A.O. Smith TWI 35-200, Installation, User And Service Manual

Page: 77 / 92

Code and
description Cause Measure
Not enough pressure differential across
the air proving switch, due to:
- venting system
- malfunction condensation
discharge
- dirty burner
- blocked heat exchanger
Check, after each fix, if the error reappears.
If the error reappears continue in finding
the cause.
- Measure the pressure differential
across the air proving switch, refer to
Air pressure differential.
Venting system (see 8.7):
- Make sure if the venting system is
compliant.
- Make sure that the venting system has
no blockages.
- Make sure if the air inlet screen has no
blockages.
Condensation discharge:
- Make sure the condensate drain has
no blockages.
- Make sure that the condensate drain is
connected to the waste water
discharge by an open connection.
Burner:
- Make sure that the the burner is clean
(see 11.4.1).
- Measure the pressure differential
across the air proving switch again. If
the pressure differential is insufficient,
clean the heat exchanger.
- Use a multimeter to make sure that
the air proving switch is closed.
XAC-XXXX
(blocking error)
Fan error
Switch is closed when fan
is not running.
Damaged wiring/closed circuit. - Make sure that the wiring, between
the air proving switch and the
controller, is connected and not
damaged.
- If necessary replace the wires or
reconnect the wires. Reset the
controller, when wires are replaced or
reconnected.
Air proving switch defect. - Make sure that the air proving switch
works properly.
- If necessary, replace the air proving
switch.
- When the air proving switch is
replaced and reconnected, reset the
controller.
0313279_TWISTER II_UKUK_
V1.1, 18-02-2019
77