A dripping ball valve on your water tank is one of the more common household plumbing issues in New Zealand, and in many cases it's something a confident DIYer can tackle. However, it's important to understand what's causing the drip before you reach for the tools — and to know when the job crosses into restricted plumbing work that legally requires a licensed professional.
What Is a Ball Valve and Why Does It Drip?
A ball valve (also called a float valve or ballcock) is the device inside or on top of your water tank that controls the water level. It uses a floating ball or cup attached to an arm; as the water level rises, the float rises with it and shuts off the incoming water supply. When the valve drips or runs continuously, it usually means one of the following:
- The rubber washer or seat inside the valve is worn or damaged
- The float is waterlogged or cracked and sitting too low
- The float arm is bent incorrectly, keeping the valve partially open
- There is debris or grit lodged in the valve seat
- The valve body itself is cracked or corroded and needs replacing
Identifying the cause first will save you time and money.
Is This DIY or Restricted Work?
This is an important question in New Zealand. Under the Plumbers, Gasfitters and Drainlayers Act 2006, certain plumbing work is restricted and must be carried out by (or under the supervision of) a licensed tradesperson.
Generally speaking, replacing or repairing fittings on a cold-water storage tank (such as a header tank or rainwater tank) that is not directly connected to the pressurised mains supply may be considered maintenance a homeowner can perform. However, if the ball valve is on a mains-pressure system or connected directly to the toby (water meter/stopcock), the work may be restricted. When in doubt, check with the PGDB or consult a licensed plumber — it's always better to be safe than to risk a fine or an insurance issue.
Tools and Materials You'll Need
Step-by-Step: Fixing a Dripping Ball Valve
1. Isolate the Water Supply
Before doing anything, turn off the water supply to the tank. This may be a gate valve or ball valve on the inlet pipe. If you can't find an isolation valve, you may need to turn off the mains at the toby — check with your local council if you're unsure where this is located.
2. Drain Down the Tank (if needed)
For a header tank or low-pressure storage tank, tie up the float arm to stop water entering, then allow the tank to drain to a workable level. Have your bucket ready.
3. Remove the Ball Valve
Using your spanner, undo the locking nut that holds the valve in place on the tank wall. Take care not to damage the tank fitting. Once removed, disassemble the valve body to access the washer and seat.
4. Inspect and Replace the Washer
The washer is usually a small rubber disc held in place by a screw. If it's flattened, cracked, or hardened, replace it with a matching size from your washer kit. While you're in there, check the valve seat for scoring or debris — clean it gently with a damp cloth.
5. Check the Float
Shake the float — if you can hear water inside it, it's waterlogged and needs replacing. Unscrew or unclip it from the arm and fit a new one. Also check that the float arm is straight and set to the correct angle so the valve shuts off at the right water level (typically 25–50 mm below the overflow pipe).
6. Reassemble and Test
Wrap any threaded connections with PTFE tape (2–3 turns), reassemble the valve, and refit it to the tank. Slowly restore the water supply and watch the valve carefully. The water should rise, the float should lift, and the valve should shut off cleanly with no dripping.
Adjusting the Float Arm
If the valve is still running after a new washer, the float arm may need adjusting. On older brass arms, you can gently bend the arm downward so the float shuts the valve off at a lower water level. On modern plastic arms, there is usually an adjustment screw or clip — check the manufacturer's instructions.
When to Call a Professional
Call a licensed plumber if:
- The valve is on a mains-pressure system or you're unsure of the setup
- The tank fitting (the threaded boss in the tank wall) is cracked or leaking
- You find corroded or damaged pipework around the tank
- The overflow pipe is discharging continuously and you can't identify why
- You're not confident working with plumbing fittings
A qualified plumber will also ensure the work complies with the NZ Building Code, particularly Clause G12 (Water Supplies), which sets standards for water supply systems in New Zealand homes. You can find a trusted local plumber on tradedirectory.co.nz.
Safety Note
Always isolate the water supply before starting work. If your tank is elevated, use a stable ladder and have someone nearby. Never work on a hot-water cylinder ball valve without also isolating the power or gas supply to the cylinder — hot-water cylinder work is restricted work and must be done by a licensed plumber.