Unit 204: Cold water storage and float valves

In a typical indirect domestic arrangement, a cold-water storage cistern supplies selected outlets and feeds the vented hot-water cylinder. Trace the actual connections: it does not follow that every outlet except the kitchen tap is cistern-fed. Keep this stored domestic water distinct from the primary heating water served by a separate feed-and-expansion cistern.

Protect the stored water

Use a suitable close-fitting cover and screened openings to exclude contamination. Arrange storage and draw-off for regular turnover, with access for inspection and cleaning. Provide adequate support to prevent distortion when full. Insulation and siting should limit unwanted warming and reduce frost risk; insulation alone is not a guarantee against freezing.

Check the inlet control

The float rises with the water and operates the valve to stop filling at the set level. Select the valve and seating for the supply conditions and required flow. BS 1212 Part 1 covers piston-type valves and Part 2 covers diaphragm-type valves with copper-alloy bodies. These are construction types, not pressure ratings: both have high- and low-pressure variants. Maintain the appropriate inlet air gap; a valve’s label alone does not establish backflow protection.

Overflow capacity and warning

Provide an overflow pipe and a suitable warning arrangement. A combined warning/overflow pipe may be acceptable for a cistern of 1,000 litres or less; alternative warning arrangements need agreement with the water undertaker.

The discharge must be safe and conspicuous. Do not create a slipping or icing hazard on an access route. Size the overflow to carry the maximum fault inflow, allowing for the effect of screens: meeting the minimum bore does not prove enough capacity. A running warning pipe calls for investigation of the inlet control, not plugging the discharge.