Warning pipe
In plumbing · also called Overflow
A pipe from a cistern that discharges somewhere easily noticed, such as outside or into the toilet pan, when the water rises above its normal level. Water running from it is a sign that the float valve is not shutting off, and it is there to be noticed and dealt with rather than ignored.
Using Warning pipe in a plumbing system
Updated
A distinction worth remembering
Backflow can result from a pressure drop upstream or higher pressure downstream. An arrangement suitable for one fluid category may be unsuitable for another. Water Regs UK explains the differences between backflow devices and air-gap arrangements; the water supplier can advise on the applicable case.
Questions to take further
- Is a double check valve suitable for every backflow risk?
- No. Protection must match the fluid category and the pressure conditions. Higher-risk uses can need an appropriate air gap or other suitable arrangement; do not choose a device merely because it fits the pipe.
Sources
- Water Regs UK: backflow protection — Contamination risks and why protection must match the fluid category and conditions.
Where Warning pipe fits in the learning path
The Cold Water Basics section covers these topics:
- The Incoming Water Supply
- Cold Water Storage and Backflow
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- Cold Water Storage and BackflowCold Water Basics
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A valve that fills a cistern and shuts off as the water rises, closed by a float on an arm or a float that slides up a column. Lowering the float lowers the water level it stops at. A valve that will not shut fully lets the water keep running until it reaches the warning pipe.
Float valve
Read the Float valve entryCompare related terms
Open a meaning to compare its role with Warning pipe, or follow its full entry.
Float valve — Ballvalve
A valve that fills a cistern and shuts off as the water rises, closed by a float on an arm or a float that slides up a column. Lowering the float lowers the water level it stops at. A valve that will not shut fully lets the water keep running until it reaches the warning pipe.
Read the Float valve entryCistern — Cold water storage cistern
An open-topped container that holds water at normal air pressure, such as the cold water storage cistern in a loft or the cistern behind a toilet. It is filled through a float-operated valve, and its lid, warning pipe and insulation help keep the stored water clean, stop it overflowing and protect it from frost.
Read the Cistern entryBefore you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.
A definition is a start. Using it in a real question is where it sticks.