlet cover, where limescale can visibly deposit from the outside.
Step by step: how to descale a storage water heater
Before you start anything, read the instructions provided with your heater. Each manufacturer has its own recommendations and warranty conditions – some tasks require a professional, while others can be done by a handy homeowner. Here we describe a procedure that applies to most common storage heaters.
What you will need:
- Descaling agent (citric acid or a special descaler for water heaters – acetic acid is too aggressive for seals)
- Wrenches (spanner, possibly a socket wrench for the heating element)
- Bucket and hose
- Sealing ring for the heating element (we recommend replacing it every time you remove the element)
- Flashlight
- Protective gloves and goggles
Descaling procedure for a storage water heater
1. Turn off and cool down. Always start by disconnecting the heater from the power supply – it is not enough to just turn off the thermostat, you must unplug the appliance or switch off the circuit breaker. Then let the water cool down for at least 2–3 hours. Never work with hot water – the risk of burns is real and serious.
2. Drain the tank. Close the cold water supply to the heater (ball valve on the inlet). Open a hot water tap somewhere in the house to equalize the pressure. Then open the drain valve or connect a hose to the drain valve and drain the entire tank. If your heater does not have a drain valve, you will need to loosen the bottom inlet – a bucket is essential in this case.
3. Remove the heating element. The heating element is usually fastened to the side or bottom of the tank with a large nut. Loosen it with a wrench and carefully remove the element. It will likely be accompanied by the remaining water and sediment from the bottom – do this over a bucket. Discard the old sealing ring and replace it with a new one.
4. Mechanical cleaning. Carefully remove the thick layer of limescale from the element using a plastic (not metal!) scouring pad or a special scraper. Limescale is brittle and most of it will fall off on its own. Never saw or cut – you might damage the surface of the element.
5. Chemical descaling. Prepare a solution of citric acid in a ratio of approximately 100 g of powder per liter of water (or according to the instructions of the chosen product). Place the element into a container with this solution and let it work for 2–4 hours. You will see the limescale cracking and falling off. For the tank itself, the procedure is more complicated – partially fill the tank with descaling solution, let it work and then rinse thoroughly. Some modern heaters have a special descaling inlet – in such cases the procedure is easier.
6. Check the anode. While the element is out, don't forget to check the magnesium anode. It is a rod made of magnesium alloy that sacrifices itself for the tank – it reacts with corrosive substances instead of the steel of the tank. A standard anode has a diameter of about 26 mm and a length of 400–500 mm. If it is reduced to a diameter smaller than 10 mm or is crumbling, replace it. The lifespan of the anode depends on the water quality – in hard water it lasts 2–3 years, in softer water up to 5 years.
7. Reassembly and refilling. Install the element with a new sealing ring, tighten the nut (do not over-tighten – the seal might crack). Open the cold water supply and let the tank fill – before turning on the electricity, the tank must be full, otherwise the element will burn out immediately. Check the tightness of the connections. Then switch on the circuit breaker and let the heater run.
Descaling a flow water heater
A flow heater is descaled differently from a storage heater – it does not have a large tank, but a heat exchanger or a direct heating channel. The procedure depends on the construction of the specific model, so the manufacturer's instructions are even more important here. In general:
For most common flow heaters (e.g. pressure models MK1 4,5 kW), descaling is done using the so-called circulation method: disconnect the device from the power supply and water supply, connect hoses to the inlet and outlet ports leading to a common container with a descaling solution (citric acid, approx. 10 % solution). Using a small pump (or gravity), circulate the solution through the heater for 30–60 minutes, then rinse with clean water. This procedure is gentle on the seals and does not require disassembling the heating element.
For simpler models with an accessible heating element, you can proceed similarly to a storage heater – remove the coil and chemically descale it. For non-pressure models (such as PM 3,5 kW or PM 4,5 kW), do not forget to regularly clean the outlet cover and any possible inlet water filter.
Important note: never use strong acids (hydrochloric acid, sulfuric acid) for descaling water heaters – they would damage the seals, metals and plastics. Citric acid is safe and effective. Products labeled as "boiler descalers" from supermarkets usually contain exactly citric acid or its mixtures.
Magnesium anode: the quiet guardian of the tank's lifespan
We talk about the magnesium anode mainly in connection with storage heaters, because flow heaters usually do not have one (or have other protective measures). The anode is a rod made of a special magnesium alloy, inserted into the tank and electrochemically protecting the steel casing from corrosion. It works on the principle of a galvanic cell: magnesium is electrochemically "more active" than steel, so it reacts preferentially at the contact with water and the steel tank remains undamaged.
Problems arise when the anode is completely corroded – the magnesium is consumed and the tank is left without protection. Corrosion then proceeds rapidly and can lead to tank leakage, which means the end of the heater. Replacing the entire boiler due to neglecting a 10-euro anode is one of the most common unnecessary expenses we see in practice.
How to check the anode: During descaling, when you have the coil removed, most anodes are visible or accessible through a separate opening (depending on the model). The anode should have a diameter of at least 15–18 mm. If it is thinner, crumbling, or not visible at all (completely corroded), replace it immediately. Some anodes are integrated directly into the coil – in such cases, the entire component is replaced at once.
Note on water softeners: if you have a water softener (ion exchange) in your household, keep in mind that soft water is more aggressive for the magnesium anode – it wears out faster. Reduce the inspection interval to 12 months.
Other routine maintenance elements often neglected
Pressure relief valve and expansion tank
A pressure-type storage heater must be equipped with a pressure relief valve, which discharges excess pressure generated when heating water (hot water expands). The pressure relief valve is small, but a critically important safety component. Its capacity is usually set to 6–8 bar. If the pressure relief valve drips with every heating cycle, it may indicate that the expansion tank is missing or that the valve is clogged with scale and does not close properly.
Check the pressure relief valve manually once a year: pull the lever and check whether it releases water and closes again. If it does not release or remains open, the valve is likely calcified or damaged and needs to be replaced. The price of a new pressure relief valve is 5–15 euros – it is a cheap insurance against a bursting tank.
Water inlet filter
If your house has a network filter (so-called "kolin" filter or mechanical filter on the water supply), regularly replacing or rinsing its insert is also part of heater maintenance. Dirt from the filter can get into the device and settle inside. This is especially true for flow heaters, where the internal channels are narrow.
Temperature setting
Many people set the thermostat of a storage heater to maximum (70–75 °C) under the belief that "more is better". In reality, this unnecessarily accelerates scale formation. The recommended operating temperature is 55–60 °C – this temperature is sufficient to eliminate the bacterium Legionella pneumophila (dies at temperatures above 55 °C), but does not produce scale as aggressively as 70 °C. If you want to regularly disinfect the heater, heat it to 70 °C once a month, but otherwise operate it at 55–60 °C.
Checking the bottom of the tank
Water scale sediment settles at the bottom of the tank and accumulates there for years. Regularly draining a portion of water (about 5 liters) through the drain cock can remove this sediment before it hardens and starts making noise during heating (characteristic cracking and breaking). We recommend doing this every 3–4 months.
How to Prevent Limescale: Preventive Measures
Descaling is a reaction to a problem that has already occurred. Much more effective is to prevent limescale formation in the first place. There are several proven methods:
Water softener: An ion-exchange water softener removes calcium and magnesium ions from water by replacing them with sodium ions. Softened water practically does not form limescale. The disadvantage is a higher initial cost (a central water softener for the whole house costs 500–2,000 EUR including installation) and regular regeneration with salt. It is not suitable for every household – people with heart or circulatory diseases should be careful about the increased sodium content in the water.
Magnetic or electronic water conditioners: These devices (so-called water magnets or ANTICAL devices) change the physical structure of the salts so that limescale does not adhere firmly to surfaces. Their effectiveness is questionable and not fully scientifically proven, but in practice, many customers observe a positive effect at least for common water hardness levels. The price is low (20–80 EUR), and installation is simple.
Polyphosphate doser: Adds a small amount of polyphosphates to the water, which bind calcium ions and prevent their precipitation. It is cheap and simple, but it adds chemicals to the water – it is not suitable for drinking water without further treatment. It works well for water heaters.
Reducing heating temperature: As we have mentioned, operating at 55–60 °C instead of 70–75 °C significantly slows down limescale formation. This is the cheapest and simplest preventive step.
Signs that the water heater needs descaling or repair
The water heater will let you know when something is wrong. Do not ignore the following symptoms:
- Longer heating time: A tank that used to heat water in an hour now takes an hour and a half – a classic sign of a limescale-covered heating element.
- Cracking and rumbling: A noisy water heater is not just annoying. Cracking is the sound of limescale cracking under thermal stress, or sediment moving around the bottom of the tank. If you ignore it, the heating element can overheat.
- Higher electricity consumption: If you notice an increase on the electricity meter without any other change in consumption, the heater is using significantly more energy due to limescale.
- Water has a strange smell or taste: A smell of hydrogen sulfide (rotten eggs) may indicate problems with the anode or bacterial growth due to too low a heating temperature. Immediately increase the temperature and check the appliance.
- Leaking safety valve: The valve drips with every heating cycle – the expansion tank is missing or the valve is clogged.
- Weak pressure of hot water: In a tankless heater, the cause may be a clogged inlet filter or narrowing of the channels due to limescale.
- Heater turns off before reaching temperature: In a tankless heater, this may be a sign of overheating protection being activated due to reduced flow.
More information on common faults and their solutions can be found in the article Common faults of electric water heaters and how to fix them in this Knowledge Center.
When to call a professional and when you can handle it yourself
Regular visual inspection, draining sediment from the drain valve, and checking the safety valve are tasks that every handy homeowner can perform without any expertise. Descaling the heating element with its disassembly and replacing the anode are a bit more demanding – they require basic tool skills and knowledge of the procedure. Usually, even a layperson can handle them if they follow the procedure and are not in a rush.
We recommend calling a professional (a heating technician or electrician) in these situations:
- The heater is under warranty and you do not want to lose the warranty by repairing it yourself
- You cannot loosen the heating element (it is seized by limescale) and there is a risk of thread damage
- You see corrosion on the tank or water leaks
- The electrical installation of the heater does not look in order (burned terminals, cracked cables)
- The heater is installed in a hard-to-reach location (e.g., in a hidden niche or too high up)
If you are deciding whether to repair or replace the heater, consult a technician: if the tank is rusted, the anode is long gone, and the appliance is more than 12 years old, it usually does not pay to invest in it. New models are more energy-efficient and will save you on operation costs.
Most frequently asked questions (FAQ)
How often should an electric water heater be descaled?
It mainly depends on the water hardness in your area. For soft water (under 7 °dH), descaling every 3–4 years is sufficient. For moderately hard water (8–14 °dH), every 1.5–2 years. For hard water (15–21 °dH), typical for Bratislava, Nitra, or Trnava, we recommend descaling once a year. For very hard water above 21 °dH, the interval is even shorter – every 6–8 months. If you are unsure about the water hardness, call your local water utility or use test strips.
What to use for descaling – citric acid or a commercial descaling product?
Both approaches are correct and effective. Citric acid is cheap, available, and safe for heater materials. A commercial product (from a pharmacy or chemical store) is more convenient – it has the correct dosage and, since it is specifically formulated for this application, it eliminates the risk of an overly strong solution. Never use concentrated hydrochloric acid (HCl) or pure acetic acid – they aggressively damage seals and metal parts. Acetic acid is acceptable in the form of food-grade vinegar (9 %), but citric acid is more reliable.
Can I turn on the heater if there is a descaling solution in the tank?
No, under no circumstances. Heating the descaling solution could release aggressive vapors, damage seals, and in the worst case cause corrosion damage to the tank. Descaling is always done cold and without electrical power. After descaling, thorough rinsing with clean water is essential – at least 2–3 times the tank volume.
The heater clicks and cracks during heating – is it dangerous?
Clicking and rumbling of a storage heater is usually not immediately dangerous, but it is a clear sign that limescale or sediment has built up inside. Limescale cracks under thermal stress, and sediment at the bottom moves and hits the walls. Long-term neglect of this condition leads to overheating of the heating element (surface temperature rises because limescale prevents heat transfer to the water), which shortens its lifespan and increases energy consumption. We recommend descaling as soon as possible – at the latest within a few weeks of noticing these symptoms.
I forgot about the anode – what happens if it is consumed?
When the magnesium anode is completely consumed, the steel tank of the heater is left without electrochemical protection. Corrosion that was previously "absorbed" by the anode will now attack the tank walls directly. With hard water, corrosion can appear within 1–2 years after the anode is consumed. The result is rust or a hole in the tank – the heater can then only be replaced, not repaired. Always check the anode during descaling and replace it while there is still time – it costs only a fraction of a new heater.
The tankless heater does not heat the water sufficiently – can limescale be the cause?
Yes, it is one of the most common causes. Limescale in a tankless heater does two things: it narrows the internal channel (reducing flow, which can trigger a safety shutdown), and at the same time it insulates the heating element from the water (heat is not transferred efficiently). The result is lukewarm water despite full power. Descaling using the circulation method usually resolves the issue. If the problem persists after descaling, it may be another fault – more about this in the article Common faults of electric water heaters and how to fix them. If you are considering what power of a tankless heater you need, the article What power of a tankless water heater do I need: 3.5 kW, 4.5 kW or 5.5 kW? will help you.
Conclusion: a little regular care will save you a lot of money
An electric water heater is a robust and reliable appliance that can easily last 15–20 years with proper care. Without it, its lifespan is reduced by half or even more, and in its final years it will cost you significantly more in electricity. The key principles are simple: regularly descale according to water hardness, check and replace the magnesium anode, inspect the safety valve once a year, periodically drain sediment from the bottom, and set the temperature to a reasonable level of 55–60 °C.
You can perform most of these tasks yourself, and the entire annual maintenance will cost you no more than 20–30 euros for materials (citric acid, gasket, possibly an anode). This is significantly less than a new water heater or unnecessarily high electricity bills that a limescale-covered appliance gradually leads to. If you are considering a new appliance or trying to decide between a storage and a tankless model, the article How to choose an electric water heater: storage or tankless? or the topic Pressure vs. non-pressure water heater: what is the difference and which to choose? in this Knowledge Center will help you.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your household? Write to us – we are happy to help.