8.3.4 Cycling issues
Cycling issues
Issue Diagnosis Fix
Rapid
Cycling
Improper values entered via
keypad.
Check load maximum temps are above target temps, by ½
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.
Incorrect settings or
defective thermostat.
Check operation. Refer to manufacturer’s instructions.
Check setting with ammeter.
Air in system or marginal
water flow.
Bleed/purge system as required. Confirm adequate pump
size and temp rise in the heat exchanger.
Slow combustion air blower. Check that CO
2
level is within specification.
Dirty burner/heat
exchanger.
Check pressure drop.
Low water flow due to
improper piping.
Refer to recommended piping for the respective boiler
model.
Low water flow due to
undersized pump.
Check manufacturer’s rating charts/check temperature
differential across heat exchanger.
Low water flow 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.
Appliance over-fired. Clock gas meter/check gas pressure with manometer/
check CO
2
level.
Appliance Oversized. Check load calculation vs. minimum boiler output.
Improperly set or defective
controls.
Check operation with ohmmeter/voltmeter.
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