LAARS NeoTherm NTV (Sizes 150–285 MBTU/h) - Service Manual - Manual (Page 106)

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Service Manual NeoTherm 80 - NeoTherm 285
Appendix 2 - Ignition and Firing Sequence App2
This is the basic operating sequence of the appliance whether there is a
DHW, or hydronic call for heat.
1. The unit receives a call for heat.
2. The controller does a check of the safety interlock chain.
3. The blower starts and the controller waits until it achieves prepurge
RPM.
4. The prepurge timer is started once the prepurge RPM is achieved.
5. The controller waits through a pre-ignition time of two seconds to
check the flame sensor operation and status. During this period an
intermittent spark can be seen.
6. The controller waits through a trial for ignition period of four seconds.
The direct spark ignition switches to constant spark for three sec-
onds, during which time the gas valve is open. For the last second of
the ignition period, direct spark is de-energized and the flame sensor
checks for established flame. If a flame is sensed, the control enters
“Run” to satisfy the demand. If flame is not established, the control
enters a retry, starting from step 2. If the flame has not been estab-
lished in the appropriate number of retries, the control will lockout
with a 109 error code.
7. The call for heat input disappears.
8. The gas valve shuts off.
9. The blower and pump continue to run through the overrun times to
purge the system.