Fix a Leaking Cold Water Tank — Loft
A leaking cold water tank in the loft is usually a worn seal or compression olive — a £3 fix caught early. Left unchecked it damages flooring, joists and ceilings below. Here is the trade method.
Step-by-step method
1. Isolate the water
Nearest isolator or property stopcock. Prove zero pressure by opening the cold water tank.
2. Dry and identify
Dry the cold water tank completely. Run 30 seconds. The first bead of water shows the exact fault.
3. Strip and inspect
Remove cover/collar. Inspect washer, O-ring, olive. Take to Screwfix/merchant to match.
4. Refit with new seal
Grease O-rings with silicone (not vaseline). PTFE-tape 5 wraps clockwise. Hand-tight + 1/4 turn.
5. Pressure-test
Open isolators, purge, run 60 seconds. Re-check after 24 hours.
Frequently asked questions
DIY or plumber?+
Non-gas leaks are DIY-friendly. Plumber callout £70–£140.
Emergency?+
Weeping = 24h. Active spraying = same day.
Insurance?+
Sudden damage yes; gradual leaks no.