I didn't deal with Peter, but with someone else from ThermTech (possibly Steve?). I have to give kudos to ThermTech, because their rep came to my home in the middle of a snowstorm to check out my Lennox G26 furnace. My furnace was no longer automatically turning on consistently and so my house was 14 degrees. Sometimes if I turned off the power and turned it back again it would work, but unfortunately it wasn't reliable. Eventually it would just stay off and not come back on, until I flipped the power switch off and on again several times.
ThermTech's tech came over in the peak of the snowstorm. He was polite and checked out the furnace. He cleaned out the hoses and checked the connections. He wasn't entirely sure what was wrong, but luckily the furnace worked after that. He charged me the usual diagnosis fee (which was less than $100), but nothing extra. However, the next morning the furnace didn't come on. ThermTech came back to rediagnose it for no charge. I asked about the ignition control module because I had read online that it was a known problem with these Lennox units, but the ThermTech tech assured me it was working fine. Again the unit worked after he replaced one part but again it stopped working the next morning. I believe it was after another visit he essentially gave up on the unit. His advice was just to turn up the heat on the thermostat, which of course didn't solve the problem.
I called another company, and basically over the phone, he diagnosed the likely problem to be the ignition control unit, which the ThermTech tech had assured me was fine. The rep from the other company came over, confirmed the Johnson Controls Intermittent Pilot Ignition Control unit to be the problem, and replaced the unit. My furnace has worked perfectly since then.
I have given ThermTech a 6 because they tried hard and although came to visit several times (including once in the middle of a big snowstorm) and even did some work changing one part (and changing it back to the old one after it was clear it didn't solve the problem), but they only charged me the initial diagnosis fee which was less than $100. However, they lost 4 points from me because they were unable to diagnose the problem, even after I asked specifically about the problem part.
I also note that the other reviews here are universally positive, about Peter. I did not deal with Peter and that may be the problem. Peter was away when I called ThermTech, so I got somebody else. Overall ThermTech gets a 6 out of 10 for me for trying hard and not charging me much, but ultimately failing to solve the problem.