Triton Opal 10.5kW stopped working?

Hi,

I have a Triton Opal 10.5kW shower which has just stopped working. I always keep it on the 2nd heat setting (hottest) but now the water has stopped flowing.

When I turn on the mains power, the lights cycle through all setting and the water flows for 1 second then stops. Then the only light on is the power light.

If I turn the setting to the 1st heat setting (coldest) the water flows fine, constantly, but is not warm.

I am unsure what the problem could be, can anyone help please?