Why does the water temperature from my mixer shower sometimes fluctuate from very cold to very hot?

your mixer shower is a manual type and not thermostatic. Common reasons for this symptom are:

• Water being drawn off at other outlets or appliances is adversely affecting the pressure and flow to the shower.
• Shower plumbed in wrong i.e. cold mains and gravity-fed hot water.  

We always recommend thermostatic mixer showers.