Dunkirk Excelsior EXB Series - Manual (Page 40)

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16 - OPERATING THE BOILER - SYSTEM START-UP
16.6 Activating Thermal Pre-Purge (optional)
Activation of this feature is not recommended for boilers
with tankless coils.
• Limit has thermal pre-purge feature to maximize
efficiency. When activated, control will purge higher
boiler temperatures down to 135°F at start of any
thermostat call and supply latent energy in boiler to
heating zone calling.
• During purge cycle, display will indicate PUR.
• If heat is not sufficient to satisfy thermostat, control will
energize burner.
• Feature works with single and multi-zone heating
systems utilizing circulators or zone valves. No change
in wiring is needed.
To Activate Thermal Pre-Purge
1. Push and hold TEST/SETTINGS button for 20 seconds.
2. Display will read PURR On.
3. To deactivate feature, push and hold button a second
time for 20 seconds.
4. Display will read PURR OFF.
16.7 Control Action On System Start-Up
At initial start-up, with economy feature active, control
establishes 145°F target temperature. To test high limit
shut-off function, economy dial must be turned to off.
Once tested, restore economy setting.
If heating demand is high, target will increase over time to
satisfy heat load.
To reduce potential for condensing, control will allow boiler
to heat to 120°F prior to energizing the circulator.
16.8 How Thermal Targeting Works
Thermal targeting technology analyzes thermostat activity
and continually evaluates how much heat the house
requires.
When it is very cold outside, heat demand is high and limit
control will raise boilers target temperature to provide heat.
When outside temperature is mild, heat demand is low.
Limit control will lower boiler’s target temperature saving
fuel.