JSL Plumbing did ours. I got a new Vokera boiler for around £1400. I didn’t do this with JSL, but when I was with my ex, he asked the plumber if we could pay cash to swerve the VAT. He saved us a whack of cash that time. I didn’t think to do it this time round when I got my new boiler. 🤦🏻♀️