Four-way mixing valve Termojet, DN25, kvs-12 female thread

Termojet DN25 four-way rotary mixing valve — the key element for protecting a solid-fuel, pellet, or gas boiler against condensation corrosion. Internal thread Rp 1", flow coefficient Kvs 12 m³/h, working pressure PN 10 bar, temperature range –10…+110°C. Body — CW617N brass, EPDM seals. The valve simultaneously solves two tasks: it blends hot water from the boiler into the return pipeline and regulates the supply temperature to the heating circuit.

Technical Specifications

Operating Principle

The valve has four ports: K+ — supply from the boiler, K– — return to the boiler, H+ — supply to the circuit, H– — return from the circuit. When the disc rotates 90°, both flows are regulated simultaneously. When cold return fluid comes from the circuit, the valve blends part of the hot supply into the K– pipeline, raising the return temperature before it enters the combustion chamber. Simultaneously — it lowers the H+ supply temperature by mixing hot with return fluid.

Why this is critical for a solid-fuel boiler: when the return temperature falls below the dew point (60–65°C for wood), moisture condenses in the combustion chamber — causing corrosion, tarring, and a sharp reduction in service life. The four-way valve guarantees that the boiler always receives return fluid above the dangerous threshold.

Applications

• Solid-fuel boiler (wood, pellets) up to 30 kW. DN25, Kvs 12 — the optimal size for boiler rooms of 15–30 kW: protection against condensation and tarring during system warm-up or partial load.
• Non-condensing gas boiler. Maintaining return temperature above 55°C to protect the heat exchanger from scaling and corrosion.
• Boiler + buffer tank. The 4-way valve controls the flow between the boiler, thermal storage, and circuit — the boiler does not receive cold water from the buffer tank.
• Stove with a water circuit. Protection against thermal shock during lighting — while the system is cold, the valve recirculates hot heat transfer fluid within the boiler.
• Bivalent system (heat pump + boiler). The valve controls blending when the backup boiler is connected — the boiler does not receive cold return fluid from the heat pump circuit.

Advantages of Termojet DN25

• Kvs 12 in DN25 size — higher flow capacity for boiler rooms up to 30 kW: lower hydraulic resistance in standard DN.
• CW617N brass body — corrosion resistance and manufacturing precision on par with leading equivalents.
• Disc torque below 3 Nm — compatible with 6 Nm actuators with double the torque margin.
• EPDM seals — resistance to glycol-based heat transfer fluids and elevated temperatures.
• A worthy replacement for imported DN25 four-way valves — no customs delays, standard Rp 1" thread.

Compatible Actuators

Disc torque of the DN25 valve — below 3 Nm. All listed actuators have double the torque margin:

• Termojet 401N electric actuator (3-point, 230V) — fast control for simple boiler room schemes.
• Termojet 405N electric actuator (3-point, 230V) — smoother control, the standard choice for most boiler rooms.
• Termojet 411 electric actuator (0–10V, 24V) — for weather-compensated control and smart home integration.
• Termojet 413 actuator-controller — autonomous actuator with built-in sensor and controller: maintains the set return temperature without a separate controller.

Valve and Heat Pump

In bivalent systems where the heat pump is the primary heat source and the solid-fuel or gas boiler is the backup, the Termojet DN25 four-way valve manages boiler connection without the risk of condensation corrosion. When the boiler is switched on into a cold system, the valve recirculates heat transfer fluid within the boiler circuit until a safe return temperature is reached. About bivalent solutions with a heat pump — on the Termojet heat pumps website.

Frequently Asked Questions

Why a 4-way valve when a 3-way valve exists?
A 3-way valve either mixes the supply temperature or protects the return — but not simultaneously. The 4-way valve solves both tasks in one body: it blends hot water into the return pipeline (boiler protection) while simultaneously regulating the supply temperature to the circuit. For solid-fuel boilers — a fundamental difference.

How does DN25 Kvs 12 differ from DN32 Kvs 18?
DN25 — for boiler rooms up to 30 kW. DN32 Kvs 18 — for larger systems of 30–60 kW. Choose DN according to your boiler's output and calculated heat transfer fluid flow rate.