I’m looking to drain my central heating system just to do a little pipe work. Normally I would drain the system as a whole from the drain point on the radiator by the front door. I don’t mind doing that again, but I did wonder if turning the radiators off and draining just the pipework would suffice, then I noticed the 2 valves circled on the boiler on the ch flow and return pipes. I know it may sound daft, but would closing these keep the water in the boiler too meaning even less water to drain? My only concern is that they've not been used in the 13 years we’ve lived at the house, so I’d hate to break them or them not reopen. I know it’s lazy and I’ve got to the drain the system again soon to fit a new radiator but for this brief bit of pipework I need to do I did hope I could keep it to a minimum.