Auto reset light - stuck on cold water ?

Hi, we have a Galaxy Aqua3000 10.5kw shower, Auto reset light on and just runs cold water. Shower head is not blocked and Galaxy advise us to check the filter, we have took the front panel off and cannot see any filters do you know where they could be, or are there any obvious ways to fix this problem or to ensure we have checked everything that we need before we call out the Galaxy Engineer who will charge us if it is not a manufacturer fault.
Thanks