Water Pressure Sensors; Hi-Limit Switch & Ignition Module - IBC VFC 15-150 Manual

Air pressure sensor mounting
Do not blow into sensor ports
Return water pressure sensor
Fenwal ignition module - Microamp
(μA) test points are shown at top
right corner of module (above red
L.E.D.)
5-4
VFC 15-150 - VFC 45-225 MODULATING GAS BOILERS
Next, confirm that the circuit is properly powered. The supply voltage to the
sensor should be 13.8 VdC; to check, the simplest technique is to measure the
circuit on the face of the controller circuit board (vs. an attempt to splice into the
harness / connectors). see above for a presentation of the measurement points.
Finally, to measure the sensor output, connect a dC volt meter between points
"J501-33" (located on the footprint of the 34 pin connector – immediately below
the right leg of the lCd display - second pin from bottom right) and gnd (see
above). With the fan off, the measure should read 0.5VdC. With a Fan Pressure
of approx. 300, the meter will read 1.5v (approx.). note:- this component is a
sensor, not a switch; do not over-pressurize by blowing into the air reference
lines. Maximum pressure capacity is 40" w.c. @ 20 C but only 10" w.c. @ 5C.

5.2.4 Water Pressure Sensors

go to the Advanced Diagnostics screen, and check the top 2 display lines —
inlet Pressure and outlet Pressure. With the pumps at rest and system pressure
of 12.5 psi, the Inlet Pressure and Outlet Pressure sensor values should read
235 +/- 5. of the two, while at rest, the inlet normally reads 1 – 2 points higher,
reflecting the extra 2' of water column. The third displayed line Delta Pressure will
normally indicate a value of approx. 20 with pump in operation. the location of
the boiler pump will determine the movement of valid sensor values; in general,
inlet pressure will increase while the outlet will decrease when the pump starts.
Check operation of both sensors by isolating the boiler from its system piping,
closing the system fill valve then cracking the pressure relief valve; both signals
should reflect declining pressure. If one or both remain "fixed", drain boiler and
replace sensor(s), or dislodge any blocking debris from sensor inlet channel
and reinsert. to remove a red-coloured "502" sensor, it is necessary to release
a stainless steel retaining clip at the base of the unit (see Section 6.1 Parts
Diagrams, part #65). Before refilling system, ensure the 502 sensor retainer clips
are properly re-installed. the black "505" sensors are threaded and do not use
the retainer clip system.
5.2.5 Hi-Limit Switch (water and vent)
Check resistance between leads. if resistance is very low, temperature should
be acceptable. if resistance is very high, temperature should be out of bounds.
a simple means of checking whether a high limit switch is open is by measuring
the aC voltage across the device. if the reading is 24 VaC the switch is open. if a
0VaC reading is shown, it is closed. neVer connect an ohm-meter or continuity
checker across a live circuit.
5.2.6 Ignition Module
there are two approved ignition modules - Fenwal (grey) and Capable Controls
(white). each have a red led lamp providing the following signals: Fenwal – 1
rapid flash on 1st entering Pre-purge, 3 rapid flashes upon Failure to Ignite After 3
Attempts; the Capable Controls module provides a single flash at the start of each
Purge and Interpurge cycle, continuous rapid flashes during the 4 second spark
interval, solid illumination following successful ignition until burner shutdown, and
a slow on/off cycle with a 3-try failure.
Flame current can be monitored on the Fenwal. Connect an electrical test
meter - set to read Microamps (symbol μA) to the two test pins at the top right of
the ignition module. recycle the boiler so it enters another trial for ignition and
monitor the flame current reading. When the burner ignites, a steady reading of
INSTALLATION AND OPERATION INSTRUCTIONS