VENTILATION SYSTEM
Check the following:
1. The air filter. Clean or replace if necessary.
2. Any dirt on the fan. Clean if necessary.
3. Ensure that the ventilation openings are not blocked.
4. The airflow. Adjust if necessary.
5. Ensure that the damper motor is not blocked.
Correct any fault before continuing.
SAFETY VALVES
S735 has three safety valves, two for the hot water and one
for the climate system.
The function of the safety valves must be checked regularly.
The valves are accessed via the service hatch. Perform
checks as follows:
1. Open the valve by turning the knob anti-clockwise
carefully.
2. Check that water flows through the valve.
3. Close the valve by releasing it. If it does not close auto-
matically when released, turn it anti-clockwise slightly.
4. The climate system may need to be refilled after
checking the safety valve, see section "Filling the climate
system".
Service actions
EMERGENCY MODE
NOTE
Do not start the system before filling up with wa-
ter. Components in the system could be damaged.
Emergency mode is used in event of operational interference
and in conjunction with service.
You can activate the emergency mode both when S735 is
running and when it is switched off.
When the emergency mode is active, the status lamp is yel-
low.
To activate when S735 is running: press and hold the on/off
button (SF1) for 2 seconds and select "emergency mode"
from the shutdown menu.
To activate emergency mode when S735 is switched off:
press and hold the on/off button (SF1) for 5 seconds. (De-
activate the emergency mode by pressing once.)
When S735 is put in emergency mode, the display is switched
off and the most basic functions are active:
• The immersion heater works to maintain the calculated
supply temperature. If there is no outdoor temperature
sensor (BT1), the immersion heater works to maintain the
maximum supply temperature, set in menu 1.30.6 -
"Highest supply heat".
• The compressor is off and only the fan, the heating medi-
um pump and the electric additional heat are active. The
immersion heater is stepped according to the setting in
menu 7.1.8.2 - "Emergency mode".
DRAINING THE HOT WATER HEATER
The water heater can be drained through the safety valve
(FL1) or via the overflow cup (WM1).
NOTE
There may be some hot water, risk of scalding.
1. Disconnect the overflow pipe from the safety valve (FL1)
and connect a hose to a draining pump instead. If a
draining pump is not available, the water can be released
directly into the overflow cup instead (WM1).
2. Open the safety valve (FL1).
3. Open a hot water tap to let air into the system. If this is
not sufficient, detach the pipe connection (XL4) on the
hot water side and ensure that air is entering.
DRAINING THE CLIMATE SYSTEM
In order to carry out service on the climate system, it may
be easier to drain the system first.
NOTE
There may be some hot water, risk of scalding.
The hot water can drained as follows:
• through the draining valve (XL10)
• through the safety valve (FL2) via the overflow cup (WM1)
• through a hose that is connected to the safety valve’s
(FL2) outlet
1. Open the safety valve/drain valve.
2. Set the vent valves for the climate system (QM20),
(QM22), (QM24), (QM26) in the open position for air
supply.
NOTE
The heat pump should not, after draining, be ex-
posed to risk of freezing because a certain of water
remains in the coil.
59Chapter 10 | ServiceNIBE S735
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