What do I do when my Glowworm Compact 100E pressure is high?

What do I do when my Glowworm Compact 100E pressure is high - red light comes on when I put heating on or when try to get hot water - am novice - do I bleed radiator? This doesn't seem to work - red light now off but pressure still about 4 - no hot water this am - not bothered about heating but really need the water.