The LavaTap 28mm anti freeze valve protects the outdoor water pipework of a monobloc air source heat pump from freezing without filling the system with glycol. It works on water temperature alone: when the water inside the pipe falls to 3°C (±1°C) the valve opens and lets a small flow drain away, which keeps water moving through the pipe and stops ice forming. When the water warms to 4°C it closes again. There are no electrics, so it keeps working in a power cut, when the heat pump's own frost protection cannot run.

Specifications: CW617N brass body, stainless steel springs, EPDM seals. Connections 28mm compression for copper pipe, two nuts and olives supplied. Maximum pressure 10 bar. System water 0 to 65°C. Ambient -30 to 60°C. Medium: water only. Tightening torque 80 Nm. Replaceable sensor cartridge with automatic shut-off, and a vacuum breaker.

Which one do I need? Choose by the connection where the valve goes. This 28mm version fits into a 28mm copper flow or return pipe. If you want to fit the valve straight onto a heat pump's threaded connection, choose the threaded option that matches it.

How to fit: fit one valve on the flow and one on the return, outdoors near the heat pump. Mount it upright with the drain outlet pointing down and nothing blocking it, at least 15cm above the ground and at least 10cm from the next valve. Do not insulate the valve body, avoid dips or traps in the pipe, and protect it from rain, snow and direct sun. Keep the system pressurised, including while the valve is draining.

Not suitable for systems filled with glycol, for split heat pumps (only refrigerant runs outside), or for heat pumps that run the water above 65°C.

In the box: 1 x anti freeze valve, 2 x 28mm compression nuts, 2 x 28mm olives.

KeyPlumb part code K21711.