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Draining the system

• In order to repair a leak, run new pipes or service a toilet cistern, it is necessary to be able to drain various parts of the system.
  
• Water is supplied to a house under relatively high mains pressure. In most houses it is directed via the rising main pipe to a cold water storage cistern in the loft. A pipe connected to the rising main feeds drinking water directly to the kitchen sink. All other taps and fittings, including the hot water storage cylinder, are supplied indirectly by a low pressure gravity fed system from the storage cistern.
  
• To drain the cold water kitchen tap and pipe, close the stopcock on the rising main, then open the tap to empty the short length of pipe.
  
• Drain cold water taps in the bathroom by shutting off the cold feed valve from the storage cistern in the loft. Now run the bathroom taps.
  
• If there is no isolating valve, shut off the supply of water to the cistern by tying the arm of the float valve to a batten placed across the top. Then run the taps to drain the entire cistern. Use this method if you ever need to work on the cistern itself.
  
• To drain a toilet cistern, tie up its float-valve arm and flush the toilet. If you need to work on the supply pipe to the cistern, shut off the water supply from the storage cistern in the loft.
  
• To drain hot water taps, first turn off the immersion heater and central heating boiler, then shut off the supply of water from the storage cistern in the loft to the hot water cylinder. Run off the water from the hot taps.
  
• If you want to drain the hot water cylinder itself, attach a hose to the draincock at the base of the cylinder. If the cylinder contains a heat exchanger fed from the boiler, this can only be emptied through the boiler draincock.