INSTALLATION AND OPERATION INSTRUCTIONS
5-4
SL 20-115 MODULATING GAS BOILER
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 previous page 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 Sensor
go to the
Advanced Diagnostics
screen, and check the top display line — inlet
Pressure. With the pumps at rest and system pressure of 12.5 psi, the
Inlet
Pressure
sensor value should read 235 +/- 5.
Check operation of the sensor by isolating the boiler from its system piping,
closing the system fill valve then cracking the pressure relief valve; the signal
should reflect declining pressure. If it remains “fixed”, drain boiler and replace
sensor, or dislodge any blocking debris from sensor inlet channel and reinsert.
5.2.5 Hi-Limit Switches (water and UvHL)
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 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 2-7 Microamps should be
measured by your meter. the control will lock
out if the reading drops below 0.7 Microamps.
(see Section 5.3.1 - “Control Module - Maximum
ignition trials error”, and Section 5.3.2 - “Ignition
problems”). For conversion from Fenwal to the
Capable Control, specify IBC part# 240-049 –
that provides the module plus added wire lead
and instructions. Flame current measurement is
not possible on Capable Controls module.
Do not blow into sensor ports
Air pressure sensor
Water pressure sensor
Upper Vessel High Limit (UVHL)
Water temperature high limit switch
Fenwal ignition module -
Microamp (μA) test points are
shown at top left corner of
module (beside red L.E.D.)
