Geyser pressure-release valve dripping: normal or a fault?

The small valve on the cold inlet is the geyser's safety release. Understanding what it is for makes it obvious when its behaviour is wrong.

What it does

Water expands when heated. In a sealed tank that expansion has to go somewhere, or pressure climbs. The valve opens briefly and lets a little out. It also opens if inlet pressure is too high, protecting the tank.

Normal

A few drops or a short dribble from the spout during a heating cycle, then dry. If you see a small puddle that does not grow, that is the valve working.

Not normal

• A steady drip all the time, geyser on or off
• A trickle that never stops
• No water at all, ever, even when heating — the valve may be seized shut
• Water from around the valve body rather than the spout

Causes of a constant drip

The valve seat is worn or has scale on it, and it no longer closes fully. Or the mains pressure is high enough to hold it open — common on ground floors with an overhead tank far above. The first is a new valve. The second is a pressure-reducing valve on the inlet.

Never cap, plug or wire the release valve shut to stop a drip. It is the only thing between an expanding tank and a burst one.

The fix

A worn valve is a standard part and a quick swap with the supply isolated. If the drip continues with a new valve, pressure is the cause and a reducer goes on the inlet.