A pressure relief valve (T&P valve) that keeps dripping or releasing means either the valve is faulty and needs replacing, or your hot water system is operating at too high a pressure or temperature. Both require a plumber — never block or cap a releasing T&P valve.
The T&P relief valve is a critical safety device that opens automatically if pressure or temperature inside the tank reaches dangerous levels — preventing the cylinder from failing dangerously. It's mandatory by NZ law and connects to a drain pipe that discharges away from the cylinder.
The valve releasing is doing its job. But a constantly dripping valve wastes water and indicates a problem that needs attention. Have it inspected within 1–2 days — not weeks.