Do plumbers offer a written warranty? There are fewer manufacturers that produce oil boilers, namely firebird, grant, mistral, warmflow and worcester bosch based on our research. Don has helped me with numerous leaks and other plumbing problems when it's an emergency, he works hard to get us on his schedule promptly we really appreciate his great work ethic and honesty! Need an anual service for your boiler .we can help. Sign up to be the first to hear about our amazing offers, events and competitions!.