The purpose of a peppermint test is to determine if the plumbing drains/vents are leaking. If you get ANY PEPPERMINT odor, there are leaks. I don't know how they test for leaks in your area but in our area, new construction plumbing is tested by plugging the main sewer pipe, plugging or capping all drains and vents except for the highest vent in the house and then filling the entire system with water until water overflows the highest vent. Allowed to stay full for several hours, any leaks and/or non-welded joints will reveal themselves in short order. You stated that you immediately smelled peppermint when that test was done and that puts the building in the liability department. He had the house built and plumbing drain leaks are not allowed. Period, end of story. You need to have a conversation with that chap and let him know that the house doesn't meet minimum plumbing standards. If he/she resists, you may need to contact your local health authority and be prepared to move out until the problem is resolved. I strongly suspect, as others have already stated, that your odor issue is plumbing related, not combustion related. This is a serious health issue and potentially a life threatening issue (sewer gasses are explosive). You need to take definitive action and the sooner the better.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!