Check the float valve setting, the warning pipe's conspicuous and safe discharge, its capacity, fall and screens, and the inlet gap it protects.
A storage cistern has to cope with its float-operated valve failing to shut off. The float valve controls normal filling. A warning arrangement makes an excessive level noticeable; the overflow provision must safely carry the maximum fault inflow. One pipe may serve both purposes in a suitable accepted arrangement, while others use separate provisions. Work through these checks:
- Water level: the float valve shuts off with the normal water level below the warning pipe, so the pipe stays dry in normal use.
- Capacity: size and position the overflow provision to carry the full inflow if the float valve fails to close, allowing for screen restriction. A separate warning pipe need not carry that full flow.
- Conspicuous warning: the warning pipe ends where its discharge will be seen, such as through an external wall. Water running there warns of an excessive level, for example from a passing or incorrectly set float valve, so the cause can be investigated and continuing waste or damage limited. A hidden discharge defeats the pipe's purpose.
- Safe discharge: it must not wet a doorway or create an icing hazard on a path.
- Drain connection: if it discharges to a drain, keep the discharge visible through an air break and provide the required backflow protection.
- Fall: the pipe falls continuously to its outlet, so it drains and does not hold water.
- Screens: screen the warning, overflow and vent openings as required by the arrangement to exclude insects and other foreign matter. Keep insect screens accessible and removable for cleaning. A damaged screen is a direct contamination route, so keep screens intact and clear.
- Inlet gap: a rising water level must not reach the inlet. On a type AG inlet, the overflow has to carry the fault inflow without the water rising into the specified gap above the critical water level.
A warning pipe is not a vent or a cylinder feed. If it runs, investigate the excessive level and restore proper control rather than accepting the discharge.