DIY Projects - Drain hot taps
Before work can be carried out on a plumbing system, the relevant section will need to be drained.
Vented Hot Water Cylinder (explanation)
To drain the hot water taps and associated pipework, close the valve on the cold feed to the hot water cylinder and turn on the hot taps. It may seem unusual to close the cold feed to the hot water cylinder, but the hot water cylinder uses the pressure of the water in the head tank, to force the hot water from the cylinder. Thus if you remove the pressure you stop the hot water coming out. Remember that even when the water stops flowing from the hot taps, the hot water cylinder will still be full of water.
If you can't find a valve on the cold feed line to the hot water cylinder, you can tie up the float valve on the cold water head tank as shown and drain the head tank by opening the hot taps.
If you can't isolate the cold feed to the cylinder and want to save the hot water in the cylinder, drain the head tank by turning on the cold taps. This will only work on an indirect cold water system.
Unvented Hot Water Cylinder (explanation)
To drain the hot water taps and associated pipework, you must isolate the cold water feed to the cylinder, this can be done by closing the main stopcock on the rising main, where it enters your property or by closing a stopcock local to the cylinder if one has been fitted and turning on the hot taps. It may seem unusual to close either stopcock, but the hot water cylinder uses the mains pressure feeding the tank, to force the hot water from the cylinder. Thus if you remove the pressure you stop the hot water coming out. Remember that even when the water stops flowing from the hot taps, the hot water cylinder will still be full of water.
Combination Boiler
To drain the hot water taps and associated pipework, close the valve on the hot water outlet pipe as it leaves the combi or close the stopcock on the cold water feed supplying the combi and turn on the hot water taps.
DIY Projects - Drain hot water cylinder
Before work can be carried out on a plumbing system, the relevant section will need to be drained.
Switch off any immersion heaters or boilers. Close the valve on the cold feed to the cylinder or drain the cold water storage tank and turn on the hot water taps.
There is normally a drain cock located at the bottom of the cylinder, connect a hose pipe and drain the water into a sink or drain that is lower than the cylinder. Open the drain cock by turning the square spindle using either a drain cock key or an adjustable spanner.
If the hot water cylinder is indirect there will be a coil of pipe inside the cylinder that is full of water which needs to be drained. This can be drained from the drain cock for the heating boiler. If the boiler is part of a central heating system then to save draining all the radiators, close all the valves on both sides of the radiators before opening the drain valve.
When closing a lockshield valve used for balancing the system, make a note of the number of turns so that each lockshield can be opened to the original position.
Syphoning the Hot Water Cylinder
If there is no drain cock for the hot water cylinder or if the drain cock is seized, the water can be drained by syphoning. Disconnect the vent pipe from the top of the cylinder, insert a hosepipe and syphon the water into a drain or sink.