I contracted this company to install a boiler for my newly built garage to heat the garage and house. I had done the bulk of the work, the installation of the things that required certification were still required, propane lines, converting the boiler installing the fresh air intake and flue. I followed whatever suggestions and recommendations he had for the remainder of the installation. He installed three circulation pumps, and the boiler. It was not until much later (5 years) when the boiler kept acting up when it was -47*C. He was unavailable, and did not recommend someone to assist in servicing the boiler which was unable to stay on long enough and produce enough heat to heat the house and garage.
Now onto what was not done correctly, the low water sensor was installed physically wires run into the electrical panel and not connected. The conversion from Natural Gas to Propane was only half complete. The air fuel ratios were not adjusted (A key step in the installation, even in the installation manual) which resulted in an overly acidic residue in the heat exchanger pitting it over the years. It also damaged the igniters, and the exhaust gas temperature sensors (both).
I had another Gas Boiler tech come in, he quickly identified the problems ran a gas analyzer, called Bosch service rep's to help in dialling in the boiler air fuel ratios. Now with air fuel ratios correct, and damaged parts replaced the boiler runs correctly and more efficiently.
In all fairness he was usually available to assist over the years when something went wrong. But I have found that fixes were half complete. His lack of availability to service his customer (me) led me to hire another tech which did not point out things he did wrong but things that were not done correctly.