Question about Philips Sonicare Sonicare DiamondClean

You're not doing anything wrong. The toothbrushes are somewhat susceptible to damage. If you still have a warranty on it, send it in and you'll get a new one (we've already had to do this). We haven't had this exact problem yet, but we have had extreme noise and reduced performance. As long as this occurs during the warranty period, there are no problems with repairing/replacing. Nevertheless, the toothbrush is one of the best, as my healthy teeth, my DH and the dentist have confirmed time and again.

The toothbrush recognises the attached brush head (with chip, so-called intelligent brush head) and changes the mode accordingly. If you change the mode manually, the newly set mode should be retained the next time you brush. However, if you remove and replace the brush head each time, the toothbrush may switch modes again (I have never tried this). Personally, I rinse the brush with water after use and dry it lightly. I clean the surface between the brush head and toothbrush every fortnight, only then do I remove the brush head. The "Gum Care" mode is presumably intended for gum care and not for permanent use, so it is possible that it is not set permanently. Whether this independent changeover is perceived as practical or tedious depends on the user.