I had replaced a regulator for a an elderly female client changing from standing pilot to intermittent due to her hard time in relighting pilot. As i tried it myself unit blows out the pilot during start-up what appeared to me was an excessive gas build-up prior to lighting of the main burner. During this time, I also noted metal chips accumulation at the bottom of the combustion chambers. I recon the unit was at least 20 plus years old, I cleaned up the shavings and showed it to my client, also informing her of the possibility of furnace wall thinning. Also I took out the burner pipes and tapped to get rid of loose iron oxide, reassembled and replaced the gas valve. Operated the unit on and off multiple times, blow back was intermittent, flames appeared blueish-white, intermittent yellowish flame and pressure sounds normal. T'stat kick it on/off few times, I close the door and she was happy to have heating.
Fast-forward today, I received a call from her asking me why her gas bill went up so high. She claimed she had the gas co to check for leak and they determined no leak was found. I will be checking the unit tomorrow, I'm asking the salty's out here for ideas, concern and possible solution...many thanks.