It definitely made a difference (if not fixed it) when I refitted stem properly as per Camilo. I have also a noticed creaking noise so have picked up a new CC S8 to replace existing headset. Thanks for advice.
Yeah, the creaking is probably more likely from the bar/stem interface. If it's actually the headset, it's likely just due to oxidation between the headset press fittings and the frame. Just greasing them would take care of the problem, but you have to remove the headset to do that anyway. Given that operation for a home mechanic, it's probably worth it to throw a new headset in anyway