Hot Water Cylinder Leaking? What It Means
Where the water appears tells you how serious it is, from a loose fitting to a cylinder at end of life.
From a fitting or valve
Drips at the immersion boss, a union or the temperature relief valve are usually seals and washers, quick repairs. A relief valve that keeps passing is a warning about pressure or a failed expansion vessel, so the cause matters more than the drip.
From the cylinder body
Weeping from the shell itself, or rust streaks down the insulation, means corrosion has made it through. There is no honest repair for a pinholed cylinder; plan the replacement before it chooses its own date.
The discharge pipe outside
On unvented systems, a dribbling external pipe is the safety system relieving pressure. It is doing its job, but doing it constantly means the expansion vessel or a valve needs attention at the next service.