You could do a Level 2 and 3 Diploma in Plumbing and Domestic Heating.
This would teach you some of the skills needed for the job and will help you when applying for a trainee position with a plumbing company.
You'll usually need:
- 2 or more GCSEs at grades 9 to 3 (A* to D) for a level 2 course
- 4 or 5 GCSEs at grades 9 to 4 (A* to C) for a level 3 course