Product detailed description

ATTACK Z 200 OKC - indirectly heated domestic hot water cylinder

The ATTACK Z 200 OKC cylinder belongs to the popular range of wall-hung indirectly heated OKC cylinders, which are designed from the factory to be hung directly under common wall-hung gas boilers, or mounted separately on the wall using a bracket in close proximity to the boiler. A volume of 200 litres represents a balanced compromise between space requirements and hot water comfort for a household of 2 to 4 members, with a bathroom featuring both a shower cubicle and a bathtub.

How an indirectly heated cylinder works

Unlike cylinders with their own heat source (electric or gas), the Z 200 OKC cylinder is so-called indirectly heated - the water inside it is heated by a heat-transfer medium (heating water) flowing from the boiler through a built-in coil-shaped steel heat exchanger located inside the tank. During DHW heating, the boiler thus switches operation between the heating circuit and hot water preparation, usually giving priority to DHW, so the water heats up quickly even with a common boiler output of 20-24 kW. The cylinder itself therefore never operates independently - it requires connection to a functioning heat source (gas, electric or solid fuel boiler, or a heat pump).

The water intended for consumption (drinking, domestic use) is separated from the heating water in the exchanger - it only flows through the interior of the tank around the coil, never mixing with water from the heating circuit. This design is maintenance-free in terms of the chemical composition of the water and ensures that even if the quality of the heating water deteriorates, the domestic water remains clean and hygienically safe.

Key features

• Volume of 200 litres, vertical cylindrical design for hanging under the boiler or on the wall
• Enamelled steel tank with a magnesium sacrificial anode against corrosion
• One heating coil for connection to a gas, electric or solid fuel boiler
• Hard, freon-free PU insulation with low heat losses
• Compact dimensions suitable even for small utility rooms and bathroom cores
• Simple installation directly under the wall-hung boiler using a connecting kit (not included)
• Built-in immersion sleeve for the boiler's thermometer/thermostat
• High-quality plastic top and bottom cover, resistant to UV radiation and mechanical damage
• Ready to be fitted with an electric heating element (e.g. ATTACK TH) via a 6/4" threaded flange

Technical parameters

Assembly and installation

The Z 200 OKC cylinder is installed either directly by hanging it under the body of a wall-hung boiler using a connecting (bracket) kit, which creates a compact boiler + cylinder unit on a single wall, or separately on its own bracket next to the boiler. In the second variant, connection using copper or steel piping is required on the heating circuit side (heat exchanger) and on the hot and cold water distribution side. We recommend not forgetting the DHW safety valve with an opening pressure of max. 0.6 MPa and a check valve on the cold water inlet, as well as an expansion vessel on the DHW side for longer piping runs or closed systems.

Connection to the heating circuit (boiler) is carried out via a pair of heat exchanger outlets (inlet/outlet) with a circulation pump and a three-way diverter valve - in most modern ATTACK boilers, this logic is controlled directly by the boiler's electronics, which prioritise interrupting the heating circuit when DHW is requested. For boilers of other brands, an external three-way valve and a room or cylinder thermostat need to be added.

Installation should be carried out exclusively by a qualified technician authorised to install pressure vessels and DHW piping, who will also check the functionality of the safety equipment and issue the necessary commissioning documentation.

Maintenance and service life

For a long service life of the cylinder, we recommend checking the condition of the magnesium anode once a year (more often in harder water) and replacing it if worn (diameter reduced by more than half). At the same time, it is advisable to visually check the safety valve by briefly opening it and check the tightness of the exchanger's flange closure. Regular servicing significantly extends the tank's service life beyond the warranty period and reduces the risk of limescale build-up on the exchanger.

Step-by-step commissioning procedure

1. Verify the correct position and fixing of the cylinder (hanging under the boiler or on a bracket next to it, checking the wall's load-bearing capacity)
2. Connect the exchanger to the boiler's heating circuit, including the circulation pump and any three-way diverter valve
3. Connect the cold water supply with a check valve and DHW safety valve (max. 0.6 MPa)
4. Connect the hot water supply to the points of use, or install a circulation pipe for longer distribution runs
5. Fill the cylinder with water and thoroughly vent it via the highest-positioned outlet valve
6. Fill and vent the heating circuit on the exchanger side
7. Set the desired DHW temperature on the boiler or cylinder thermostat (recommended 55-60 °C)
8. Perform a functional test of the safety valve and check the tightness of all joints under pressure
9. Hand over documentation (manual, warranty card) and instruct the user on operation and basic maintenance

Safety warnings

The cylinder is a pressure vessel and must always be fitted with a functional safety valve with an opening pressure corresponding to the maximum operating pressure (0.6 MPa) - the safety valve must never be closed off or otherwise disabled. The discharge from the safety valve (drip pipe) must be led freely into the space with a downward slope, and must never be sealed with a plug. When operating with a solid fuel boiler without accumulation, we also recommend adding a thermal safety valve on the heating circuit side to protect against overheating. Work on the gas, electrical and pressure-related parts of the system should be entrusted exclusively to appropriately authorised persons.

Operating economics

The operating costs of the indirectly heated Z 200 OKC cylinder are determined practically exclusively by the price of the fuel/energy used in the connected heat source (boiler) - the cylinder itself does not consume any energy, its role is only to store and release heat. The cylinder's high-quality PU insulation minimises spontaneous heat losses when water is not being drawn (so-called standby losses), and together with a correctly set DHW temperature (recommended 55-60 °C, not higher than necessary for comfort and hygiene), it contributes to lower overall fuel consumption for hot water preparation throughout the year.

Who is the Z 200 OKC suitable for

This cylinder is an ideal choice for households that already have, or are planning to install, a new wall-hung gas boiler and are looking for a compact hot water preparation solution without the need to build a separate boiler room. 200 litres is sufficient for everyday use by a 2-4 member family (showering, kitchen, washing); for higher expected consumption (multiple bathrooms, bathtub and simultaneous showering), we recommend considering a volume of 300 l or more from the ATTACK Z / AS / TUV range.

How to navigate the ATTACK Z / PZO cylinder range

The ATTACK brand offers several types of hot water cylinders that differ in their heating method and purpose. Below is a brief overview to help you orient yourself when choosing a related or replacement product:

• Z .. OKC / OKCV ▸ this is exactly the product you are viewing - A basic indirectly heated cylinder with one exchanger, connected to a boiler. The simplest and most affordable DHW preparation solution if you already have or are planning a boiler.
• Z .. OKC ENTR HV 2.2 - Same principle as OKC, plus a built-in 2.2 kW electric heating element - a choice for cottages, summer operation without a boiler, or as a backup in case of boiler failure.
• Z .. SOL - Two exchangers - a boiler exchanger and a large-area solar exchanger. A choice for households with solar collectors that want to make use of free solar heat as well.
• Z .. HP - One large-area exchanger optimised for the low output temperatures of a heat pump. A choice for households with a heat pump as the main heat source.
• PZO .. PLUS - Directly heated, with its own gas burner, requires no boiler at all. A choice for cottages, workshops and premises without central heating.

With all indirectly heated variants (OKC, ENTR, SOL, HP), the heating output can be supplemented or backed up with an ATTACK TH electric heating element (outputs 2/2.5/4.5/6 kW) via a 6/4" flange, which is available in our range as a separate product.

Common mistakes when choosing and installing

The most common mistakes when choosing and installing indirectly heated cylinders include underestimating the volume relative to the household's actual consumption (especially when adding a bathroom or increasing the number of household members), forgetting the DHW safety valve or sizing it incorrectly, incorrectly set DHW heating priority on the boiler (the cylinder heats up slowly because the boiler prioritises the heating circuit), and neglected inspection of the magnesium anode, which, if completely worn out, can lead to premature corrosion of the tank. For the Z 200 OKC model, we also recommend checking the available space and the wall's load-bearing capacity in advance if you plan to hang it directly under the boiler.

Frequently asked questions

Can I connect the cylinder to any gas boiler?

Yes, the cylinder can be universally connected to most wall-hung and floor-standing boilers (gas, electric and solid fuel) via the heat exchanger. For boilers without their own DHW/heating switching logic, an external three-way valve and a cylinder thermostat need to be added.

Do I need to order anything else together with the cylinder?

Yes - a connecting/bracket kit for hanging (depending on the boiler type), a DHW safety valve, and possibly a three-way valve and thermostat if the boiler does not have its own DHW preparation control.

Can an electric heating element be added to the cylinder?

Yes, the cylinder has a 6/4" flange opening ready for fitting an ATTACK TH electric heating element with an output of 2-6 kW, which serves as a backup or supplementary heat source when the boiler is out of operation.

What is the actual heating time for the whole volume?

With a typical boiler with an output of approx. 24 kW and DHW priority set, the cylinder usually heats up from 15 °C to 55-60 °C within 20-30 minutes; the exact time depends on the boiler's output, the heating water temperature and the condition of the exchanger.

How often does the magnesium anode need to be replaced?

The recommended inspection interval is once a year, with replacement depending on wear, typically every 1-3 years depending on the water hardness in the given location.

Can the cylinder be used horizontally as well?

No, this Z 200 OKC model is intended exclusively for vertical installation. For horizontal (loft/attic) installation, the OKCV variant (right/left) is available.

How much space does the cylinder take up?

Approximate dimensions are a diameter of 550 mm and a height of 1150 mm, which, when hung under the boiler, practically does not increase the floor area of the utility room.

Is a safety valve or connecting kit included in the package?

No, the safety equipment, connecting and mounting kits are ordered separately depending on the type and brand of boiler; we will be happy to advise you when choosing.

Can the cylinder also be used with a solid fuel boiler (wood, pellets)?

Yes, the exchanger is also suitable for solid fuel boilers; however, for boilers without an accumulation tank, we also recommend adding a thermal safety valve on the heating circuit side to protect against overheating.

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

Thanks to the high-quality PU insulation, heat losses are low; the cylinder typically loses only a few degrees of temperature over 24 hours without draw-off and without reheating - the exact value depends on the temperature difference relative to the surroundings.

Can the cylinder be relocated to another room later on?

Yes, the cylinder is not permanently tied to a specific location; however, when relocating it, the DHW and heating circuit connections must be reconnected and the functionality of the safety equipment must be checked at the new location.

Is there a difference between OKC and the older NTR/HV models from ATTACK's range?

These are related ranges of cylinders with a similar indirect heating principle, differing mainly in shape and installation method (hanging vs. floor-standing design) - when choosing, we recommend basing your decision on the available space and installation method in your boiler room.

Can the cylinder's volume be increased afterwards?

No, the volume is determined by the tank's construction and cannot be changed afterwards - if hot water consumption increases, the cylinder must be replaced with a larger model.

Summary

The ATTACK Z 200 OKC is a proven, affordable solution for hot water preparation for households with a wall-hung boiler - compact, reliable, with a long warranty on the tank and easy installation directly under the boiler. If you are looking for independence from the boiler, solar backup heating, or cooperation with a heat pump, also check out the ENTR, SOL and HP variants from the same Z range in our offer.

Warranty and service

The manufacturer ATTACK provides a 5-year warranty on the cylinder tank from the date of sale, subject to the conditions stated in the warranty card (regular anode inspection, compliance with the maximum operating pressure and temperature, installation of safety equipment in accordance with applicable legislation). The other components of the cylinder (insulation, casing, electrical components, sensors, accessories) are covered by the standard warranty period of 24 months. Service and spare parts for the entire ATTACK range are provided by a network of authorised service partners in Slovakia and the Czech Republic; our team will be happy to advise you on selecting the right part or contacting the nearest service centre if needed.