Frequently Asked Questions


What is the guarantee on an Ariston, Lemet, Wesen and Wijas product?

The Ariston has a 3 year guarantee on the tank and a 2 year guarantee on all other components.

Lemet has a 2 year guarantee on all components.

Wesen has a 5 year anti-corrosion guarantee on the tank and a 2 year guarantee on all other components.

Wijas has a 2 year guarantee.

In the description with each article you can check the guarantee period for your product.

If you have a malfunction it is important for us to first establish the cause. Once this has been determined we will send you the replacement part(s). Please contact us by email when you encounter a malfunction and supply us with photos so we can quickly ascertain the cause of the malfunction and whether this falls under the guarantee. Often you can solve the problem yourself, with a bit of help from us.

If you prefer you can also send the water heater back to us,so we can solve the problem for you in our workshop. We do not repair on-site as we do not have installers on the road. We do not install water heaters and cannot be held liable for installation or the dismantling of your water heater. But we shall do our utmost to assist you in solving your problem.

Please note that your guarantee will be void if you have not maintained the heater as indicated by the manufacturer or if you haven’t used the supplied safety relief valve. You can opt to use a KIWA or NSF approved safety relief valve. Always use a 6 bar for Lemet and an 8 bar for Wesen.  Never put an 8 bar safety relief valve on a 6 bar water heater or 6 bar safety relief valve on an 8 bar water heater!

Defects as a result of fluctuating water pressure are also not covered by the guarantee. Sometimes it is advisable to install a pressure reduction valve, on the water mains by the main valve, to protect your water heater from these fluctuations. Especially older buildings, farms and apartment buildings can suffer from fluctuating water pressure.

The guarantee applies exclusively on products supplied by us.

What is the function of the magnesium/ titanium anode?

The magnesium anode, also called electrical anode, limits the stress corrosion within the enamel tank, guaranteeing a longer life cycle of the electric water heater. The anode is also called a sacrificial anode and will corrode instead of the heating element. In other words it sacrifices itself to protect the heating element. An anode needs to be replaced every 2 to 2.5 years.

Some electric water heaters have a titanium anode instead of a magnesium anode. This is called a ACI system and works with a forced direct current voltage that is counter to the galvanized tension. This anode also needs to be replaced frequently.

What is the function of the pressure relief valve?

A water heater is a pressurized tank. When the heater operates the water inside the tank will expand. Once over the maximum tank operating pressure the pressure relief valve releases pressure from the tank by dripping water through a discharge pipe. This discharge pipe should always be installed directly underneath the pressure relief valve facing downwards to drain off the drops of expansion water into a drain.

Is the pressure relief valve you supply WRAS approved?

Yes it is. We supply a 6 bar WRAS approved pressure relief valve as standard with all LEMET water heaters. And an 8 bar WRAS approved pressure relief valve as standard with all WESEN water heaters. WRAS approved means the pressure relief valve complies with Water Supply (Water Fittings) Regulations for the UK and Scottish Byelaws.

Please make sure a discharge pipe (with or without a drain valve) is fitted directly underneath the pressure relief valve with0 a Tee fitting in between. The discharge pipe will drain off drops of expansion water coming from the pressure relief valve when the unit is operating. The discharge pipe should always be facing downwards to drain off uninterrupted in a drain. The pressure relief valve is there to reduce pressure and to prevent water from going back into the mains water supply line from the tank.

Please check this link for full details of a WRAS approval:

What is a WRAS approval?

Can you explain the function of the pressure relief valve and how water pressure works?

The water heater comes standard with a WRAS approved pressure relief valve with a maximum work pressure of 6 bar for Lemet and an 8 bar for Wesen water heaters. If you decide to use a different pressure relief valve valve and make sure it is the right bar and that it is WRAS approved. Using an incorrect pressure relief valve will result in damaging your water heater and will also void your warrantee. Never put an 8 bar pressure relief valve on a 6 bar water heater or 6 bar pressure relief valve on an 8 bar water heater!

Water pressure ensures there is sufficient water for all houses or apartments connected to the water network. Minimum water pressure required for a washing machine or central heating system is 1,5 bar. Ideal water pressure for a washing machine, dish washers and an electric water heater is around 3 bar. Anything over 5 bar will damage said household appliances.

If you live in an apartment, farm house, flat, old house or an elevated area you will most likely suffer from fluctuating water pressure and/or a too high water pressure. We highly recommend you to install a pressure reducing valve. Please install that valve where the mains water supply comes in the building and set it at 3 bar.

How does water pressure work in an apartment building?

With each meter gained in height, you will lose 0.1 bar in water pressure. To give an example in an apartment building:

  • first floor:   2,1 bar

  • second floor: 1,8 bar

  • third floor:    1,5 bar

  • fourth floor:    1,2 bar

A low water pressure will cause a reduced flow of water from your tap. First of all check if the tap is not the culprit. If the water pressure is too low please check main valve, of the water supply, to ensure that it is fully opened.

How much water does a shower use?

It depends on the shower head, the set temperature and the number of persons using the shower. Please use our water heater calculator: to find out what size water heater would probably suit your needs. It is just to help you on your way. In the end you decide what size you require. We always recommend, after using the calculator, to go for a slight overcapacity.

This calculator is based on a water temperature inside the tank of around 65 degrees celsius. You can enter the amount of people who want to shower, which shower head you use and how long each person normally showers.

To help you along here is a convenient chart of water consumption for various shower heads:

Water consumption per minute of your shower head

water-saving shower head

7 litres water per minute

Normal shower head

10-15 litres water per minute

Rain shower head

20- 25 litres water per minute

As you can see it is definitely worthwhile to consider a water-saving shower head as it saves at least 30% on water consumption. The patented shower head we offer has a very powerful jet of highly oxygenated water. See this link for full details: 

What is the maximum output of water (liters per minute)?

The maximum output of water, from your water heater, is dependant on several factors. The maximum water pressure depends on the pressure from the water network, as it is a closed system. The water pipe pressure is also influenced by the pipelines you are using. The water output also decreases as a result of narrow water pipes and by using lengthy pipeline (the longer the distance the water has to travel the less the output will be). The amount of water is thus also influenced by the width of the water inlet and outlet of the water heater. The standard water pipe diameter in the UK is ½” (15mm).

Guideline* for the maximum output of litres per minute is:

  • Diameter main water line 15mm (½”) - approximately 25 ltrs/min

  • Diameter main water line 22mm (3/4") - approximately 50 ltrs/min

  • Diameter main water line 28mm (  1 ") - approximately 75 ltrs/min

*This guideline is indicative.

What is the difference between a Wesen and an Ariston Velis?

  • The Wesen Inox Flat electric water heater looks very similar to the Ariston with its sleek and  modern design. But it is actually slightly slimmer than the Ariston Velis. The Wesen Inox Flat has a depth of 10.3”, The Wesen Silver has 9.48” and the Ariston Velis is 10.6”

  • The Ariston Velis shows the temperature per 10 degrees centigrade using LED’s. Wesen water heaters have a digital display allowing you to read the exact temperature.

  • The Ariston Velis EU boiler has a glass coated ceramic tank with an anode that needs to be replaced every 2 to 2.5  years. The Wesen has an Inox (stainless steel) tank making it corrosion free so you no longer need to replace the anode.

  • The maximum working pressure of the Wesen boiler tank is 8 bar. The 8 bar safety relief valve is always included.The Ariston Velis EU is tested up to 8 bar but is limited to a maximum working pressure of 7 bar. It also comes with a standard issued WRAS approved pressure relief (6 bar) valve.

  • The Ariston Velis EU has two separate heating elements (1000 watt and 1500 watt), which do not operate simultaneously. The Wesen Inox  has 2 heating elements. The Wesen Inox Flat has 1 double heating element in the first tank and one single in the second tank. The Wesen Silver Flat has 2 single heating elements. Activating the power button both elements will operate simultaneously, accelerating the heating process.

Inox Flat:

30 tot 50 litres, First tank: 2 x 700Watt / Second tank: 700Watt.

80 tot 100 litres, First tank: 2 x 800Watt / Second tank: 800Watt.

150 tot 200 litres, First tank: 2 x 1000Watt   / Second tank: 1000Watt

Silver Flat:

30 to 80 litres: First tank: 700 watt/ Second tank: 1300 watt.

  • Thanks to the Inox (Stainless steel) tank the Wesen water heater is much lighter than a Ariston Velis, making it easier to transport and to mount.

  • The Wesen water heater comes with the safety relief valve and the mounting screws are also included. With the Ariston Velis the safety relief valve is included but you will need to order a mounting set separately (do not forget to put this in your shopping cart during your ordering process).

Instant water heater: which instant water heater should I choose?

Please consult the following link:


What is the power consumption of an electric water heater?

The power consumption of an electric water heater is dependent on several factors. According to a Dutch government website power consumption is between £150 to £500 annually.

Here are the deciding factors to determine your consumption:

  • The size of your water heater in liters

  • Do you use a water-saving shower head or a rain shower? (see statistics below)

  • How often do you use warm water?

  • At what temperature do you use hot water?

  • How long do you use hot water for? (how long do you shower?)

  • What is the ambient temperature?

  • At what temperature is the water heater set?

  • What power does your electrical heater have?

Approximate water consumption per minute of your shower head

water-saving shower head

7 liters of water per minute

Normal shower head

10-15 liters of water per minute

Rain shower

20-25 liters  of water per minute

Can I put an electric water heater on an existing circuit?

Water heaters up to 150 liter can be fitted with a standard earthed plug and can be connected to an existing circuit on your circuit board. A standard fuse in the UK is 16A, which translates into 3600 watt.

Most water heaters have a heating element of between 1500 watt to 2000 watt, which translates to 6.5 to 8.7A. The 80 litre Wesen Inox Flat has the largest output of 2400 watt translating into 10.9A.

For water heaters of 200 liter or more we have two options:

  • The standard option of a single phase (230 vac) heating element

  • Or the power current option of 380Vac.
Can I install an electric water heater as replacement for a central heating boiler?

We wouldn’t recommend this as it will take a very long time to heat your living space. You would need to buy a very large electric heater that is capable of heating a substantial amount of water, which simply would not be economical compared to an ordinary gas-fired central heating boiler.

Moreover, the life expectancy of the anode and heating element would be much shorter as there is a lot of metals and other dirt in a closed central heating system that would corrode these parts very quickly.

You could use the electric water heater as a buffer tank and integrate it with an existing system, such as a wood fired boiler. These buffer tanks will not need a heating element or anode and instead of a glass coated enamel inner lining it will have to have a metal lining.

Can I connect an electric water heater to a gas-fired central heating boiler?

If you intend to fill the electric water heater with hot water from the central heating boiler, the answer is yes. This is called a hot fill and is possible with every single water heater we sell in our webshop. But we wouldn’t recommend it as it is a closed system with lots of dirt and other residu in the water. This will soon damage the water heater.

If you want to use hot water from the electric water heater to fill the central heating boiler please ask the supplier of your central heating boiler. Please mention to your supplier that it has to be suitable for hot fill.  

When choosing an electric central heating boiler, why do you specify square meters and not cubic meters?

The manufacturer has chosen to express the surface a unit can heat in square metres instead of cubic metres. That surface is based on a room height of no more than 7’9”(2.4 metres). Example: the 4kW model will heat a space of 50m2 with a height of 2.4 metres.

I use 1200m3 of gas per year. What would my energy costs roughly be if I would switch to an electric central heating boiler?

If you know what your gas consumption is per year you will have a rough indication, using the calculator below (we emphasize that this is a mere indication). Once you have switched to an electric unit you will not need gas any more. Also an electric unit is lower in maintenance compared to a gas-fired central heating boiler. In the calculator we have used 0,17 pence per kWh as the price for electricity. An average household uses roughly 1500m3 of gas annually.

Do I need a three-phase power supply for an electric central heating boiler?

Our electric central heating boilers can also be supplied as a 230 Vac version up to 9kW. You would of course require a separate circuit for the water heater on your circuit board. Please check the description of the product on our website for the necessary power supply and corresponding fuse.

Can I replace a gas-fired model for an electric central heating boiler?

Yes you can, but please make sure you use the supplied safety relief valve to retain the guarantee.

Please note that an electric central heating boiler is for heating your living space only, and not to produce hot water for shower and sink. For hot water you will need a separate electric water heater to supply hot water or instant water heater.

What capacity electric central heating boiler do I need to replace my gas-fired model?

A gas-fired central heating boiler normally has a higher capacity than an electrical model, as it also produces hot water for your shower and/or bath. In theory, the output you need to heat up your house with a gas-fired boiler is the same as it is with an electrical model. So if you require 9kW output with a gas-fired central heating boiler to heat up your house you would require roughly the same for an electric central heating boiler.  

Can the electric central heating boiler heat water?

No, it cannot. It can only heat your radiators and/or floor heating system.

What do I need to fit an electric central heating boiler?

Assuming you want to replace your gas-fired central heating boiler with an electrical model the first step is, obviously, to get rid of the gas-fired model and install the electrical model. Make sure you replace the existing valve with the supplied safety relief valve meant for the electric central heating boiler (ensuring optimal effectivity of your new boiler as well as to retain the guarantee).

If you are placing an electric central heating boiler in a new situation, where it does not replace an existing gas-fired model, bear in mind that you will need to order the radiators and/or floor heating system elsewhere as we do not supply any of these accessories.
Which electric central heating boiler should I choose?

Please note, that when you choose an electric central heating boiler you must bear in mind that it is strictly for heating the radiators or for your underfloor heating and NOT for providing hot water for a shower, a kitchen tap or a bath. Check for the entire range.  

Not every household will have sufficient power supply to install an electric central heating boiler. Always consult a certified electrician first to asses what is possible for your house. And to see what alterations in your circuit board need to be carried before purchasing an electric CV boiler.

You might find the following chart helpful in deciding what kWatt output you require to be able to heat your living space sufficiently. The manufacturers have chosen for square meters, based on a room height of no more than 7’9”(2.4 meters).  





4 kW ->

50 m2

12 kW ->

150 m2

6 kW ->

70 m2

18 kW ->

220 m2

9 kW ->

110 m2

24 kW ->

300 m2

What are the annual electricity costs of an electric central heating boiler?

It’s impossible to calculate. It depends on too many factors: the ambient temperature, set temperature, the temperature of the water etc.

In practice an electric central heating boiler will not differ much from a gas-fired heating boiler.
What is the power consumption of an electric central heating boiler and an instant water heater?

Assuming you have an electric central heating boiler or instant water heater of 9kW it goes without saying that it will consume 9kW. How often it has to heat up all depends on the set temperature, ambient temperature, temperature of the water etc. And that will determine your total consumption.

What is a heat pump boiler?
A heat pump boiler takes air in through a ventilation system and extracts ambient heat from that air to heat the water. The air drawn in is channelled through a heat exchanger that is filled with a coolant that produces a gas. The created gas is sucked in by a compressor creating a higher temperature. That heated gas is then sent through a second heat exchanger creating more heat. The heat with the addition of electrical energy leads to a desired temperature that helps produce hot water. This process repeats itself to adhere to your hot water request.  

Compared to a conventional electric water heater a heat pump boiler uses up to 3 times less energy. A heat pump boiler will only be economically interesting when you use more than 100 litres of warm water a day. It goes without saying that the more warm water you consume per day, the more interesting the option of installing a heat pump boiler, becomes.
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