What the work is
Most winter calls here are an igniter, a flame sensor, a pressure switch reading a blocked flue or condensate line, or a limit switch tripping because airflow is restricted. The last one is worth saying plainly: a furnace that keeps shutting off is often not a broken furnace, it is a choked filter or a collapsed duct, and replacing the part does not fix it.
Anything touching combustion gets checked before we leave, whatever we came for.
The parts that fail are a short list and most of them are inexpensive: a hot surface igniter, a flame sensor that has gone dirty enough to stop proving flame, a pressure switch that is doing its job because a flue or a condensate line is blocked, or a limit switch tripping on restricted airflow.
The last two are the ones worth understanding, because the part is not the fault. A pressure switch that will not close is usually telling you something is obstructed. A limit switch that keeps tripping is telling you the furnace cannot move enough air through itself, and the cause is nearly always a filter, a closed-off return, or ductwork that has come apart. Replacing the switch in either case buys you a few weeks.
So the first thing we do on a no-heat call is not order a part. It is find out what the part was reacting to.
What is included
- The failed part named, with the reading behind it
- A combustion and venting check on any gas appliance we open
- The airflow restriction found, if that is what tripped the limit
- The cause behind the failed part, not just the part
- A carbon monoxide check in the space around the appliance
What is not
- Condemning a heat exchanger without showing you what we found
- Work on the gas line beyond the appliance connection unless it is quoted separately
- Replacing a switch that was doing its job, without finding what tripped it
What to ask anyone quoting this, us included
- Did you check airflow before replacing the part?
- Can you show me what you found?
- What did the combustion test read?
- Was the part faulty, or was it responding to something else?
- Did you check the flue and the condensate drain?
