IBC SL 35-199

5-9
TROUBLESHOOTING
SL 35-199, SL 45-260 MODULATING GAS BOILERS
5.3.3 Cycling Problems
SYMPTOM DIAGNOSIS REMEDY
RAPID CYCLING Improper values
entered via keypad.
Check load maximum temps are above target
temps, by 1/2 of the selected boiler differential.
Ensure boiler differential is OK (16-30°F is
generally adequate)
Excess Condensate in
venting.
Check venting slopes on horizontal runs. Look
for sags.
Obstruction in
condensate trap.
Inspect and clean condensate trap.
Improper vent length
or improper slope to
vent.
Check venting. Compare vent length and
diameter to Table 3: Maximum Venting.
Incorrect settings or
defective thermostat.
Check operation. Refer to manufacturer’s
instructions. Check setting with ammeter.
Air in system or
marginal water ow.
Bleed/purgesystemasrequired.Conrm
adequate pump size and temp rise in HX
Slow combustion air
blower.
Check that CO
2
leveliswithinspecication.
Dirty burner/heat
exchanger.
Check pressure drop.
Low water ow due to
improper piping.
Refer to recommended piping in Section 1.6
Low water ow due to
undersized pump.
Check manufacturer’s rating charts/check
temperature differential across heat exchanger.
Low water ow due to
restrictions in water
pipe.
Check temperature differential across zone/heat
exchanger.
Low radiation. Check actual amount of radiation per zone and
refer to manufacturer’s rating tables.
Unit over-red. Clock gas meter/check gas pressure with
manometer/ check CO
2
level.
Unit Oversized. Check load calculation vs. min. boiler output.
Improperly set or
defective operating/
safety controls.
Check operation with ohmmeter/voltmeter.