Installation and Operation Manual
TFTN 085-199
36
Adjustments to the
Offset Screw
may only be made by a qualified gas technician using a calibrated
combustion analyzer capable of measuring CO
2
and CO, and only with the burner operating at Min
Power (10%). Attempting to set the Offset Screw while the burner is operating above Min Power
will result in incorrect combustion and may lead to burner damage or excessive CO.
Gas Line Pressure Test
The boiler gas valve is equipped with a line pressure test port; see Figures 9-2 & 9-3. Use the following procedure to measure
the gas line pressure to the boiler to ensure it falls within the range given in Table 9-1:
1.
Turn the supply of gas to the boiler off.
2.
Open the bleed screw of the line pressure test port approximately 1-1/2 turns. This port is directly connected to the
gas line feeding the boiler. See Figures 9-2 & 9-3.
3.
Force 1/4
ID tubing over the housing of the line pressure test port; install the other end of the tubing to an appropriate
line pressure test gauge or manometer. Ensure both ends of the tubing make a tight connection.
4.
Open the supply of gas to the boiler and check for gas leaks.
5.
Observe the line pressure under static conditions and compare it to Table 9-1. The pressure will be greatest under
static conditions.
6.
With all other gas appliances in the application running, operate the burner at Max Power (100%) and compare the
observed line pressure with Table 9-1. The pressure will be lowest during the maximum flow of gas.
7.
Adjust the gas line pressure to ensure the parameters in Table 9-1 are attained under all conditions. If possible, adjust
the line pressure to middle of the range listed in Table 9-1, while the unit is operating at Max Power (100%).
8.
Continue observing the gas line pressure until the completion of the combustion analyses in case adjustments need to
be made.
9.
Complete pressure testing, and then return the bleed screw of the Line Pressure Test Port to the closed position.
The line pressure is a function of the gas supply and is affected solely by field provided parameters
such as line size and regulator settings. Under no circumstances can the boiler gas valve influence
or be used to adjust the gas line pressure.
Failure to close the bleed screw of the Line Pressure Test Port will cause a severe leakage of gas,
resulting in a fire or explosion causing property damage, serious injury or death.
Table 9-1 Combustion Parameters and Gas Line Pressure
Model
Natural Gas
Propane
CO
2
CO
Line Pressure
CO
2
CO
Line Pressure
Max Power
(100%)
Min Power
(10%)
Max Power
(100%)
Min Power
(10%)
85-199
8.7-10.0%
8.5-9.8%
<175ppm 3.5-
10.5” WC
9.7-11.0%
9.5-10.8% <175ppm
8-
13” WC
285-399
8.9-10.0%
8.5-9.6%
<175ppm 3.5-
10.5” WC
9.9-11.0%
9.5-10.6% <175ppm
8-
13” WC
Notes
:
1
TFTN085-199 models
–
the CO
2
at Min Power (10%) must be set lower than the CO
2
at Max Power (100%) by 0.2-1.0%
2
TFTN285-399 models
–
the CO
2
at Min Power (10%) must be set lower than the CO
2
at Max Power (100%) by 0.4-0.8%
