Hi there, I have a Honeywell V4073 sundial Y plan 3 position diverter valve and I need to see if it is working correctly. To start with the hot water is scolding, so I replaced the tank stat but it made no difference and when I turn the CH off at the main control panel the radiators stay on. so I think I have narrowed it down to the valve. I have removed the powerhead and the valve appears to move freely.I want to know if there is a simple (laymans) test that can be done before I start replacing bits unnecessarily.