Diamond Mechanical LLC

Diamond Mechanical LLC is a Brentwood heating and cooling company. Its website names 13 towns as its service area, from Portsmouth and Dover to Laconia and Ossipee, and says it offers 24/7 emergency service and free estimates; the company says it has been in business 6 years. Michael L Corbin holds New Hampshire HVAC licence GF1106419, which is active on the state registry. On Google it holds 4.4 stars from 85 ratings, and its BBB grade is B-. A recent customer says Mike installed a new boiler, the process was low pressure, and the work got done quickly once they were ready. A 2026 customer said Mike came the next day about a noisy heating system, the system was drained, 3 valves and the expansion tank were replaced, and the work took less than 2 hours. A 2025 customer said their furnace stopped on a Thursday night, an after-hours message got a reply right away, and by 9am the next morning Mike had their hot water back. A 2024 customer said the company replaced a failed boiler and hot water unit with a new Rinnai system the day after seeing photos of it, and they had heat and hot water by the end of that day. A 2023 customer in Lee said Mike installed two Mitsubishi mini-splits and proposed wall placements that worked better than one of the other bids, though the units went in several months late and they were not kept informed of the delays. A 2026 customer said a warranty furnace replacement took 35 days in the dead of winter, and communication during that time was their only issue. A 2026 customer said furnace service appointments were rescheduled three times in three months with no replies. A 2025 customer said they paid $966, the furnace would not start after a new thermostat and flame sensor went in, and a propane company's tech found the thermostat wired incorrectly; that customer said a promised thermostat refund still had not come 17 days later. A 2025 customer said the original problem was never resolved after multiple paid follow-up visits, and a different provider confirmed it came from Diamond's work. A 2024 customer said a technician forgot to open a valve, leaving water on the basement floor and no hot water, and that the owner offered to come back for a $400 after-hours fee.