Filters could be blocked and / or hot or cold supply or both may be air locked:
1. Unless you are pretty clued up on plumbing and electrics, get someone in to check and clean the filters. Otherwise, down load the Triton instructions, make absolutely sure you isolate the shower electrically and turn off the hot and cold water supplies, then remove, clean and replace filters per instructions. Its not difficult but you must observe safety precautions, and replace the cover properly afterwards.
2. Unscrew shower head, set to middle heat, turn shower on and suck hard and quickly through the shower hose. Hard and fast is the way to do it, as the shower will be damaged if you run it without water. If you have it, you can reinstall the commissioning link (see instructions) and do it that way.