LAARS U.H.E. - Service Manual - Manual (Page 18)

LAARS Heating Systems Page 18
Does inlet gas pressure
drop more than 2" W.C.
during burner ignition?
Adjust gas
supply regulator
Inadequately
sized regulator.
Y
N
N
Y
N
Y
N
IGNITION MODULE
Verify Minimum Gas Supply Piping Requirements of:
Minimum 1" NPT for UHE100T399, all others use ¾"
NPT. (Schedule 40 black Iron Pipe recommended).
Reconfigure gas
supply piping
Y
Observe burner operation through the sight glass located on the combustion insert mounting flange. Normal burner operation
should ignite smoothly, without evidence of coughing or huffing upon ignition. The burner flame should be a blue flame near the
burner surface in a uniform flame pattern. Occasional yellow or white streaks are normal.
Inlet gas
pressure tap
Venturi
adjustment
Is igniter resistance
less than 150 Ohms
(cold)?
(see check igniter
illustration)
Refer to ignition module illustration below,
is there 120VAC across terminals
P6(1) and P6(2)?
(Note: Igniter LED must be lit during this check).
Y
N
Replace
hot surface igniter.
(see page 30)
Replace ignition module.
(see page 34)
N
Y
Do you see the igniter
glowing through burner
site glass during the
warm up period?
Proceed to next page
With manometer, check inlet
gas pressure. Is it stable
between 7" & 14" W.C. static?
(heater not running)
(see illustrations at right)
Is gas supply pressure
regulator adjustable to
maintain proper and
stable setting?
Y
N
Volt meter set to
OHM setting
Meter probe
Hot surface
igniter
CHECK IGNITER
RESISTANCE
WARNING
120 volt potential
exposure. Use caution
making voltage checks to
avoid personal injury.
WARNING
Removing screw from
inlet gas pressure tap will
immediately allow gas to
flow from pressure tap.
Note: On higher input models using metal fiber mesh burner (serial
number “CK” and later) a red glow from the burner surface is normal.
18