Worcester Bosch 240 - reset switch problem?

Hi, I am in need of some help, I have a problem with my Worcester Bosch 240 boiler. I have already replaced the diaghram a couple of times, and the last time decided to change the complete diverter valve just in case this was causing my problem.

The Problem is that when running my hot water, (normally when running a bath), My reset switch trips sometimes once and at other times 15 times in the duration of my bath being filled.

Somebody suggested air lock in the heat exchanger (red container) which I have bled and with old diverter valve, there was some air. Now with the new assembly there isn't any air or anything coming from this valve.

Please can anybody shed some light on this problem.

Many thanks

Cliff