ATTACK Wall-mounted Horizontal Tank Z 125 OKCV - Right

Product detailed description

ATTACK Wall-mounted horizontal cylinder Z 125 OKCV - right is an indirectly heated domestic hot water (DHW) cylinder with a volume of 125 litres in a wall-mounted horizontal (OKCV) version with right-hand connection orientation. The cylinder is designed to be suspended above a suspended ceiling, in the space above a boiler, in a kitchen unit, or in another low-height space where a standard upright cylinder would not fit. Like other models of the Z series, it is an indirectly heated type - it has no heat source of its own; water is heated using the heating water from a connected ATTACK gas boiler via an internal heat exchanger.

The "right" connection orientation indicates on which side of the cylinder (viewed from the front) the water and heat exchanger inlets and outlets are located - this orientation must be chosen according to the layout of the pipework and space during installation, which is why the OKCV 125 model is manufactured in both versions (right and left).

Key features

• Inner tank made of steel sheet with a high-quality enamelled (glazed) surface resistant to corrosion and limescale build-up
• Magnesium protective anode against electrochemical corrosion of the tank - extends the cylinder's service life and is easily replaceable during a service inspection
• Hardened PUR foam thermal insulation wrapped in an outer jacket, which minimises heat loss while storing hot water
• Internal steel heating coil (heat exchanger) with a heat transfer area of 1.0 m² for indirect water heating from the boiler
• Suitable for connection to stationary ATTACK gas boilers (EKO COMBI, PLQ COMBI, KLQ COMBI, E COMBI, EZ COMBI series) as well as other heat sources with a properly sized heat exchanger
• Opening / socket for a thermometer or thermostatic sensor for heating control
• Outlet for an optional electric heating element (purchased separately) for water heating outside the heating season, when the boiler is not running
• Drain valve for easy draining and maintenance of the tank
• Robust construction with enamelling tested according to European standards for drinking water tanks
• Manufactured under the ATTACK brand - a proven Slovak manufacturer of heating technology

Type and version - right-hand orientation

The horizontal (OKCV) version is mounted suspended under the ceiling or in a suspended ceiling using hanging straps or a bracket (it is not designed to stand on the floor). This position is advantageous in spaces with low ceiling height, for example above a wall-mounted boiler, in a technical shaft, or in a kitchen unit.

The cylinder is manufactured in two mirror-image versions - right (R) and left (L) - depending on which side the cold/hot water and heat exchanger connections are located, viewed from the front of the cylinder. This particular product is in the right-hand version; if the project or existing pipework requires the opposite side, the mirrored left-hand version is also available (same 125 l volume, only the connection placement differs).

Before ordering, we recommend verifying the right/left version directly at the installation site according to the pipe routing, in order to avoid an unnecessary exchange.

Technical specification

Note: dimensions and weight are approximate estimates based on the volume and design type of the cylinder; exact values can be found in the manufacturer's technical data sheet or requested when ordering.

How indirect hot water heating works

The ATTACK Wall-mounted horizontal cylinder Z 125 OKCV - right is not a heat source itself - it has no burner or electric heating element of its own (the latter is only an optional accessory). The heating principle is as follows: heating water heated in the ATTACK gas boiler is pumped by a circulation pump to an internal steel heat exchanger (coil) submerged in the cylinder's tank. Through the wall of the heat exchanger, it transfers heat to the domestic water filling the internal volume of the 125-litre tank. The domestic and heating water never physically meet - they are separated by the wall of the heat exchanger, so there is no mixing or contamination of drinking water by the heating medium (which may contain corrosion inhibitors and other additives).

Heating control is provided by the boiler's control unit in cooperation with a temperature sensor (surface-mounted or immersed in the cylinder's socket) and usually a three-way switching valve, which redirects the flow of heating water from the radiator circuit to the cylinder's heat exchanger when DHW is required. This gives priority to hot water preparation over space heating, and the household has hot water available practically immediately after the circulation pump starts.

The advantage of this solution compared to instantaneous heating (a combi boiler without a cylinder) is that the cylinder stores a supply of already heated water - it is therefore possible to draw a larger amount of hot water at once (for example, filling a bathtub) without the output limitation that instantaneous heating in a boiler has.

How to choose the right cylinder for your boiler

When choosing the volume of a Z-series cylinder (100, 125 or 160 litres), it is recommended to base the decision primarily on the number of people in the household and hot water usage habits:

• 100 litres - suitable for 1-3 people, an apartment or smaller family house with standard consumption (showering, kitchen, bathroom without a tub or with occasional filling)
• 125 litres - suitable for 3-4 people, a typical family house, combination of shower and bathtub
• 160 litres - suitable for 4-5 or more people, households with higher demands for simultaneous draw-off (e.g. multiple bathrooms)

This particular ATTACK Wall-mounted horizontal cylinder Z 125 OKCV - right model has a volume of 125 litres with a heat transfer area of 1.0 m². The larger the heat transfer area, the faster the cylinder can "recharge" the hot water consumed at the same boiler output - when choosing between a standard and an "enlarged" heat exchanger (where both are manufactured, e.g. the OKC 125/160 series), also consider the output of your boiler: for boilers with higher output (25-30 kW), it is worth choosing the variant with a larger heat exchanger so that its output can actually be used for fast DHW heating as well.

The cylinder itself does not generate heat - it must be connected to a suitable source, usually a stationary ATTACK gas cast-iron boiler (EKO COMBI, PLQ COMBI, KLQ COMBI, E COMBI or EZ COMBI series), which has provision for connecting an external DHW cylinder via a three-way valve. These boilers prepare DHW only instantaneously or not at all, and it is precisely the external Z-series cylinder that adds the hot water storage function. When combined with a heat pump or solar system, we recommend choosing specialised HP or SOL series models (other products in our range), which have a heat exchanger sized for lower heat transfer medium temperatures.

Installation and connection

The horizontal cylinder is mounted suspended - most often on two or four suspension rods, brackets or straps anchored to the ceiling or supporting structure, or above a wall-mounted boiler in a common frame. Before installation, it is necessary to verify the load-bearing capacity of the ceiling/structure with regard to the weight of the filled cylinder (empty weight approx. 35 kg + the weight of 125 l of water, i.e. an additional approx. 125 kg).

The cold and hot water connections, as well as the heat exchanger circuit, are located on the side corresponding to the ordered orientation (right). We recommend installing shut-off valves on all connections, a safety valve on the cold water inlet (sized according to applicable standards), and, in the case of harder water, also a softening or dosing system to extend the tank's service life. Installation should be carried out by an authorised person (heating technician/plumber) in accordance with the manufacturer's installation manual and applicable legislation (in particular STN EN 12897 and related regulations for pressure vessels).

Maintenance and service

To ensure the longest possible service life of the ATTACK Wall-mounted horizontal cylinder Z 125 OKCV - right, we recommend following a regular service cycle:

• Checking the magnesium anode at least once a year (more often with harder water) - a worn anode must be replaced in time, otherwise it loses its protective function and corrosion of the tank from the inside accelerates
• Desludging/draining the tank via the drain valve once every 1-2 years, especially in areas with harder water, where limescale and sludge accumulate at the bottom of the tank
• Checking the safety valve on the cold water inlet - regularly turning it to verify its function and the patency of the drip pipe
• Checking the tightness of connections and the heat exchanger at each annual boiler service inspection
• In the case of hard water, consider installing a softening or dosing device, which significantly extends the service life of both the heat exchanger and the tank

Regular maintenance is also a condition for warranty acceptance in the event of a failure caused by corrosion or limescale deposits.

Safety, standards and legislation

The ATTACK Wall-mounted horizontal cylinder Z 125 OKCV - right is a pressure vessel that must be installed and operated in accordance with applicable technical standards and regulations, primarily STN EN 12897 (indirectly heated water heaters) and related pressure equipment regulations. A properly sized safety valve on the cold water inlet is always part of correct installation, protecting the tank against excessive overpressure during heating - its discharge/drip pipe must be routed freely into a space with a slope and must not be blocked or capped in any way.

We also recommend installing an expansion vessel on the cold water side (especially if there is a check valve or pressure reducing valve on the inlet that prevents backflow of water into the water supply network during heating and thermal expansion). Without an expansion vessel, the safety valve may open repeatedly, causing unnecessary water loss.

Always entrust installation, connection to the boiler's heating circuit, and initial commissioning to a qualified person authorised to install gas and heating equipment. Only professionally performed installation and a regular annual service inspection (together with the boiler inspection) are also a prerequisite for warranty acceptance in the event of a claim. The 125-litre cylinder is intended exclusively for heating drinking (domestic) water in the internal plumbing of buildings, not for other technological purposes.

Position in the ATTACK product range

The ATTACK Wall-mounted horizontal cylinder Z 125 OKCV - right belongs to the Z series - indirectly heated DHW cylinders of the ATTACK brand, which, in addition to this model, includes other volumes (100, 125, 160, 200 litres), versions (stationary OKH NTR/HV, wall-mounted OKC, horizontal wall-mounted OKCV) and special variants (e.g. with an additional 2.2 kW electric element built into the cylinder body, a solar SOL version with two heat exchangers, or an HP version designed for heat pumps). Thanks to the wide range of variants, it is possible to find a cylinder tailored exactly to the layout of the boiler room and the needs of the household.

We recommend combining this model primarily with stationary ATTACK gas cast-iron boilers of the EKO COMBI, PLQ COMBI, KLQ COMBI, E COMBI and EZ COMBI series, which have provision for connecting an external DHW cylinder, since the boiler itself does not contain a DHW cylinder.

Frequently asked questions

Do I still need a boiler for the 125 l cylinder, or does it work on its own?

The ATTACK Wall-mounted horizontal cylinder Z 125 OKCV - right is an indirectly heated type - it does not generate heat on its own. It must always be connected to a heat source, most often a stationary ATTACK gas boiler with provision for an external DHW cylinder (via a three-way valve), or to another suitable source with a sufficiently sized output.

Can the cylinder also be connected to a heat pump or solar collectors?

Yes, in principle it can, but we recommend rather the specialised HP series models (for heat pumps, with a large-area heat exchanger for a low-temperature source) or SOL (with an additional solar heat exchanger), which are directly sized for these sources. This Z-series model is primarily intended for a classic gas boiler.

How long does hot water stay hot in the cylinder without heating?

Thanks to the high-quality PUR insulation, standby losses are low, but the exact time depends on the room temperature and the difference relative to the water temperature. In general, under normal conditions the cylinder maintains a usable water temperature for roughly several hours up to overnight; for a longer idle period without the boiler running, it is advisable to add the optional electric heating element.

Is it possible to purchase electric heating additionally?

Yes, the cylinder has provision (a socket/outlet) for an electric heating element with a thermostat, which is purchased separately (for example, with an output of 2-6 kW depending on the model). This allows DHW heating even outside the heating season, when the boiler is shut down.

What is the warranty on the cylinder?

We provide a 5-year warranty on the insulated tank, and 24 months on other parts (e.g. anode, seals, accessories) from the date of dispatch, provided the installation conditions and regular maintenance (in particular anode inspection and replacement) are observed.

How often does the magnesium anode need to be replaced?

We recommend checking the anode at least once a year during the boiler service inspection. With more aggressive or harder water, more frequent checks and earlier replacement may be necessary - a worn anode loses its anti-corrosion function.

What is the difference between the 100, 125 and 160 litre volumes?

The difference lies mainly in capacity - a larger volume means more accumulated hot water available at once (e.g. when filling a bathtub while showering at the same time), but also larger physical dimensions and weight. The choice depends on the number of people in the household and water usage habits.

Why choose the horizontal OKCV version instead of an upright cylinder?

The horizontal (OKCV) version is suitable for spaces with low ceiling height, for example above a wall-mounted boiler, in a suspended ceiling, or in a kitchen unit, where an upright cylinder would not fit or would unnecessarily take up floor space.

What is the difference between the right and left versions?

The right/left designation indicates the side on which the water and heat exchanger connections are located, viewed from the front of the cylinder. The choice depends on the direction of existing or planned pipework - we therefore recommend verifying this side directly at the installation site before ordering.

Warranty and service

For ATTACK brand products, we provide a 5-year warranty on the insulated tank of the cylinder (provided that installation conditions and regular maintenance are observed, including inspection and replacement of the magnesium anode) and 24 months on other parts and accessories from the date of dispatch from the factory. Service and spare parts (e.g. anodes, seals, accessories) are available in Slovakia. If you have any questions about selection, installation or claims, please do not hesitate to contact us - we are also happy to help you choose a suitable boiler or controller for this cylinder.