thermostatic shower shut off

My thermostatic shower keeps switching off during showering.
It does not suddenly become too hot, it just simply gives up the ghost.
It makes no difference whether taps are being run in the bathroom ( as I thought that it could be the ballvalve in the loft not replenishing the cylinder fast enough) but the basin taps still work when the shower has switched itself off.
Do you think that it is just a case of replacing the mixer valve? as I cant think of anything else it could be.
The other showers in the flats either side of me are working fine, so I am guessing that this is the case. Any other suggestions?

Shower make and model?

There is no make or model number on it. Took a photo of it to the local merchants, who all said that they did not recognise the make, so I am a bit stuck.

Please post the picture here - you might be surprised at the resources this forum has to offer.