Honeywell 7800 Series Burner Control (RM7800 / RM7840)
Honeywell 7800 Series Burner Control (RM7800 / RM7840) *Airflow Switch*: Airflow Switch
The control did not get proof of proper combustion airflow during the prepurge cycle, which causes the burner control to fault.
Safety first. This code involves a gas, flame or electrical hazard. Do not keep resetting it. Leave burner, gas train and high voltage work to a qualified technician. WERCS answers 24/7 at (877) 489-3727.
- Code
- *Airflow Switch*
- Name
- Airflow Switch
- Controller
- Honeywell 7800 Series Burner Control (RM7800 / RM7840)
- Type
- General fault
- What it does
- Lockout: the control shuts down and stays off until it is reset
- Risk
- RED Specialist territory
- Reset
- Needs a manual reset
- Source
- The manufacturer's manual (subscribers see which manual and page)
Updated July 22, 2026
How to fix it
Subscribers get:
- What to do next, in plain words
- Which manufacturer manual it comes from, linked
- The 4 common causes listed for this code
- Booking a live video call with Ben, a master booth technician ($250/hr, paid per call)
Questions about this code
What does Honeywell 7800 Series Burner Control (RM7800 / RM7840) *Airflow Switch* mean?
The control did not get proof of proper combustion airflow during the prepurge cycle, which causes the burner control to fault.
Is Honeywell 7800 Series Burner Control (RM7800 / RM7840) *Airflow Switch* dangerous?
It is graded red, specialist territory: it involves a burner, gas, flame or safety lockout, so leave the repair to a qualified technician.
How do I fix Honeywell 7800 Series Burner Control (RM7800 / RM7840) *Airflow Switch*?
The manual's fix and the step by step check for this code are in WERCS Diagnose, plans from $49 a month. For help right now, WERCS answers 24/7 at (877) 489-3727.
Other Honeywell 7800 Series Burner Control (RM7800 / RM7840) codes
*Running ILK* · Running ILK*High Fire Sw.* · High Fire Sw.*Flame Detected* · Flame Detected*Main Flame Fail* · Main Flame Fail*Preignition ILK* · Preignition ILK*Low Fire Sw. Off* · Low Fire Sw. Off*Pilot Flame Fail* · Pilot Flame Fail
All 8 Honeywell 7800 Series Burner Control (RM7800 / RM7840) codes · Every fault code