2-5
SYSTEMS AND OPERATION
SFT 199 TANKLESS WATER HEATER
2.5 ADDING DOMESTIC HOT WATER
STORAGE
2.5.1 Tankless Domestic Hot Water with a Storage
Tank
The SFT series unit has the ability to connect a domestic hot water storage tank
to the unit to provide larger volumes of domestic hot water during peak demands.
The storage tank is piped to the unit’s domestic hot and cold water piping
connections. You must install a bronze or stainless steel pump to circulate water
from the storage tank through the unit’s domestic hot water coil.
In this case, (see g. 21) you will wire the pump and aquastat together without
connecting to the unit. When the line-voltage aquastat energizes the pump, the
the ow sensor detects the ow of domestic water and activates the water heater
to heat to its programmed temperature.
2.6 SEQUENCE OF OPERATION
When the unit is powered up the controller enters a self-diagnostic mode, and
displays “2” in the Service Display.
The sequence of operation is as follows:
1. The unit receives a call from domestic hot water heating from the internal
ow sensor.
2. The unit does a safety check and energizes the fan for a pre-purge (Service
Display = 3).
3. Once the 5-second pre-purge is compete, the unit enters a 5-second trial for
ignition (Service Display = 4). If the unit fails to ignite, the unit will complete a
5-second inter-purge then another 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 to allow for another attempt.
4. Once the burner is lit and ame has been proven the unit operates as it is
programmed (Service Display = + for domestic hot water).
5. If the unit reaches 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).
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