A clean line of sight, correct flame target, cool detector, and isolated wiring are the difference between dependable flame detection and nuisance trips.
START HERE
Put the scanner where the flame is strongest.
Target the first third of the flame whenever possible. Where the burner arrangement allows it, sight the intersection of the pilot flame and main flame.
1st 1/3
Highest UV area of the flame
All rates
Highest UV area of the flame
One burner
Highest UV area of the flame
UV scanner body – keep the sight tube clean, cool, and aimed correctly.
Siemens style scanner – verify signal strength after warm-up and during firing changes.
FIELD FLOW
Four checks that prevent most UV scanner issues
01 / AIM
Confirm the sight angle.
Scanner view should include the first third of flame, remain on flame at low and high fire, and avoid seeing adjacent burners.
02 / CLEAN
Keep the path clear.
Dirt, oil vapor, smoke, dust, moisture, and combustion byproducts can weaken UV signal. Use air purge to stop buildup.
03 / COOL
Protect the tube.
Operate below the manufacturer’s high-temperature limit. Add purge cooling, install a heat shield, or move the scanner away from the burner block.
04 / ISOLATE
Separate the wiring.
Run UV detector signal wires in their own conduit. Keep them away from ignition wiring and other 120 Volt lines.
Manual
minimum signal varies by manufacturer – check the scanner/control manual
15 min
warm-up before judging maximum sensitivity
200 ft
maximum UV detector signal-wire length
10,000-20,000 hours
average UV tube life replacement guide
QUICK DIAGNOSTICS
Trouble signs and corrective moves
When the signal is weak
MIXTURE
Check air-gas ratio. UV output falls when the fuel mixture goes off ratio
OPTICS
Clean the view. Verify sight tube, window, and scanner lens are clear; use air purge where buildup is expected.
BOOST
Use quartz help. Use a quartz window for fuel-line sighting or condensation, and a quartz magnifying lens when more UV focus is needed.
When the scanner sees the wrong thing
SPARK
Keep ignition spark out of view. Relocate the electrode or scanner, or reduce the viewing area.
FALSE
Test for false flame. UV scanners can fail in a mode that produces a flame signal all the time; periodic performance testing is required.
BURNER
Limit the field of view. Confirm each detector can see flame only from the burner it is intended to monitor.
Bench and field sensitivity reminders
A properly applied scanner should generate a flame-sensing signal from a 2000 BTU pilot at 3 ft. A match, candle, or lighter flame can be detected from up to 8 ft, and a magnifying lens can significantly increase output when properly applied.
Do not miss these installation details
Do not exceed 200 ft of UV detector signal wiring.
Do not run UV signal wires with ignition wires or other 120 Volt lines
Do not use shielded wire or asbestos wire.
Advanced Thermal Systems – UV scanner setup, inspection, and troubleshooting support. Use with OEM manuals, plant safety procedures, and qualified flame-safeguard service practices