7800 Series troubleshooting answers
12 questions with answers cited from the manufacturer manuals.
- 0Honeywell RM7800 Fault 51: Flame signal too strong during ignition, what to check?
Fault 51 on a Honeywell RM7800 series relay module indicates an untrustworthy flame signal that is too high to be genuine. This often points to ignition interference, an incompatible amplifier, or a failing detector. Sin…
- 0Honeywell RM7800 Fault 33 after shutdown, what to check?
Fault 33 on a Honeywell RM7800 series relay module indicates a pre-ignition interlock issue, specifically that the proof-of-closure switch on the safety shutoff valves did not prove closed when required. This prevents th…
- 0Honeywell RM7800 Fault 32 during modulation, what to check?
Fault 32 on a Honeywell RM7800 series relay module indicates the combustion airflow interlock was not in the required state. This fault can occur during PREPURGE, ignition trials, or RUN. When it trips during modulation …
- 0Honeywell 7800 Fault 28: Pilot Flame Failure
Fault 28 indicates a pilot flame failure on a Honeywell 7800 Series relay module. This occurs during the PILOT IGN (PFEP) stage, 4 or 10 seconds after the pilot valve opens, and prevents the main valves from opening. The…
- 0Honeywell RM7800 Fault 23: Airflow not proven in prepurge, what to check?
Fault 23 on a Honeywell RM7800 series relay module indicates that the combustion airflow interlock did not close during the prepurge cycle. This prevents the furnace from purging and locks out the system before any fuel …
- 0Honeywell RM7800 Fault 20: Low Fire Switch Off, what to check?
Fault 20 on a Honeywell RM7800 series relay module indicates that the low fire switch did not close in time after the prepurge cycle, preventing the burner from lighting at a safe, low input. This fault occurs while the …
- 0Honeywell RM7800 Fault 19: Main Flame Ign. after main valve opens, what to check?
Fault 19 on a Honeywell 7800 Series relay module indicates that the flame signal was lost during the Main Flame Establishing Period (MFEP) or within the first 10 seconds of RUN. This typically means the transition from p…
- 0Honeywell RM7800 Fault 17: Main flame failure in RUN, what to check?
Fault 17 on a Honeywell RM7800 series relay module indicates a main flame failure during the RUN cycle, at least 10 seconds after the main flame was established. This means the burner successfully lit, but the flame sign…
- 0Honeywell RM7800 lockout 16, no pilot flame on trial: what to check first?
Fault 16 on a Honeywell 7800 series relay module indicates that a pilot flame was not proven by the flame detector within the Pilot Flame Establishing Period (PFEP). This means the igniter and pilot valve were energized,…
- 0Honeywell RM7800 Fault 15: Flame detected in standby, what to check?
Fault 15 on a Honeywell RM7800 series relay module indicates that a flame signal was detected during the standby phase, before the burner is supposed to start. This is considered an unsafe condition and causes the module…
- 0Honeywell RM7800 Fault 14 during PREPURGE, what to check?
Fault 14 on a Honeywell RM7800 series relay module indicates that the high fire switch did not close within the allowed time during the PREPURGE cycle. This means the module commanded the firing-rate motor to high fire, …
- 0Honeywell RM7800 Fault 13: Airflow switch on in standby, what to check?
Fault 13 on a Honeywell RM7800 series relay module indicates that the combustion airflow interlock is detected as closed during STANDBY, when the fan should not be running and the switch should be open. This prevents the…