Burnham CHG225 - Manual (Page 42)

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Figure 10.2: Gas Valve Detail
11) Perform a combustion test. On horizontally vented units, the sample probe may be inserted into the terminal.
If this is not possible, and if no sample tap is present in the vent system, remove the flue temperature sensor
and insert the analyzer probe in the sensor opening. On the CHG150 and CHG225 the flue temperature probe
is located behind the lower vestibule door. For the boiler to operate, this sensor will need to be temporarily
connected outside of the boiler. If it is removed, be sure to return the flue gas temperature sensor to its original
position after combustion testing is complete.
Check CO2 (or O2) and CO at both high and low fire. The boiler may be temporarily locked into high or low
fire for 15 minutes as follows:
a) To lock the boiler in high fire, simultaneously press and hold the “Mode” button and “+“ button until
the display flashes “H”, indicating that the boiler has been driven to high fire. After this happens, allow the
boiler to operate for approximately 5 minutes before taking combustion readings.
b) To lock the boiler in low fire, simultaneously press and hold the “Mode” button and “-“ button until
the display flashes “L”, indicating that the boiler has been driven to low fire. After this happens, allow
the boiler to operate for approximately 5 minutes before taking combustion readings.
At both high and low fire, CO readings should be less than 75 PPM. Typical CO2 readings are shown in Table
10.3.
Normal modulation of the boiler should return 15 minutes after the boiler is locked in high or low fire.
Table 10.3: Typical CO2/O2 Combustion readings range
Model Fuel %CO2 %O2
CHG150 Natural Gas 8.2 6.3
CHG225 Natural Gas 8.7 5.4
CHG150 Propane NA NA
CHG225 Propane 10.2 5.4
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