I installed a Heatilator Caliber, natural gas fireplace, model CNXT4236 a couple of years ago in my basement. When the outside temperature gets below 32°F or so I have to heat the area where all of the electrical and piping is below the firebox to get it to light. The pilot comes on and the sensor glows red but the burner won't come on. If I blow an electric heater in the area for a few minutes it lights fine and continues to work fine until it's been off for several hours.

  • Does this happen every time the outside temperature is below freezing, or only some of the time?
    – Tester101
    Jan 3, 2013 at 12:16
  • Could it be a down draft? I'm having the same problem. -25C here!
    – Michael
    Jan 14, 2020 at 2:18
  • I have the exact same problem, -25C here now and mysteriously the fireplace wouldn't lite. Also the pilot looked lower that usual too, then would go out. Re-lighting it, it would be full size for a bit, then dwindle. I tried heating the valve like you did and that totally fixed it, just like it did for you. I bet there's something about cold gas in a cold valve. My thermal camera only showed everything at +18C, so not overly cold...
    – Michael
    Jan 14, 2020 at 3:29

3 Answers 3


From the Manual, one of these two solutions sounds most likely:

Verify all connections to wiring diagram in manual. Verify connections underneath pilot assembly are tight. Verify flame sense or igniter wires are not grounding out to metal chassis, pilot burner, pilot enclosure or screen if present, or any other metal object.


With fixed glass assembly in place, verify that flame is engulfing flame-sensing rod on left side of pilot hood. Flamesensing rod should glow shortly after ignition. With a multimeter, verify that current in series between module and sense lead is at least 0.14 microamps. Verify correct pilot orifice is installed and gas inlet is set to pressure specifications. Polish flame-sensing rod with fine steel wool to remove any contaminants that may have accumulated on flame-sensing rod.

The fact that it occurs only when cold could mean a poor electrical connection (metal expands when heated which results in a better connection), or the thermocouple is not properly in the flame (maybe by such a small distance that the room heat allows it to get to the proper voltage).


If the ignition system tested fine, maybe install a moisture trap before the appliance.

  • When you say "moisture trap", are you referring to a short downward stub leg of piping? (In North America, we often call those "drip legs") Feb 10, 2021 at 2:38

It's due to an extreme cold draft in your vent - heavy cold air can smother the pilot. If you have access to the vent make sure it is free os frost, snow and ice and try again .... if you have the ability to get a secondary flame / heat source into the fireplace to warm up the draft tat may help as w

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