Replacing a seized stopcock or faulty ballvalve
Stopcock and Ballvalve Replacement
Stopcock and ballvalve replacement covers fitting a new main stopcock where the existing one is seized, leaking or no longer shuts off the supply, and replacing a faulty ballvalve — the float-operated valve that controls water level in a toilet cistern or cold water tank.
Definition
What Stopcock Replacement covers
The stopcock is the main valve controlling the incoming water supply to a property, and needs to work reliably as it's the first thing to shut off in an emergency. A ballvalve is a float-operated valve found in toilet cisterns and cold water storage tanks that controls the water level and shuts off the fill when full; a worn or misadjusted ballvalve causes overflowing or a constantly running system.
Suitable for
- A stopcock that won't turn, won't fully shut off, or is leaking at the spindle
- A ballvalve causing a cistern or tank to overflow or run continuously
- Upgrading an old rising main stopcock as part of other plumbing work
- Fitting an accessible isolation valve where none currently exists
Not suitable for
- The external stopcock in the street, which belongs to the water authority and is not something we replace
- Faults beyond the valve itself, such as a wider supply pressure issue, which need separate diagnosis
Process
How the work is carried out
- 01
Assessment
Checking the condition and accessibility of the existing stopcock or ballvalve.
- 02
Isolating the supply
Shutting off the water at the nearest point upstream, which for a main stopcock replacement may mean the external supply.
- 03
Replacement
Fitting the new stopcock or ballvalve and associated fittings.
- 04
Testing
Restoring the supply and checking the new valve operates and shuts off correctly.
Typical timescale
Stopcock and ballvalve replacement is typically completed within a single visit, usually an hour or two, though access — such as a stopcock under floorboards or a ballvalve in a loft tank — can affect timing.
Cost guidance
Stopcock and ballvalve replacement typically costs £90–£200 per job in our area, with the main factor being access — a stopcock under a kitchen sink is more straightforward than one under floorboards, and a ballvalve in a loft tank takes longer than one in a toilet cistern. We provide an itemised quotation after inspection rather than a fixed headline price.
Limitations and exclusions
- Where the external supply cannot be isolated without the water authority's involvement, this is arranged in advance and may affect timing
- Any wider pipework found to be in poor condition during the visit is flagged and quoted separately
Areas we cover
Stopcock Replacement across Sussex, Surrey, Kent and South London
Local property styles, planning authorities and neighbourhood coverage for stopcock replacement in each town we work in.
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FAQs
Stopcock Replacement FAQs
Why won't my stopcock turn?
This is usually corrosion or scale build-up inside the valve after years of not being used — stopcocks that are never turned tend to seize. We recommend testing yours periodically, and if it won't move, replacing it before you actually need it in an emergency.
How do I know if my ballvalve needs replacing?
Common signs are a cistern or tank that keeps overflowing, runs continuously without settling, or a float that has become waterlogged and sits low. Sometimes an adjustment or new washer is enough, but on an older valve, replacement is usually more reliable.
Can you fit an isolation valve so I don't have to use the main stopcock every time?
Yes, local isolation valves under sinks, at toilets, or serving individual appliances make it much easier to isolate a single fixture without shutting off the whole property, and are often fitted as part of other plumbing work.
Discuss your stopcock replacement project
Tell us about the property and what you have in mind, and we'll arrange a site visit.
Last reviewed 2026-07-28.