06/17/2026
🚨 2,983 PPM Carbon Monoxide. We shut this down in Oshawa today. 🚨
Called out for a Navien tankless locked out on E110 — Abnormal Air Pressure.
The CO reading on our analyzer: 2,983 ppm.
TSSA B149.1 requires shutdown at 400 ppm. 1,200 ppm is considered immediately life-threatening.
What actually caused this:
After inspection, this wasn't just a dirty filter issue. Two major code violations starved this unit and fouled the heat exchanger over time:
Combustion air intake was never piped outside — This Navien NPE was installed pulling air from the laundry room. Lint, dust, and chemicals from the room got pulled into the burner. Over 8 years, it fouled the heat exchanger and caused incomplete combustion. Navien requires sealed combustion with outdoor air for a reason.
Undersized gas line — The 3/4" CSST supplying this 199,000 BTU unit appears undersized for the run + other appliances. Low gas pressure causes under-firing and massive CO production.
The plugged intake screen we found was a symptom, not the cause. The unit had been running poorly for years.
What we likely prevented: CO poisoning, flame rollout, and catastrophic heat exchanger failure. At 2,983 ppm, you don't get warning signs — you get unconscious.
What MUST be fixed to make it legal and safe:
Pipe the intake outside to code — 2" System 636, 12" separation from exhaust, per Navien + B149.1. No more laundry room air.
Correct the gas supply — Verify sizing, check pressure at high fire. If undersized, run new 1" line. Low gas = deadly CO.
Full heat exchanger service — Clean/inspect for fouling and cracks after years of bad combustion.
Pass a combustion analysis — We don't restart until CO is
