Antifreeze valve Termojet DN25 (1" M)

The Termojet DN25 antifreeze valve (thread 1"M) is a brass automatic safety device that protects the heating system against the destructive consequences of freezing. When the coolant temperature drops to the critical threshold of ≈+3°C, the valve opens automatically and drains a portion of the coolant, preventing ice expansion and the bursting of pipes or radiators. Once normal temperature is restored, the valve returns to its default closed state without any operator intervention.

Technical Specifications

Operating Principle

Inside the valve is a thermosensitive element — a wax capsule or liquid bellows — that responds to the ambient temperature around the body. When the coolant temperature in the pipeline drops to ≈+3°C, the thermoelement expands, pushes the valve plug and opens the drain. A portion of the coolant is discharged into the sewer or drainage system — pressure in the pipe drops, and the risk of ice-induced bursting is eliminated.

Once the system heats up again (upon reconnection of the boiler, heat pump, or restoration of heat supply), the thermoelement returns to its initial position and the valve closes. No automation, sensors, or cables are required — the valve is fully autonomous.

Applications

• External circuits and pipelines in unheated spaces. Basements, garages, entrance halls, technical shafts — where temperatures can drop below zero when heating is switched off.
• Heat pump systems. External circuits of ground-source and air-source heat pumps remain unheated in the event of an emergency shutdown — the antifreeze valve protects the pipework from damage even during prolonged downtime.
• Seasonal properties — country houses, cottages, farmsteads. If a building is unheated in winter or there is a risk of prolonged power outage, the valve protects the entire system autonomously, without the owner being present.
• Pipelines in frost-prone zones. Distribution runs under the ground floor or in the walls of the outer perimeter — where the risk of freezing is highest if the boiler fails in winter.
• DN25 — for small and medium-diameter systems. Compatible with G1"/DN25 pipes, standard for single-pipe and two-pipe heating systems in private homes. For larger mains — Antifreeze valve DN32.

Advantages of Termojet DN25

• Fully autonomous — no power supply, no automation, no maintenance.
• Instant response at ≈+3°C — activates before the water freezes and bursts the pipe.
• Brass body — corrosion-resistant and compatible with all common heat transfer fluids.
• Maximum pressure 10 bar — suitable for closed heating systems at any pressure within normal limits.
• Self-restoring after warm-up — no replacement or resetting required after each activation.

Antifreeze Valve and Heat Pump

Heat pumps are often installed in homes with seasonal or irregular occupancy. In the event of an emergency heat pump shutdown in winter — due to power outage, control fault, or compressor failure — the external pipework quickly cools to ambient temperature. The DN25 antifreeze valve protects the pipework from bursting in such situations, acting fully autonomously. Learn more about reliable heat pump systems on the Termojet heat pumps website.

Frequently Asked Questions

Where does the coolant drain when the valve activates?
The valve must be connected to an open drainage channel or sewer via a hose or rigid pipe of the appropriate diameter. When installing, ensure a drain outlet is provided in an accessible location — just as for a boiler safety valve.

Is all the coolant lost when the valve activates?
No. The valve opens for a minor pressure release — just enough to prevent critical pressure from ice expansion. It closes after warm-up. However, after each activation it is recommended to check the coolant level and top it up to normal pressure. More useful accessories are available in the Termojet additional equipment catalogue.