Bosch Greentherm T9900 SE 160, Installation And Operating Instructions Manual

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Problem solving
67 Greentherm T9900 SE/i – 6 720 813 635 (2019/03)
9 Problem solving
9.1 Error code diagnostics
To remove error codes from the display,
▶ Touch the On/Off button more than 3 sec. (long press).
Installation, maintenance and repair must only be carried out
by qualified contractors. The following table describes the
solutions for possible problems.
Display Description Solution
A0 Water temperature sensors [17] [19] [20]
disconnected or damaged. ▶ Check sensor wire connections.
1) 2)
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A1 Air temperature inside the cabinet [18] is above
158 °F (70 °C). Appliance regulates power to
protect against overheat. ▶ External air temperature is above 140 °F (60 °C).
▶ Check for flue leakages inside the appliance or in
concentric vent.
1)
A2 External water temperature sensor/aquastat [21]
disconnected, damaged or not properly installed. ▶ Check temperature sensor and associated
connections.
1) 2)
▶ Check sensor position in the tank pocket.
▶ Verify if correct recirculation settings are in use
(

section 6.5.2).
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A3 Flue gases temperature sensor [15] disconnected
or damaged. ▶ Check sensor wire connections.
1) 2)
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A4 Air temperature sensor [18] disconnected or
damaged. ▶ Check sensor wire connections.
1) 2)
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A5 Condensing unit flue temperature sensor [16]
disconnected or damaged. ▶ Check sensor wire connections.
1) 2)
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A6 Inlet cold water temperature sensor [20]
disconnected or damaged. ▶ Check sensor wire connections.
1) 2)
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A7 Heat exchanger hot water temperature sensor [16]
disconnected or damaged. ▶ Check sensor wire connections.
1) 2)
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A8 Outlet hot water temperature sensor [17]
disconnected or damaged. ▶ Check connections or replace sensor.
1) 2)
▶ Replace the sensor and/or wire connections, if the
problem persists.
1)
A9 Incorrect output power (too low). ▶ Check gas inlet pressure
1)
(

section 4.13).
▶ Check water temperature sensors [17][19][20]
and water flow sensor [14] wire connections.
▶ Check sensors resistance and water flow sensor(

section 11) and replace any if it is not according to
specification.
1) 2)