mira sports max problem?

my mira sport max is 18mnths old and has developed an intermittent problem. when switched on by pressing top button on the unit, the red light dims and there is a two or three second delay before it begins. it will not turn off at all and in order to stop it i must pull the cord switch on the isolator box.

this is urgent cos it is a rental property and i have guests saturday. i need a repair and i am willing to give it a go, but i dont know which parts to replace.

can anyone help?

thanks