Hello, I am having heat inside my cabin. When the air is switched to the cold blue line no hot air from the duct. But the radiator inside the cabin is getting hot and causing hot feeling at the footwell area. While checking the hot water hoses I noticed that the control valve is missing (picture below). If I don't want to replace by a new one, can I simply install a small ball valve on the hose to prevent hot water from reaching the radiator during summer season, and in winter I reopen the valve to allow hot water from circulating again??
please advise.