▶ Connect a line (A) from the outlet of the circulating pump
(installer supplied) to the inlet drain connection on the
water heater (see fig. 53.)
▶ Using another line (B), connect the outlet drain connection
on the water heater. Route the other end of this line into a
▶ Using a 3rd line (C) from the descaling reservoir, connect to
the inlet side of circulating pump. Install a filter on the end
of the line in the descaling reservoir.
▶ Make sure all connections are water tight.
▶ Fill the descaling reservoir with descaling solution so both
lines inside are submersed. We recommend a straight
white vinegar solution. If using a commercial descalant,
refer to manufacturer's instructions for proper dilution
▶ Ensure both drain connections are open.
▶ Operate the circulating pump.
▶ Make sure there are no leaks and the solution is flowing
from the descaling reservoir through the heater and
returning to the reservoir.
▶ Run the solution through the heater until the solution
returning to the descaling reservoir comes out clear.
(Changing to a fresh solution may be necessary during this
▶ Disconnect all lines and drain all solution from heat
exchanger. Properly discard the solution.
▶ Close the inlet drain connection.
▶ Position a container below the outlet drain connection and
connect the cold water supply. Open the cold water supply
shutoff valve and flush the heat exchanger with clean water.
▶ Close the cold water shutoff valve and reconnect hot water
supply to the water heater.
▶ Close the outlet drain connection.
▶ Reconnect the electrical supply to the unit, open the water
shutoff valves, and return the unit to service.
 Water filter
▶ If you are unable to perform the tasks listed below, or need
additional assistance please contact a service provider or
In some areas local code may require that the tasks described
in this section must be performed by a certified contractor.
▶ Please check your local codes to ensure compliance.
Many of the questions customers ask regarding operation of
this unit can be answered by following the troubleshooting
steps as outlined below. For best results, perform each step
before proceeding to the next. The suggested solutions may
require that the cover be taken off (see fig. 3, page 12).
Greentherm T9900 SE/i – 6 720 813 635 (2019/03)