The issue with your Triton Topaz electric shower could be due to several factors:
1. **Blocked filter**: A common cause of low pressure alerts, which can be cleaned by a plumber.
2. **Faulty solenoid valve**: This controls water flow and may need replacement.
3. **Worn heat exchanger**: If it's making noises, it could be due to overheating or a malfunction in the heating element.
A plumber can likely inspect and fix minor issues like a blocked filter or solenoid, but if the heating element or other major parts are failing, it may be more cost-effective to replace the unit. While parts for older models can be found online, availability might be limited, and repair costs may add up.