Hi - moved into a bungalow a year ago. Shower is fine in summer but as soon as weather gets colder, it only get luke warm unless I run the cold tap in the bathroom at the same time.

Can some-one please advise what the problem could be - do I need a new shower?

What's the brand name on the valve? One handle or two knobs? Temperature control valve? More details please. Tom

Hi - it says Gallaxy on the front and G8000s. Has two dials and a separate on/off button

As simple and ridiculous as this may sound, I had a similar problem when I bought my house.. Discovered that, in the shower only, they had crossed the water lines.. My cold" knob controls hot water and vice versa. Aside from that, maybe adjust your water heater setting, but it sounds like your lines might be crossed.. A good way to test it is to just turn on the "cold" water and see if all you get is "hot".