Draining a heating system


Open vented systems ONLY

See separate section lower down for sealed systems

Occasionally you’ll got to empty the system to hold out some work there on – maybe to repair a leak or fit another radiator. Before doing so, you want to cut the boiler, disconnect it from the facility supply and switch off the gas supply or, within the case of a solid fuel boiler, make sure that the hearth is out.


Turn off the water system to the feed and expansion tank. If you don’t have a valve for this, or just can’t find it, traffic jams the ball cock with a bit of string round a length of wood across the highest of the cistern.


Using a hose to empty down

Draining the water

Connect a hose to the drain cock which is generally found at rock bottom point within the pipework. Use a jubilee clip to secure it. Place the opposite end of the hose outside to discharge into a gulley.


Open the drain cock employing a pair of pliers and permit the water to start emptying. Now, go around opening the air bleed valves on the upstairs radiators to permit air in to exchange the water. If you don’t, it’s a touch like holding a drinking-straw filled with water together with your finger over the highest end – the water won’t begin. There could also be additional vent points in some systems so check for these also.


Water level in system

As the level of water within the system drops below the peak of the downstairs radiators, you’ll go around doing an equivalent thing for the lower radiators. If the extent hasn’t dropped far enough, water is going to be pushed out of the vents instead of air sucked in.


When no more water comes from the hose, the system should be empty. However, it’s always possible that some water has been airlocked, so lookout.



Close the drain cock and everyone the air bleed valves which were opened to assist drain the system. Turn the water system to the cistern back on.

Order for bleeding radiators

Now, open and bleed the downstairs air bleed valves first, then the upstairs ones. Once all this has been done, the cistern will stop filling because the ballcock closes off the water. the extent of water should be only enough to float the ballcock. quite this, and there’ll not be enough room for expansion because the system heats up. If necessary, adjust the ballcock.


Check any work that you simply have administered to make sure that there are not any leaks, then reconnect the facility supply and switch the gas cock back on. Re light the pilot light following the boiler maker’s instructions and stir up the boiler. Remember to show up the thermostat if needs be.


You’ll got to go around bleeding the air bleed valves again because the system heats up and should got to do that a couple of times over subsequent day or two because the air from the water is driven out.


Finally, once the system is up to temperature, inspect for leaks again. this is often vital as a connection which is watertight when cold may expand and leak when warm.


Draining and refilling sealed heating systems

Because the water in these is struggling, and refilling isn’t as straightforward, you ought to seek the services of a professionally qualified plumber for this.

Edinburgh Central Heating Services offer free estimates and range of skills. A 24-hour emergency plumbing service is also offered. For more information visit www.edinburghcentralheatingservice.com or telephone 0131 5102418