Got Fault Code 46 on your brand-new Honeywell 7800 series flame safeguard?
Don’t send it back. Check the configuration jumpers first.
The situation
You replaced an old flame safeguard with a brand-new Honeywell 7800 series unit, reinstalled the same amplifier and purge cards you'd been using, fired up the system... and got an alarm or Fault Code 46 right out of the box.
It looks like a bad part. In almost every case, it isn't. Here's what's actually going on, and how to fix it in a few minutes.
Why this happens
The Honeywell 7800 series looks like a plug-and-play replacement, but every unit has small configuration jumpers on the board (they look like little resistors) hidden under the dust cover or keyboard display. These jumpers tell the flame safeguard how to behave, and every new 7800 series unit ships with the jumpers left intact in their factory default position.
The jumper that causes most of these calls is JR2, the Flame Failure Action jumper. Depending on whether it's left intact or clipped, it sets the unit to one of two behaviors:
- Jumper intact (factory default): Recycle. The system will automatically try to relight after a flame failure.
- Jumper clipped: Lockout. The system shuts down and requires a manual reset before it will try to light again.
Most burner applications are set up for Lockout, which means the JR2 jumper on the old unit was very likely clipped at some point, but the brand-new replacement arrives with it still intact. Swap in the new unit without checking, and the mismatch between the new unit's configuration and your amplifier card/application setup is exactly what triggers Fault Code 46.
⚠️ Important safety consideration
Honeywell only permits the Recycle setting when used with the shorter (1-second) flame failure response time amplifier card. If your system uses the 3-second card, it must be set to Lockout, since too much gas can build up in the chamber to safely allow an automatic relight attempt.
Always verify the requirements for your specific relay module and amplifier before changing jumper settings.
Configuration jumpers (JR1/JR2) on the RM7890 relay module.
How to check it
- Confirm the model number. Pull the old flame safeguard you removed and check its part number against the new one. All 7800 series units look similar, but jumper behavior varies by model, so don't assume they're identical.
- Remove the dust cover (or keyboard display) on both the old and new units to expose the configuration jumpers.
- Compare JR2 (and JR1/JR3, if present) on the old unit to the new one. Was JR2 clipped on the old unit? If so, you'll need to clip it on the new unit to match.
- Match the configuration, not just the part number. Once the jumpers match your application's intended behavior, reinstall and re-fire the system.
The bottom line
Fault Code 46 on a new 7800 series unit almost always comes down to a configuration jumper mismatch, not a defective part. Before you return it, pull the dust cover, check JR2 against your old unit, and adjust as needed.