Mira 147.67

They are probably OK but the first thing would be to makesure that the inlet filters are clear.

The other thing to check is the installation height of theunit although the installation instructions suggest that there should be 80mmbetween the base of the cold water storage thank and the top of the unit, wehave found that due to friction losses etc you probably need about 100mm betweenthe top of the shower head and the base of the tank to ensure no problems

 http://www.mirashowers.co.uk/onlinecatalog/pdf/1088849_w2_d_mira_vigour_thermostatic_power_shower.pdf

Just check that the installation instructions have beenfollowed correctly and if they have then give Mira a ring and the y will sendout an engineer who will repair or replace any parts necessary

It is likely to be a solenoid valve sticking in the on position.

http://www.showerdoc.com/shower-spares/mira/MIRA-PARENT-102-Mira-Event-XS-Manual

Here is the link to the solenoid.

http://www.showerdoc.com/shower-spares/mira/MIRA-453-13-Solenoid-Valve-Assembly-R-components-identified-D