mira sports 10.6kw overheat light on?

My Mira shower was working properly when I switched it off the shower appeared to boil, no water came out,the overheat light came on , a small amount of hot water came out. Now the overheat light stays on on high & medium temps. the water is still cold. Is this the thermostat or heater element.Can it be fixed or is a new shower required.Where should I contact if repair is possible? Thank you