Stopcocks and Isolation Valves
The stopcock is the main shut-off for your entire water supply, and isolation valves let individual appliances or outlets be shut off without affecting the rest of the house.
The stopcock is the main shut-off for your entire water supply, and isolation valves let individual appliances or outlets be shut off without affecting the rest of the house. Knowing where yours is and that it actually turns is worth checking before you need it in an emergency.
What it does
A stopcock is a full-bore valve, usually under the kitchen sink or near the property boundary, that cuts the mains supply to the whole house; isolation valves do the same job locally at a toilet, tap or appliance.
How it fails
Old stopcocks seize solid from lack of use, or their washers perish and they weep even when fully closed. Isolation valves fitted decades ago often seize the same way.
Repair or replace
A stiff but functional stopcock can sometimes be eased and exercised; one that's seized solid or won't seal is replaced, ideally with a modern quarter-turn valve.
Questions we get asked
Where is my stopcock likely to be?
Most commonly under the kitchen sink, though it can be elsewhere depending on the property — we'll help you locate it if you're not sure.
Is stopcock replacement something a homeowner can arrange freely?
No, this is plumbing work, not gas work.
Should I test my stopcock myself?
Turning it off and on once a year is a sensible check most people can do; if it won't move at all, that's worth having addressed rather than forcing it.