ATTACK OKC 125/1m2 Wall-Mounted Storage Tank

Product detailed description

ATTACK Wall-Mounted Cylinder OKC 125/1m2 is an indirectly heated wall-hung domestic hot water (DHW) cylinder with a capacity of 125 litres and an enlarged heat exchange surface of 1 m², designed to be mounted on the wall next to a wall-hung or floor-standing ATTACK gas boiler. The cylinder does not have its own heat source - water inside it is heated indirectly by heating water from the boiler, which circulates through the internal steel heat exchanger.

The wall-hung OKC design saves floor space in the boiler room or utility room, as the cylinder is hung on the wall on the same bracket or next to the boiler. It is therefore a suitable choice especially for apartments, smaller houses and rooms where there is not enough space for a floor-standing (free-standing) cylinder.

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 minimizes heat losses during hot water storage
• Internal steel heating coil (exchanger) with a heat exchange surface of 1.0 m² for indirect heating of water from the boiler
• Suitable for connection to floor-standing ATTACK gas boilers (EKO COMBI, PLQ COMBI, KLQ COMBI, E COMBI, EZ COMBI series) as well as to other heat sources with a correctly sized exchanger
• Opening / pocket for a thermometer or thermostatic sensor to control heating
• Outlet for an optional electric heating element (purchased separately) for additional 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 design

The model designated 125/1m² is equipped with an enlarged heat exchange surface of approximately 1 m² (at a volume of 125 l), which in practice means faster water heating start-up and higher peak hot water draw-off performance (e.g. simultaneous bath filling and showering) compared to the basic Z 125 OKC version with a standard exchanger. It is therefore particularly suitable for households with higher DHW consumption or with a higher-output boiler that can effectively utilize this larger exchanger.

Structurally, it is a wall-hung (wall-mounted) cylinder - it is mounted on the wall using a supplied or separately sold wall bracket, usually in close proximity to the boiler so that connecting pipes are as short as possible.

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 Cylinder OKC 125/1m2 is not a heat source itself - it has no burner or electric heating element of its own (this is only an optional accessory). The heating principle is as follows: heating water heated in the ATTACK gas boiler flows via a circulation pump into the internal steel heat exchanger (coil) immersed in the cylinder's tank. Through the exchanger wall, it transfers heat to the domestic water, which fills the internal volume of the 125-litre tank. The domestic and heating water never physically meet - they are separated by the exchanger wall, 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 managed by the boiler's regulation in cooperation with a temperature sensor (surface-mounted or immersed in the cylinder's pocket) and usually a three-way diverter valve, which, upon a DHW demand, redirects the flow of heating water from the radiator circuit to the cylinder's exchanger. This gives hot water preparation priority 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 off a larger amount of hot water at once (for example, filling a bathtub) without the power limitation that instantaneous heating in a boiler has.

How to choose the right cylinder for your boiler

When choosing the volume of a cylinder from the Z series (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 bathtub or with occasional filling)
• 125 litres - suitable for 3-4 people, a typical family house, a combination of shower and bathtub
• 160 litres - suitable for 4-5 or more people, households with higher demand for simultaneous draw-off (e.g. multiple bathrooms)

This particular model, the ATTACK Wall-Mounted Cylinder OKC 125/1m2, has a volume of 125 litres with a heat exchange surface of 1.0 m². The larger the heat exchange surface, the faster the cylinder can "recharge" the hot water consumed at the same boiler output - when choosing between a standard and an "enlarged" exchanger (where both are manufactured, e.g. the OKC 125/160 series), also consider your boiler's output: for boilers with higher output (25-30 kW), it is worth choosing the variant with a larger exchanger so that its output can actually be utilized for fast DHW heating.

The cylinder itself does not produce heat - it must be connected to a suitable source, usually a floor-standing 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 only prepare DHW instantaneously or not at all, and it is precisely the external cylinder of the Z series that adds hot water storage capability. When combined with a heat pump or solar system, we recommend choosing specialized models from the HP or SOL series (other products in our range), which have an exchanger sized for lower heat carrier temperatures.

Installation and connection

The wall-hung cylinder is mounted on a load-bearing wall using a supplied or separately purchased mounting bracket, usually in the immediate vicinity of the boiler. The wall must be able to bear the weight of the filled cylinder (empty weight approx. 34 kg + approx. 125 kg of water), so for plasterboard or otherwise non-load-bearing partitions, a suitable mounting system must be used or the cylinder placed on a load-bearing masonry wall.

Cold and hot water connections and the exchanger circuit are connected according to the manufacturer's diagram, usually directly to the boiler or via a manifold. We recommend installing shut-off valves, a safety valve at the cold water inlet, and a check valve. Entrust installation to a qualified plumber/heating technician, who will also connect the control system (temperature sensor, three-way valve) in cooperation with the boiler's control unit.

Maintenance and service

To ensure the ATTACK Wall-Mounted Cylinder OKC 125/1m2 lasts as long as possible, 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
• Descaling/draining the tank via the drain valve once every 1-2 years, especially in areas with harder water, where limescale and sludge settle at the bottom of the tank
• Checking the safety valve on the cold water supply - regularly turning it to verify its functionality and the patency of the drip pipe
• Checking the tightness of connections and the exchanger during each annual boiler service inspection
• In the case of hard water, consider installing a water softening or dosing device, which significantly extends the service life of both the exchanger and the tank

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

Safety, standards and legislation

The ATTACK Wall-Mounted Cylinder OKC 125/1m2 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 regulations for pressure equipment. Correct installation always includes a properly sized safety valve at the cold water inlet, which protects the tank from excessive overpressure during heating - its discharge/drip pipe must be led freely into a sloped space and must not be closed or blocked 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 supply that prevents water from flowing back into the water supply network during heating and thermal expansion). Without an expansion vessel, the safety valve may open repeatedly, causing unnecessary water loss.

Installation, connection to the boiler's heating circuit, and initial commissioning should always be entrusted to a qualified person authorized to install gas and heating equipment. Only professionally performed installation and a regular annual service inspection (together with a boiler inspection) are also a prerequisite for warranty recognition 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 Cylinder OKC 125/1m2 belongs to the Z series - indirectly heated DHW cylinders of the ATTACK brand, which, in addition to this model, also includes other volumes (100, 125, 160, 200 litres), designs (floor-standing OKH NTR/HV, wall-hung OKC, horizontal wall-hung OKCV) and special variants (e.g. with an additional 2.2 kW electric element built into the cylinder body, solar version SOL with two exchangers, or the HP version designed for heat pumps). Thanks to the wide range of variants, it is possible to find a cylinder tailored exactly to the boiler room layout and household needs.

This model is recommended to be combined primarily with floor-standing 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, as the boiler itself does not include a DHW cylinder.

Frequently Asked Questions

Do I need a boiler in addition to the 125 l cylinder, or does it work on its own?

The ATTACK Wall-Mounted Cylinder OKC 125/1m2 is an indirectly heated type - it does not produce heat on its own. It always needs to be connected to a heat source, most often a floor-standing ATTACK gas boiler with provision for an external DHW cylinder (via a three-way valve), or 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, however we recommend rather the specialized HP series models (for heat pumps, with a large-area exchanger for a low-temperature source) or SOL (with an additional solar exchanger), which are directly sized for these sources. This model from the Z series 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 compared to the water temperature. In general, under normal conditions, the cylinder retains a usable water temperature for roughly several hours up to overnight; for a longer standby period without the boiler, it is advisable to add the optional electric heating element.

Is it possible to purchase electric backup heating?

Yes, the cylinder has a provision (pocket/outlet) for an electric heating element with a thermostat, which is purchased separately (for example, 2-6 kW output 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 that installation conditions and regular maintenance (especially 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's 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 is mainly in capacity - a larger volume means more accumulated hot water available at once (e.g. when filling a bathtub while showering simultaneously), but also larger physical dimensions and weight. The choice depends on the number of people in the household and water usage habits.

Can an ordinary wall bear the weight of the filled cylinder?

A filled cylinder weighs a total (empty weight + 125 l of water) of roughly 159 kg, so it must be anchored to a load-bearing masonry wall with suitable anchors, or a separate stand should be used. On thin non-load-bearing partitions (e.g. plasterboard), the wall-hung cylinder must not be installed without additional reinforcement.

Warranty and service

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