Draining and Refilling a System

All wet central heating systems will be provided with at least one drain cock that to allow the system to be empty for maintenance or repairs. Usually this will be in the return pipe close to the boiler. However, where a solid ground floor prevents pipes from being run below it, the pipes will drop down from the ceiling void to supply the ground floor radiators. The sections of pipework will remain full of water when the system is drained from the boiler drain cock and will have their own drain cocks, allowing them to be emptied separately. Woodford Plumbers can drain systems.


When refilling the system, make sure all the drain cocks and radiator bleed valves are closed before restoring the water supply to the feed and expansion cistern in the loft. As water flows into the system, air will become trapped in the radiators, so bleed each by opening the bleed valve about half a turn, starting at the bottom of the house and working upwards. Before turning the pump back on, bleed this too.


1). Before doing the system, switch off the boiler, but allow the pump to run for at least 10 minutes to cool the water. Then turn off the pump and close the stop valve in the pipe supplying the feed and expansion cistern. If there is no valve, place a batten across the top of the cistern and tie the ball valve arm to it to prevent the valve from opening. Push one end of the hose onto the outlet of the drain cock. Then, run the hose to an outdoor drain. A Woodford Plumber uses hose.


2). Use an adjustable spanner to open the drain cock, but do not remove the square valve shank completely. When the feed and expansion cistern has emptied work down through the house, opening radiator bleed valves to release any remaining water that is trapped in the radiators.