Burner / Heat Exchanger Cleaning Procedure; Heat And Return Sensor Resistance Values - Watts AERCO EXT Installation, Operation & Maintenance Manual

Modulex EXT Commercial Series
CHAPTER 8: Maintenance Schedule

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 combustion 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
section 4.33).

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°
50° 10°
68° 20°
86° 30°
104° 40°
122° 50°
140° 60°
152° 70°
176° 80°
194° 90°
Example: At 104 °F (40°C), the nominal resistance is 5,363 Ohm. At 194 °F (90°C), the nominal
resistance is 920 Ohm
OMM-0160_A • DRAFT
32,755
20,003
12,571
8,112
5,363
3,627
2,504
1,762
1,263
920
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percentage (see
2
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