Geyser Multi Function Safety Valve (MFSV) 0.8 MPa pressure range, Geyser NRV Safety Valve

The pressure relief valve stops the tank over-pressurising. It is a plumbing job rather than an electrical one, but it is a safety part — if it is weeping or has stopped lifting, replace it rather than removing it.

1. Switch off at the geyser switch and the MCB, and let the tank cool.
2. Close the inlet valve and release the pressure by opening a hot tap, then drain enough that the water level is below the valve.
3. Note which port it screws into and where the discharge pipe runs before removing it.
4. Unscrew the old valve. Support the pipework with a second spanner so you are not twisting the tank connection.
5. Clean the threads and wrap fresh PTFE tape — around four to six turns, in the direction the valve screws on, so tightening does not unwind it.
6. Fit the new valve hand-tight, then a turn or two with a spanner, aiming the discharge outlet downward and where a discharge would be visible and safe.
7. Reconnect the discharge pipe. It must run downward, stay open to atmosphere, and never be capped, valved or plumbed uphill.
8. Refill and check for weeps, then restore power and check again once hot.

A relief valve that drips occasionally when heating is doing its job. One that drips constantly usually means high mains pressure or a failed expansion vessel — worth checking before you fit another valve.