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Burner Won't Start?

Purple Flower

If your burner is refusing to start and your Honeywell 7800 Series control is flashing a lockout message, you’re not alone. Combustion systems are complex—and even the smallest issue in the startup sequence can bring everything to a halt.

We’ve broken down the most common messages you’re likely to see and what you can do to fix them. Whether you’re a seasoned tech or just getting familiar with flame safeguard controls, these tips can help you get your system back up and running faster.

Preignition Interlock: These are safety switches that must be closed before the burner can even attempt to start.

What to check:

  • Proof of closure (POC) switch in the gas valve(s)

  • High and low gas pressure switches

  • Safety limits wired to open on fault
A failure here usually means something isn’t reset or is preventing safe startup.

Running Interlock: This group of switches must remain open until the blower starts, and then must close to continue the sequence.

What to check:

  • Airflow switch (make sure the fan is actually running)

  • Auxiliary contacts in the blower starter

If these switches close too soon (or not at all), the controller will lock out.

Pilot Flame Fail: This message means either the pilot flame never lit, or the system couldn’t detect it.


What to check:

  • If the flame is present, your scanner or amplifier might be faulty—try replacing them

  • If the flame isn’t present, check:

    • Spark ignition system
    • Pilot gas supply and valves
No flame = no startup.

Flame Amplifier Type Mismatch: If you’re using an RM7890 controller with a 3-second flame amplifier, but the control is set to recycle on flame failure, you'll get an error.


Fix: Clip the JR2 jumper on the control to switch it to non-recycle mode.

Stuck in Standby: If your controller is stuck in "Standby" and never moves into "Start", it might not be receiving the proper call for heat.


What to check:

  • Is your operating control calling for heat?

  • Are gas pressure switches in their normal position?

  • Are safeties like the low water cutoff or high limits preventing startup?

Burner lockouts can be frustrating—but they’re doing their job: keeping things safe.

When you know what to look for, a 7800 Series fault message can quickly point you to the root cause. Bookmark this post or share it with your team to keep these tips handy.

Need support or want to explore replacement components? Reach out to our Team Today!



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