Honeywell RM7800 lockout 16, no pilot flame on trial: what to check first?
My RM7800 burner control is locking out with Fault 16 during the pilot trial for ignition. I'm not getting a pilot flame, and the main valves never open. What should I 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, but no usable flame signal was detected before the period expired. The main valves will not open when this fault occurs.
Likely causes and checks
1No spark or a weak spark
- Points to it
- The igniter may not be producing a spark, or the spark could be too weak to ignite the pilot gas.
- Check
- Listen for an ignition sound or look for a visible spark through the sight glass. Inspect the electrode tip, insulator, and gap. Check the transformer output and high-voltage lead according to the burner manual.
2Pilot gas not arriving
- Points to it
- Even with a spark, the pilot flame won't establish if pilot gas isn't reaching the burner.
- Check
- Observe if a spark is present but no pilot flame appears. This is especially relevant if the pilot regulator or valve was recently serviced. Read the pilot gas pressure during the trial, confirm the pilot valve opens, and ensure the manual pilot cock is open.
3Detector does not see the pilot
- Points to it
- A pilot flame might be present, but the flame detector isn't registering it, or the signal is too low.
- Check
- If the pilot flame is visible but the flame signal remains below the minimum, measure the flame signal at the test jack during the pilot trial. The minimum reliable flame signal for a 7800 series module is 1.25 Vdc. Clean and re-sight the scanner, or check the flame rod position.
4Amplifier and detector not compatible
- Points to it
- If a flame detector or amplifier was recently replaced, an incompatibility could prevent proper flame detection.
- Check
- Confirm that the plug-in amplifier type matches the detector, as directed by Table 3 in the manual.
Next check: Start by checking for a spark and ensuring pilot gas is flowing, as these are the most common reasons for a 'No Flame in Pilot Trial' fault.
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