Service bulletin
Descaling
TWH-G2-13
| 2400E, 2400EO, 250SX, 250SXO, 635ES, 635ESO
Introduction
Periodic descaling may be necessary in areas with high mineral
content in the water. Scale buildup in the heat exchanger may
result in lower
fl
ow rates, error codes of A7 and E9 and boiling
sounds in the heat exchanger.
Tools needed:
Various plumbing wrenches
Bucket for descaling solution
Small circulator or pump
Descaling using a pump
1. Disconnect electrical supply from the water heater.
2. Shut off the water supply to the water heater using (installer
supplied) isolation or shutoff valves.
3. Open hot water taps to drain and relieve pressure from the
plumbing system.
4. Drain water from the unit’s heat exchanger by disconnecting
inlet and outlet water connections from the heater.
5. Connect a line (A) from the outlet of the circulating pump
(installer supplied) to the inlet water
fi
tting on the water heater.
6. Connect another line (B) to the water outlet
fi
tting on the water
heater. Route the other end of this line into a descaling reservoir.
7. Using a 3rd line (C) from the descaling reservoir, connect to the
inlet side of circulating pump. Verify that there is a
fi
lter on the
end of the line in the descaling reservoir.
8. Make sure all connections are “hand tight.”
9. Fill tank with descaling solution so both lines inside are submer-
sed. We recommend straight white vinegar. If using a commer-
cial descalant, refer to manufacturer’s instructions on dilution
with water.
11. Operate the circulating pump.
12. Make sure there are no leaks and the solution is
fl
owing from the
descaling reservoir through the heater and returning to the
reservoir.
13. Run 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 process)
14. Disconnect all lines and drain all solution from heat exchanger.
Properly discard of solution.
15. Position a container below the hot water outlet and reconnect
cold water supply. Open cold water supply isolation valve and
fl
ush heat exchanger with clean water.
16. Shut cold water isolation valve and reconnect hot water line to
the water heater.
17. Reconnect electrical supply to unit, open water isolation valves,
and return the unit to service.
A
B
C
Pump
Filter
Descaling diagram
A
B
C
Pump
Filter
