Temp. °F/°C
Resist.
Ω – Ohm
Temp. °F/°C
Resist.
Ω – Ohm
70 / 21 11,883 170 / 77 1,403
75 / 24 10,501 175 / 79 1,281
80 / 27 9,299 180 / 82 1,172
85 / 29 8,250 185 / 85 1,073
90 / 35 7,334 190 / 88 983
95 / 35 6,532 195 / 91 903
Table 10 Temperature sensor resistance values - 10K ohms
7.2.2 Fan
Operating power is provided by means of a separate 120 VAC connector (white/black/green). Control of the
fan is provided via a four-lead connector. This connector feeds a PWM control signal (black wire) from the
controller and provides a tachometer signal (white wire) back from the fan. Unplugging the control connector
will cause the fan to go to high speed and trigger a “Blocked Vent Error” within 6 seconds if the boiler is
operating.
7.2.3 Air pressure sensor
The air pressure sensor monitors air flow in the venting system. If airflow through the combustion air intake or
the exhaust vent becomes too restricted for safe operation, the boiler will stop firing, and display a "Fan
Pressure Error". Also, to prevent avoidable Fan Pressure Errors, the system decreases the fan speed if the
reading from the sensor nears the error threshold.
7.2.4 Water pressure sensor
The water pressure sensor ensures that there is adequate pressure in the heating system for safe operation.
The pressure is displayed in PSI as the default. If the system pressure should drop below 8PSI the firing rate
of the boiler is reduced. If the pressure drops to 4PSI or lower, the boiler will not fire.
Check the operation of the sensor by isolating the boiler from its system piping, and close the system fill
valve, and then crack the pressure relief valve. The pressure displayed should reflect declining pressure. If it
remains “fixed”, drain the boiler and replace the sensor, or dislodge any blocking debris from the sensor inlet
channel and reinsert.
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