Modulex Light Commercial Series
CHAPTER 9: Spare Parts Drawings and Lists
OMM-0158_A
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8.8 Burner / Heat Exchanger Cleaning Procedure
Dust and other particulate matter infiltrating into the combustion chamber over time will cause a
decrease of heating efficiency and output due to the buildup of combusted by-products onto the
thermally conductive surfaces. These surfaces must be cleaned from time to time in order to
return the unit to its original specifications for thermal efficiency and heat output.
For detailed cleaning instructions, see section 8.11.
NOTE:
A reduction of the input can be caused by the obstruction of the vent or air intake.
Before cleaning the boiler body sections, check the boiler input and the O
2
percentage (see
Section 4.35).
8.9 Heat And Return Sensor Resistance Values
Nominal resistance differences at a given temperature ratio between the primary and return
heating sensors should be checked periodically by measuring the electrical resistance (ohms)
between the two sensors with a voltmeter. Use the chart below to determine the correct resistance
values at the given temperature ratios.
TABLE 8-2: Resistance Values for Primary and Return Heat Sensors
°F
°C
Resistance (Ω)
32°
0
°
32,755
50°
10
°
20,003
68°
20
°
12,571
86°
30
°
8,112
104°
40
°
5,363
122°
50
°
3,627
140°
60
°
2,504
152°
70
°
1,762
176°
80
°
1,263
194°
90
°
920
EXAMPLE:
At 104 °F (40°C), the nominal resistance is 5,363 Ohm.
At 194 °F (90°C), the nominal resistance is 920 Ohm
