ideal combi 24

Look for a drain off valve on one of the rads, make sure the boilers off and cooled down

 

Yep as above turn the power off the boiler at the fixed spur, find the drain off point on a downstairs radiator, usually near a door, fit hosepipe and drain. You will of course have to open the bleed nipples to allow the air in start upstairs first. Before refilling add an inhibitor to the system close all the vents, ensure the new valves are open and refill using the filling link, venting from downstairs to up. Take the pressure to 1 bar, turn on the heating allow it to settle, (you will hear some air and water movement). Vent the rads again getting the last of the air out. Check the system pressure needs to between 1 to 1.5 bar when hot.

One little tip if you cannot find a drain off on the system get yourself one of those DIY washing machine taps the type that cut into the pipe. Fit that below a downstairs radiator attach a hose to it and drain down, you can then remove it, cut in a drain point using a compression tee if your not confident soldering and you will have a drain cock ready for future use.