Anthony and jake came out and unclogged my drain! did a great job , fast , and knowledgeable! Expect to pay between £, and £, or more, depending on the complexity of the installation, for a back boiler to combi conversion job. Are you planning on installing a new central heating system for your home? Some local governments also require a fire inspection before heating system replacements the fees for these are dependent on the size of the boiler and tend to run.