Vaillant electric heating coil 2/4/6 kW for 300-500 l tanks

Product detailed description

Vaillant electric heating element 2/4/6 kW for 300 – 500 l cylinders

This electric heating element is an optional accessory for Vaillant large-volume hot water cylinders of the uniSTOR VIH R 300/400/500 and auroSTOR VIH S 300/400/500 series, which are factory-prepared for its installation via a G1½" flange connection on the top or side of the tank. Installing this element converts an originally purely indirect-heated cylinder (dependent solely on heat from a boiler or heat pump) into a hybrid device that can also heat domestic hot water directly by electricity, independently of the main heat source. The output of the element can be switched between three levels – 2, 4 or 6 kW – according to current needs and the capacity available from the home's electrical connection.

The most common reason for adding this element is the ability to completely shut down the heating boiler during the summer months, when its only purpose is domestic hot water preparation – in such a case, the hot water is heated exclusively by electricity, which can be advantageous, for example, with solid fuel boilers (where it would be impractical to fire up the boiler in summer just for DHW), or simply as a backup heat source in case of shutdown, servicing or failure of the main heat source. This element is also frequently added to cylinders that are primarily connected to a heat pump in a bivalent configuration, where it serves as an additional source during periods of extreme frost, when the heat pump's output drops and an additional (bivalent) heat source is needed.

Technical characteristics

How the electric heating element works

The electric heating element is inserted directly into the interior of the cylinder through a mounting flange with an external G1½" thread, which is fitted into a prepared socket on the tank shell. The element is immersed directly in the water inside the cylinder and works on the principle of classic electric resistance heating – similar to the heating element in a common electric water heater, but integrated into an already existing indirect-heated cylinder. The built-in adjustable thermostat maintains the set water temperature, and the safety temperature limiter (STB – Sicherheitstemperaturbegrenzer) cuts off the power supply in case of thermostat failure and risk of overheating, thereby protecting the cylinder and the entire system from damage.

The choice of power level (2, 4 or 6 kW) depends on how quickly you need to heat up a given volume of water and how much power reserve your home's electrical grid has. Higher output means faster heating, but also a higher instantaneous load on the electrical grid and the main circuit breaker of the house – if there is insufficient reserve in the electrical connection (for example, when other high-power appliances are running simultaneously), it is recommended to choose a lower power level or consult an electrician about the sizing of the home's electrical installation.

Installation

Installation of the electric heating element must be carried out by a qualified electrician or service technician authorized to work on electrical equipment, as it requires connection to a separate electrical circuit with corresponding protection (circuit breaker) and possibly a residual current device, in accordance with applicable standards for electrical installations in areas with water. Before installing the element itself, a G1½" mounting flange must already be fitted in the cylinder (sold separately, see related product) – this flange is screwed into the prepared socket on the cylinder, and the cylinder must be drained of water before this operation. Once the flange is fitted, the body of the electric element is inserted and sealed into it, the electrical wiring is connected, and the desired temperature is set on the built-in thermostat.

Before first start-up, we recommend checking the functionality of the safety temperature limiter and the earthing of the entire system, as this is a device operating directly in a water environment under electrical voltage – incorrect installation or missing earthing poses a serious safety risk. After completing the installation, it is advisable to perform a trial run and verify that the thermostat correctly maintains the set temperature and that the safety limiter is correctly activated when the maximum temperature is reached, which we test by briefly setting the thermostat above the normal operating value (this procedure should be performed exclusively by an experienced technician).

Who is this accessory suitable for

• households with a solid fuel boiler who want to prepare hot water in summer without firing the boiler,
• households wanting a backup heat source in case of servicing, failure or shutdown of the main heat source,
• properties with intermittent heat supply from a central source (e.g. seasonal cottages, cabins),
• households planning to add photovoltaics in the future (in that case, however, we recommend considering directly the smart version with 0.5–3.5 kW regulation, which is better suited to work together with photovoltaics).

Difference from the smart (photovoltaic) version

This classic switchable version works simply as an on/off heating element with a fixed adjustable power level and thermostat – it has no communication with the photovoltaic inverter or with measurement of production surplus. If you plan to use surplus electricity from photovoltaics to heat water, the smart version with smoothly regulated output of 0.5 – 3.5 kW is more suitable, as it can respond to the currently available production surplus instead of a fixed power level. The classic version, on the other hand, is simpler, more reliable and cheaper where only simple manual or thermostatically controlled backup heating is sufficient.

Alternatives to electric backup heating

Besides the electric heating element, there are other ways to ensure independent summer heating of domestic hot water in a large-volume cylinder – for example, adding a small air-to-water heat pump designed directly for hot water heating, or (for auroSTOR models) adding solar collectors, which use solar energy instead of the electrical grid. Compared to these alternatives, the electric heating element is clearly the simplest and most affordable investment solution; however, in terms of operating costs per kWh of heat produced, it is generally not the cheapest long-term choice – its main advantage is simplicity of installation, low purchase price and the possibility of quickly adding it to an already existing cylinder without major construction work.

Safety and maintenance

The electric heating element immersed in water requires regular inspection of the thermostat and safety temperature limiter, ideally as part of the annual cylinder service. In areas with harder water, limescale may gradually build up on the surface of the element body, reducing heat transfer efficiency and extending heating time – in such a case, the element body should be inspected during servicing and mechanically cleaned if necessary. Before any handling of the element (replacement, servicing, cleaning), the power supply must be disconnected and the cylinder drained to prevent electric shock or scalding by hot water. We recommend entrusting these tasks exclusively to a qualified service technician, who will also check the condition of the flange seal and any signs of corrosion around the mounting socket, as well as the overall condition of the cylinder's magnesium anode, if the given model has one.

Why choose this accessory

Adding an electric heating element turns a Vaillant large-volume cylinder into a more versatile device capable of preparing hot water independently of the main heat source – an ideal solution for summer operation, backup in case of failure, or as an intermediate step before later adding photovoltaics. As this is original accessory directly from the cylinder manufacturer, full compatibility with the flange and dimensions of the cylinder socket is guaranteed, which cannot always be guaranteed with non-original universal replacements.

Operating scenarios and cost estimate

The operating costs of the electric heating element depend mainly on the current price of electricity, the cylinder volume, and the frequency of hot water consumption. In general, electric water heating is more expensive in terms of price per kWh than heating with a gas condensing boiler (especially at current energy price levels in Central Europe), so this element is usually not used as the main year-round heating method, but rather as a supplementary or backup solution – typically during the summer months with solid fuel boilers (where it is impractical to fire the boiler just for hot water), in case of failure or servicing of the main heat source, or in combination with photovoltaics, where it uses otherwise unused surplus of one's own electricity production instead of selling it cheaply to the grid.

For regular use, we also recommend considering time-switching of the element (for example using a separate timer switch or a smart socket) so that the backup heating is performed at times of a lower electricity rate, if your energy supplier allows this (dual-rate tariff, low tariff).

Compatible models in detail

The element is designed for a whole range of Vaillant large-volume cylinders with a G1½" flange connection – primarily the uniSTOR VIH R 300, VIH R 400 and VIH R 500 models (indirect-heated cylinders for stationary boilers), the geoSTOR VIH RW 300 (cylinder for heat pumps), and the auroSTOR VIH S 300, VIH S 400 and VIH S 500 (bivalent solar cylinders). Before ordering, we recommend verifying whether your specific cylinder model has a factory-prepared socket with a G1½" flange – for smaller models of the uniSTOR VIH R 120/150/200 series, this option is not available due to design reasons.

Package contents

The package includes the body of the electric heating element with a pre-selected or switchable power level, a built-in thermostat with a control knob or display (depending on the specific version), a safety temperature limiter, and a seal for fitting into the mounting flange. The mounting flange G1½" itself, electrical wiring, protection (circuit breaker, possibly a residual current device) and any timer switch are supplied and ordered separately.

Frequently Asked Questions