National Oilheat Research Alliance 51
ter vents must remove the air from the system
piping. This will cause the heat emitters closest
to the main to heat first and the furthest heat
emitters will either under-heat or may not heat
at all.
System/Boiler Overfilling or
Flooding
Overfilling can be caused by:
• A replacement boiler that is significantly
smaller than the one it replaced. If the boiler
doesn’t have enough storage water volume it
can lead to unnecessary feeder operation. A
boiler feed system may be necessary.
• The boiler feed rate may be too fast, causing
the boiler water level to collapse when
feeding. Check to be sure that the pump
discharge pressure or feeder make up rate is no
higher than necessary. In some cases an electronic
water feeder may be needed to control
the feed rate.
• The boiler may be “foaming” due to poor
water quality or incorrect near boiler piping.
Either of these conditions can cause water carryover
to the system and premature low water
conditions.
Excessive boiler water level
bounce
Water level movement is normal in all steam
systems. When the water level bounces excessively
(from top to bottom of gauge glass)
check for:
• Incorrect near boiler piping.
• Dirty boiler water. If the water is dirty
clean and skim it according to the manufac-
turer’s instructions.
• High pH.
• Excessive feed rates from the pump or
feeder.
Rapid cycling
If the burner is cycling rapidly, check for:
• Improper near boiler piping.
• Low water cutoff cycling due to water level
bounce.
• Proper operation of air vents or traps.
• Improperly adjusted differential in the
pressure control.
• Improperly adjusted thermostat heat
“System flooding often occurs anticipator.
because the boiler steaming time
is shorter than the time it takes
for condensate from the system to
return to the boiler. As the boiler
water level drops, the feeder adds
water to keep the boiler running
and when the condensate returns
the boiler floods.”
Most systems will foam
excessively when the pH is
higher than 9.5
If the system is operating at
2 psig or less, the pressure control
differential should be set to a
minimum of 1 to 1.5 difference
between cut-out and cut-in.