Troubleshooting guide – Modine Manufacturing BAE User Manual
Page 23
2. Yellow Tipping
Yellow tipping of a normally blue flame is caused by insufficient
primary air, and indicated incomplete combustion producing
carbon monoxide, aldehydes, and free carbon (soot). A dirty
orifice or one that is out of line, can also reduce primary air and
cause yellow tipping. Check orifice, clean realign, or replace if
necessary. With propane gas, some yellow tipping is always
present, but is not objectionable.
3. Flashback
Flashback occurs when air-gas mixture ignites inside the
burner to burn near the orifice. Flashback on ignition or during
burner operation usually can be eliminated by reducing
primary air. The burner may also be operating below its rated
capacity. Check input rate and adjust to correct value by
increasing orifice size or manifold gas pressure.
4. Wavering Flames
Drafts across burners may cause flames to waver or appear
unstable. Wavering flames can lead to incomplete combustion
if flames impinge on cool surfaces. Wavering can be caused
by air drafts into the burner compartment or by misalignment
of the burner. Draft-blown flames may indicate a cracked heat
exchanger.
5. Floating Flames
Floating flames are long – do not have well-defined cones, roll
around in the combustion chamber, sometimes completely off
the ports. Usually an aldehyde odor is present to indicate
incomplete combustion. If combustion air supply is reduced
too far, burner flames will float. Often the pilot flame near the
port smothers and goes out. Lack of combustion air causes
burner flames to float. The unit may be overfired so its flue
outlet area may be too small for the increased firing rate.
Check input rate and reduce if necessary. Soot or dust may
be blocking the flue. Check flue and clear any blockage.
Adjust primary air to get rid of yellow tipping that may produce
soot to block flueways. Make sure combustion air inlets are
not blocked.
6. Flame Rollout
Flames rolling out of the combustion air inlets when the burner
is turned on can create a fire hazard, scorch unit finish, burn
wires, or damage controls. Gas in the burner mixer may be
ignited, producing flashback. Flame rollout is a variation of
floating flames, with flames reaching for air outside the
combustion chamber. Basic cause is lack of combustion air
that may be due to overfiring, poor venting, or flue blockage.
Standing Pilot Problem Symptoms and Diagnosis
1. If pilot does not light:
POSSIBLE CAUSES AND REMEDIES
1a. Check that manual gas control (knob or lever) on
combination gas control is in the pilot position.
1b. Bleed air from pilot line. (Use special care in bleeding
propane units.)
1c. If pilot sputters, check pilot line for condensate or other
obstruction.
1d. If pilot flame is feeble or short, check pilot orifice for
cleanliness. Replace if necessary. See page 9 for pilot
flame adjustment.
1e. Be sure thermocouple contact point is clean. If problem
persists, replace thermocouple.
1f. If the above steps do not correct the condition, consult
your local qualified installation and service contractor or
appropriate utility company.
2. If standing pilot does not stay lit:
POSSIBLE CAUSES AND REMEDIES
2a. Check inlet pressure with all units operating, making
certain that there is proper pressure.
2b. Check pipe or tubing size to unit. See Table 1.
2c. Be sure all pilot connections are tight.
2d. Check for excessive drafts.
2e. Check for clogged pilot orifice or pilot line.
2f. Check for leaks around pilot fittings. If leaks cause flame
impingement on thermocouple lead, thermocouple may
become inoperative.
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TROUBLESHOOTING GUIDE
Figure 17
Wavering Flame or Misalignment
Figure 18
Floating Flame Condition
GOOD
BAD
Figure 19
Flame Rollout Appearance