Originally Posted by puddle

if you can hear the valve 'kick in' when on hot water mode,valve probably wired incorrectly as no power to valve motor gives you hot water only
A quick test for you to do is turn power off to system this will make sure valve in hot water position ,then remove valve head from body ,then turn power on to allow boiler and pump to operate,hot water should get hot as valve in correct position ,if so wire valve correctly,if rads get hot,valve wrong way round,is nothing gets hot possible air lock