2-5
SYSTEMS AND OPERATION
TANKLESS WATER HEATER 199
2.5 SEQUENCE OF OPERATION
When the unit is powered up the controller enters a self-diagnostic mode, and
displays the controller software version in the main display.
The sequence of operation is as follows:
1.
The unit receives a call for
for
domestic hot water heating from the internal flow
sensor.
2.
The unit performs a safety check and energizes the fan for a pre-purge
(
Service Display = 3
).
3.
Once the 5-second pre-purge is complete, the unit enters a 5-second trial for
ignition (
Service Display = 4
). If the unit fails to ignite, the unit will complete
another 5-second pre-purge then 5-second trial for ignition. This is repeated
4 times before a hard lock-out occurs. The Return button must be pressed
to reset the controller and begin another trial for ignition.
4.
Once the burner is lit and flame has been proven the unit operates as it is
programmed (
Display
= + for domestic hot water).
5.
If the unit exceeds its target temperature and there is still a call for hot water
the burner will turn off. (
Service Display = 1
)
6.
If the burner is on to maintain the heat exchanger temperature for DHW
Comfort mode (
Service Display = 7
).
7.
If the burner is on for frost protection (
Service Display = 9
).
MAIN
DISPLAY
SERVICE
DISPLAY
DESCRIPTION
OFF
-
The unit is OFF. Press the space above the dot for 2
seconds to turn on the unit
.
(blank)
(blank)
No Call for Hot Water - Standby
XXX
1
Unit water temperature exceeds target, call still present
XXX
2
Self-test – When power is applied to the unit the
controller enters a self diagnostic mode for 5 seconds
XXX
3
Fan Pre-purge and Post-purge
XXX
4
Trial for Ignition and Flame Proving
XXX
+
Heating – DHW
XXX
7
Burner on for DHW Comfort mode
XXX
9
Freeze Protection mode
Table 8: Operating Display and Service Display Codes.