INSTALLATION AND OPERATION INSTRUCTIONS
5-4
SL 35-199, SL 45-260 MODULATING GAS BOILERS
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) Standard and Capable
Controls (white) Alternate. 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 DC 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 DC 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”).
Upper Vessel High Limit (UVHL)
Water temperature high limit switch
Fenwal ignition module - DC
Microamp (μA) test points are
shown at top left corner of module
(beside red L.E.D.)
Summary of Contents for SL 35-199
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