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Lifting the Lid on Your Cistern; Understanding Your Toilet’s Fill and Flush Functions


What are fill and flush valves?

Fill and flush valves are devices that control the water flow in a toilet cistern. They enable the cistern to fill with water and control the flow of water from the cistern into the bowl when you flush your toilet. 

The fill valve regulates the water level in the tank. It utilises a float that rises or falls with the water level, opening or closing a valve that allows or blocks water from entering the tank. 

The flush valve controls the water flow from the tank to the bowl. It has a handle or a button that that activates a mechanism allowing water to pass into the toilet bowl. The flush valve can also have an overflow that prevents water from spilling over the tank when it is full.

What are the advantages of properly maintaining your fill and flush valves?

Fill and flush valves are easy to install, maintain, repair, and replace. They are durable, reliable, efficient, quiet, safe, and environmentally friendly.

It is important to maintain your cistern valves as you would with any other type of mechanical household equipment. This can help avoid failure of the valves or ‘leaky loo’ situations which can waste a lot of water and substantially increase your monthly water bill. 

What are some common types of fill and flush valves?

There are many types of fill and flush valves available in different shapes, sizes, materials, and designs with a variety of features. The type of cistern you have in situ will determine what kind of replacement valve you require. 

We offer replacement flush and fill options for virtually every cistern on the UK market, including bottom or side entry fill valves, button or lever action dual flush valves, dual flush syphons and pneumatic flush valves. 

Here are our recommendations for just some of most versatile and efficient filling and flushing options available from Fluidmaster. 

  • Delayed Fill Valves

In some conditions it is possible for your fill valve to begin filling the cistern once whilst the flush valve is still emptying water into the pan. This is due to the fill valve being activated by a drop in water level. As a result, this can cause “over-flushing”, potentially wasting up to 1L of water with every flush. Delayed-Fill valves offer a solution to this wastage by slightly delaying fill valve activation, allowing the flush to finish completely before refill. Don’t worry though, this doesn’t affect the performance or your toilet as your cistern will still flush the correct amount of water.

The Fluidmaster AirGap 6000 series is our revolutionary, next generation toilet cistern fill valve. The delayed fill models feature a water saving capability which allows a saving of up to 1L of water with every use. With side and bottom entry models to fit virtually all cisterns, these valves are easy to install and service, with no specialist tools required.

Our side entry Fluidmaster Airgap 6000 offers: 

  • Brass shank which prevents cross threading
  • Spiral vortex generator for quiet cistern refill
  • Airgap technology – prevents back siphonage and the need for an additional check valve
  • Fully recyclable

The bottom entry Fluidmaster Airgap 6000 offers all of the same features as the side entry version, plus height adjustment which is quick and easy, by simply sliding the valve to the desired height, then fine tuning with the adjustment screw.

  • Dual Flush Cable Valves

Our versatile, button cable dual flush valve can be top, side, or front mounted. It fits both 1 1/2″ and 2″ outlets and incorporates a fully height adjustable overflow with no cutting required. The twist and release action is ideal for easy maintenance and the quick release cable/button eliminates problematic cable damage.

Water saving dual flush functionality ensures that this flush valve will offer maximum efficiency, with adjustable flush volumes for full and partial flush. 

  • Fits both 1 1/2″ and 2″ flush outlets
  • Cable length 3500mm
  • Adjustable overflow from 8 1/2″ to 13 1/2″
  • Dual flush button fits top, front or side applications
  • Mechanical Flush Valves

Our mechanical dual flush valve with water saving adjustable flush volumes fits virtually all top button activated cisterns with a 2″ outlet. It offers water saving adjustable flush volumes for full and partial flushes, plus a twist and release action to enable simple maintenance.

This rod operated mechanical flush valve is suitable for use with close-coupled toilets. And the overflow and rod lengths are adjustable, making this valve suitable for virtually all top button activated cisterns with a 2″ outlet.

  • Easy rod length adjustment
  • Overflow adjustable from 170mm to 250mm
  • High quality chrome button with easy flush volume distinction
  • Durable silicone seal
  • Pneumatic Flush Valves

The popular pneumatic flush valve is a modern, efficient flushing option. Operated using pneumatic tubes which are connected to the outlet valve; when the flush button is activated, air is used to lift the flush and release water into the cistern. 

  • Adjustable dual flush
  • Twist and release for easy removal 
  • Compatible with a variety of pneumatic flush plates 
  • Front or top activation available
  • Syphons

Our ultra compact syphon for lever operated toilets is quick and easy to install and service. It offers rapid height adjustment, flush volume adjustability and light touch activation.  The unique full and partial flush volume adjustability gives you full control over the water delivered to the pan. Owing to the syphon mechanism, it offers leak-free flushing ensuring that no water is wasted when the toilet is not in use. 

  • Ultra compact syphon
  • Easy to install
  • Rapid height adjustment – 7.5 – 9.5 inch
  • Full and partial flush adjustability
  • Retrofits other syphons

In Conclusion

Fill and flush valves are vital components of any modern toilet that ensure proper functioning, sustainable water use, and protection of the toilet system. Choosing the right one for your toilet depends on your preferences, and your current cistern arrangement. 

If in doubt, always consult a qualified plumber before adjusting, removing, or replacing any parts in your toilet cistern.