Help the technician see the pattern
If it is safe to observe from the ground, record when the frost appears, which opening is affected, and whether the furnace stops heating. A photo that includes the wall, nearby corner, and both terminations is more useful than one that hides the surroundings.
Note the wind direction if you already know it, without staying outside in dangerous weather to gather evidence. Describe snow buildup separately from frost. Ask the technician to identify the intake and exhaust rather than guessing from which pipe looks wetter.
Do not run repeated heating cycles to create a video. Existing observations are enough to start the service request.
What an explanation should cover
We recommend asking the installer to compare the actual piping and termination with the model and vent-kit instructions. Request an explanation of separation, orientation, nearby obstructions, snow exposure, and the full vent route where relevant.
Ask: “What finding supports the proposed change, and how will you confirm the furnace works correctly afterward?” An answer such as “we usually add an elbow” leaves the model and site questions unresolved.
The technician should also explain whether frost is the cause of the lockout or an observation alongside another fault. Replacing a pressure switch without addressing the conditions it is responding to is not a complete explanation. You deserve to know what was measured and what each recommended repair would resolve.
If weather conditions are absent during the visit, ask what can be checked now, what remains uncertain, and how a recurrence will be handled. Do not treat an uneventful visit on a calm afternoon as proof that the cold-weather pattern is gone.
When the furnace is not heating
Ask about repair timing and whether the household can safely stay in the home while waiting. If reliable heat cannot be restored before conditions become unsuitable, arrange a warm place to stay and professional advice about protecting the property.
Your next action is a site-specific installer follow-up, supported by the weather pattern and safe exterior photos.