Nibe F730 User guide

IHB EN 1916-1
531384
INSTALLER MANUAL
Exhaust air heat pump
NIBE F730 1x230 V

Quick guide
Navigation
Ok button (confirm/select)
Back button (back/undo/exit)
Control knob (move/increase/reduce)
A detailed explanation of the button functions can be found on page 41.
How to scroll through menus and make different settings is described on page 43.
Set the indoor climate
2X
INDOOR CLIMATE
HEAT PUMP INFO
HOT WATER
The mode for setting the indoor temperature is accessed by pressing the OK button twice, when in the start
mode in the main menu.
Increase hot water volume
2X
1X
To temporarily increase the amount of hot water, first turn the control knob to mark menu 2 (water droplet)
and then press the OK button twice.

41 Important information
4Safety information
4Symbols
4Marking
5Serial number
5Recovery
5Environmental information
5Country specific information
7Inspection of the installation
82 Delivery and handling
8Transport
8Assembly
9Supplied components
10Removing the covers
10Removing parts of the insulation
123 The heat pump design
12General
14Air treatment unit
154 Pipe and ventilation connections
15General pipe connections
17Dimensions and pipe connections
18Symbol key
18Cold and hot water
18Heating medium side
19Installation alternative
24General ventilation connection
24Ventilation flow
24Adjusting ventilation
25Dimension and ventilation connections
265 Electrical connections
26General
28Connections
31Settings
32Optional connections
35Connecting accessories
366 Commissioning and adjusting
36Preparations
36Filling and venting
37Start-up and inspection
40Basic values for the curve setting
417 Control - Introduction
41Display unit
42Menu system
458 Control - Menus
45Menu 1 - INDOOR CLIMATE
45Menu 2 - HOT WATER
46Menu 3 - INFO
46Menu 4 - HEAT PUMP
47Menu 5 - SERVICE
539 Service
53Maintenance
54Service actions
5810 Disturbances in comfort
58Info-menu
58Manage alarm
58Troubleshooting
6111 Accessories
6212 Technical data
62Dimensions and setting-out coordinates
64Technical specifications
66Energy labelling
68Electrical circuit diagram
74Item register
3Table of ContentsNIBE F730
Table of Contents

Safety information
This manual describes installation and service proced-
ures for implementation by specialists.
The manual must be left with the customer.
This appliance can be used by children
aged from 8 years and above and persons
with reduced physical, sensory or mental
capabilities or lack of experience and
knowledge if they have been given super-
vision or instruction concerning use of the
appliance in a safe way and understand
the hazards involved. Children shall not
play with the appliance. Cleaning and user
maintenance shall not be made by children
without supervision.
Rights to make any design or technical
modifications are reserved.
©NIBE 2018.
Water may drip from the safety valve's
overflow pipe, so this pipe must be inclined
along its entire length to prevent water
pockets. It must also be frost-proof. The
overflow pipe must be visible and its outlet
must be open.
F730 must be installed with a disconnection
option on the supply cable. Minimum cable
area must be sized according to the fuse
rating used. Electrical installation and wiring
must be carried out in accordance with applic-
able regulations.
Symbols
NOTE
This symbol indicates danger to person or ma-
chine .
Caution
This symbol indicates important information
about what you should consider when installing
or servicing the installation.
TIP
This symbol indicates tips on how to facilitate
using the product.
Marking
The CE mark is obligatory for most products sold in
the EU, regardless of where they are made.
CE
Classification of enclosure of electro-technical equip-
ment.
IP21
Read the User Manual.
Read the Installer Manual.
NIBE F730Chapter 1 | Important information4
1 Important information

Serial number
The serial number can be found at the bottom right of
the front cover and in the info menu (menu 3.1).
Serial number
Caution
You need the product's (14 digit) serial number
for servicing and support.
Recovery
Leave the disposal of the packaging to the in-
staller who installed the product or to special
waste stations.
Do not dispose of used products with normal
household waste. It must be disposed of at a
special waste station or dealer who provides this type
of service.
Improper disposal of the product by the user results in
administrative penalties in accordance with current le-
gislation.
Environmental
information
This unit contains a fluorinated greenhouse gas that is
covered by the Kyoto agreement.
F-GAS REGULATION (EU) NO. 517/2014
The equipment contains R407C, a fluorinated green-
house gas with a GWP value (Global Warming Potential)
of 1774. Do not release R407C into the atmosphere.
Country specific
information
UNITED KINGDOM
This installation is subject to building regulation approval,
notify the local Authority of intention to install.
Use only manufacturer’s recommended replacement
parts.
Benchmark places responsibilities on both manufactur-
ers and installers. The purpose is to ensure that custom-
ers are provided with the correct equipment for their
needs, that it is installed, commissioned and serviced
in accordance with the manufacturers instructions by
competent persons and that it meets the requirements
of the appropriate Building Regulations. The Benchmark
Checklist can be used to demonstrate compliance with
Building Regulations and should be provided to the
customer for future reference.
Installers are required to carry out the installation, com-
missioning and servicing work in accordance with the
Benchmark Code of practice which is available from the
Heating and Hotwater Industry Council who manage
and promote the Scheme. Visit www.centralheat-
ing.co.uk for information.
Warranty and insurance information
Thank you for installing a new NIBE heat pump in your
home.
NIBE heat pumps are manufactured in Sweden to the
very highest standard so we are pleased to offer our
customers a comprehensive guarantee.
The product is guaranteed for 24 months for parts and
labour from the date of installation or 33 months from
the date of manufacture, whichever is the shorter.
The NIBE guarantee is based on the unit being installed
and commissioned by a NIBE accredited installer, ser-
viced every year and the Benchmark documents com-
pleted. Where this condition is not met, any chargeable
spare parts or components issued within the applicable
guarantee period still benefit from a 12 month warranty
from the date of issue by the manufacturer.
We recommend the installer completes and returns as
soon as possible, your guarantee registration card or
completes the guarantee form on the NIBE website
www.nibe.co.uk.
Electrical Supply
The heat pump must be permanently connected to a
230V ac 50Hz supply.
All system components shall be of an approved type
and all wiring to current I.E.E wiring regulations.
External wiring must be correctly earthed, polarised and
in accordance with the relevant standards: Currently this
is BS 7671.
Domestic Hot Water
All domestic hot water circuits, connections and fittings
must be in accordance with the relevant standards and
water supply regulations. It should also be in accordance
5Chapter 1 | Important informationNIBE F730

with the relevant requirements of the Local Authority
and the Building Regulations relevant to the location of
installation.
BS 8558:2015 Services supplying water for domestic
use within buildings and their cartilages.
Water Supply (Water Fitting) Regulations 1999 or The
Water Bylaws 2000 (Scotland).
Heating System
The installation of the heat pump should follow best
practice as covered in the following:
BS 5449 Forced circulation hot water central heating
systems for domestic premises.
BS 15450 Heating systems in buildings – Design of heat
pump heating systems.
Ventilation System
Any ventilation system should be designed and installed
in accordance with Building Regulations, England &
Wales Approved Document F1 and Scotland Technical
Standard Section 3.14 Ventilation. Only this will ensure
hygienic room air and prevent any dampness to the
building structure.
To be able to ensure a high degree of efficiency and an
extremely comfortable living environment, we recom-
mend that the installation of any ventilation system
should be planned and this plan be strictly followed by
the ventilation engineer.
The discharge air duct work to outside must be insulated
to ensure condensation does not form in the duct work.
NIBE F730Chapter 1 | Important information6

Inspection of the installation
Current regulations require the heating installation to be inspected before it is commissioned. The inspection must
be carried out by a suitably qualified person. In addition, fill in the page for the installation data in the User Manual.
DateSignatureNotesDescription
✔
Ventilation (page 24)
Outdoor air damper
Setting ventilation flow exhaust air
Setting the ventilation flow outdoor air
Heating medium (page 18)
System flushed
System vented
Safety valve
Pressure in the climate system
Cold water (page 18)
Expansion vessel
Hot water (page 18)
Safety valve
Expansion vessel
T&P valve
Tundish
Electricity (page 26)
Connections
Main voltage
Phase voltage
Fuses heat pump
Fuses property
Outside sensor
Room sensor
Safety breaker
Earth circuit-breaker
Miscellaneous
Benchmark checklist
7Chapter 1 | Important informationNIBE F730

Transport
F730 is supplied in two sections and can be installed
separately or as one unit. The images in this manual
show F730 installed as one unit. For more information
see page 19.
F730 should be transported and stored vertically in a dry
place. However. the F730 may be carefully laid on its
back when being moved into a building. The centre of
gravity is in the upper part.
R
0
R
0
Assembly
• Position F730 on a fixed foundation that can take the
weight of the heat pump. Use the product's adjustable
feet to obtain a horizontal and stable set-up.
Because water comes from F730, the floor coating is
important. A waterproof floor or floor membrane is
recommended.
30 - 50 mm
30 - 50 mm
15 - 40 mm
20-55 mm
•Install with its back to an outside wall, ideally in a room
where noise does not matter, in order to eliminate
noise problems. If this is not possible, avoid placing
it against a wall behind a bedroom or other room
where noise may be a problem.
• Wherever the unit is located, walls to sound sensitive
rooms should be fitted with sound insulation.
• Route pipes so they are not fixed to an internal wall
that backs on to a bedroom or living room.
• The heat pump's installation area should always have
a temperature of at least 10 °C and max 30 °C.
NIBE F730Chapter 2 | Delivery and handling8
2 Delivery and handling

INSTALLATION AREA
Leave a free space of 800 mm in front of the product.
Leave free space between F730 and wall/other ma-
chinery/fittings/cables/pipes etc. It is recommended that
a space of at least 10 mm is left to reduce the risk of
noise and of any vibrations being propagated.
800
100
NOTE
Ensure that there is sufficient space (300 mm)
above the heat pump for installing ventilation
hoses.
Supplied components
Room sensorOutside sensor
LEK
Extra air filterVent hose
(length 4 m)
LEK
LEK
Gasket2 x tundish
LEK
LEK
Outdoor air damperExpansion vessel with
holder
(supplied separately)
Ambient sensor
Damper motor incl. 2
screws
Clips Screw
O-rings
Front hatch,
air treatment section
LEK
Side panels,
air treatment unit
LOCATION
The kit of supplied items is placed on top of the product.
9Chapter 2 | Delivery and handlingNIBE F730

Removing the covers
FRONT COVER
LEK
LEK
4
1
2
3
1. Remove the upper panel by pulling it straight out.
2. Remove the screws from the lower edge of the
front panel.
3. Lift the panel out at the bottom edge and up.
4. Pull the panel towards yourself.
SIDE COVERS
LEK
LEK
LEK
The side covers can be removed to facilitate the install-
ation.
1. Remove the screws from the upper and lower
edges.
2. Twist the cover slightly outward.
3. Move the hatch backwards and slightly to the side.
4. Pull the cover to one side.
5. Pull the hatch forwards.
Removing parts of the
insulation
Parts of the insulation can be removed to facilitate the
installation.
INSULATION, TOP
1. Disconnect the cable from the motor and remove
the motor from the shuttle valve as illustrated.
LEK
LEK
LEK
LEK
A
B
2. Grip the handle and pull straight out as illustrated.
LEK
LEK
NIBE F730Chapter 2 | Delivery and handling10

INSULATION, IMMERSION HEATER
NOTE
Electrical installation and service must be car-
ried out under the supervision of a qualified
electrician. Electrical installation and wiring
must be carried out in accordance with the
stipulations in force.
1. Remove the cover for the junction box according to
the description on page 27.
2. Grip the handle and pull the insulation carefully to-
wards you as illustrated.
LEK
1
2
LEK
TIP
Remove the hatch for the immersion heater
card so that it is easier to remove the insulation
(see page 27).
11Chapter 2 | Delivery and handlingNIBE F730

General
LEK
LEK
LEK
QN10
AA1
FC1
BT7
BT2
PZ1
PZ3
EB1
BT30
FQ10
XL4 XL3 XL1
RF3
AA2
BT6
AA23
AA3
AA4-XF3
AA4-XF4
SF1
AA4
UB2
UB1
W130
GP1
XL2
QM22QM26 QM20
BP5
WP3
FL1QZ2 FL2
QM13QM11
WP1
WP2
WM2
WM1
RM1
CM1 XL10
WM6
XL5
QM17
XL29
FL5
XL15
NIBE F730Chapter 3 | The heat pump design12
3 The heat pump design

PIPE CONNECTIONS
Connection, heating medium flow lineXL1
Connection, heating medium return lineXL2
Connection, cold waterXL3
Connection, hot waterXL4
Connection, hot water circulationXL5
Connection, draining heating mediumXL10
Connection, balanced cold waterXL15
Connection, T&P valveXL29
HVAC COMPONENTS
Expansion vesselCM1
Expansion relief valve, safety valve, hot water
heater
FL1
Safety valve, climate systemFL2
T&P valveFL5
Circulation pumpGP1
Filler valve, climate systemQM11
Filler valve 2, climate systemQM13
Venting, heating mediumQM20
Venting, coilQM22
Venting, heating medium 2QM26
Shuttle valve, climate system/water heaterQN10
Pressure reduction valve with integrated check valveQN17
FilterballQZ2
Non-return valveRM1
Overflow cupWM1
Overflow water dischargeWM2
Water sealWM6
Overflow pipe, safety valve hot water heaterWP1
Overflow pipe, safety valve climate systemWP2
Overflow pipe, condensationWP3
SENSORS ETC.
Level monitor for the overflow cupBL3
Pressure gauge, heating systemBP5
Outside sensor1 BT1
Temperature sensors, heating medium flowBT2
Temperature sensor, hot water, controlBT6
Temperature sensor, hot water, displayBT7
Thermostat, backup heatingBT30
Room sensor1 BT50
ELECTRICAL COMPONENTS
Immersion heater cardAA1
Base cardAA2
Input circuit boardAA3
Display unitAA4
AA4-XF3 USB socket
AA4-XF4 Service socket
Communication boardAA23
Immersion heaterEB1
Miniature circuit-breakerFC1
Temperature limiterFQ10
EMC cardRF3
SwitchSF1
Network cable for NIBE UplinkTM W130
MISCELLANEOUS
Rating platePZ1
Serial number platePZ3
Cable glandUB1-2
1Not visible in the image
Designations in component locations according to standard IEC 81346-
2.
13Chapter 3 | The heat pump designNIBE F730

Air treatment unit
LEK
LEK
LEK
LEK
BP2
BT21
BT3
QM24
GQ2
GQ10
BT14
BP1
AA101
BT16
EP1
QN1
BT17
BS1
BT20
QQ1
CA1 QA40
RA1
XL31
XL32
EB16
FQ12
HZ2
BT15
BT12
EP2
PIPE CONNECTIONS
Ventilation connection, exhaust airXL31
Ventilation connection, extract airXL32
HVAC COMPONENTS
Venting, heat exchangerQM24
SENSORS ETC.
High pressure pressostatBP1
Low pressure pressostatBP2
Air speed sensorBS1
Temperature sensors, heating medium returnBT3
Temperature sensor, heating medium flow after
condenser
BT12
Temperature sensor, hot gasBT14
Temperature sensor, fluid pipeBT15
Temperature sensor, evaporator1 BT16
Temperature sensor, suction gasBT17
Temperature sensor, exhaust airBT20
Temperature sensor, extract airBT21
ELECTRICAL COMPONENTS
Connection card sensorAA101
CapacitorCA1
Defrosting elementEB16
Temperature limiter, defrosting elementFQ12
InverterQA40
ChokeRA1
COOLING COMPONENTS
EvaporatorEP1
CondenserEP2
CompressorGQ10
Drying filterHZ2
Expansion valveQN1
VENTILATION
Exhaust air fanGQ2
Exhaust air filter1 HQ10
Filter cover, exhaust airQQ1
1Not visible in the image
Designations in component locations according to standard IEC 81346-
2.
NIBE F730Chapter 3 | The heat pump design14

General pipe
connections
Pipe installation must be carried out in accordance with
current norms and directives.
The system requires the radiator circuit to be designed
for a low temperature heating medium. At the lowest
dimensioned outdoor temperature (DOT) the highest
recommended temperatures are 55 °C on the supply
line and 45 °C on the return line.
NOTE
The pipe system needs to be flushed out be-
fore the heat pump is connected so that any
debris cannot damage component parts.
NOTE
This installation is subject to building regulation
approval, notify the local Authority of intention
to install.
NOTE
Use only manufacturer’s recommended replace-
ment parts.
Overflow water from the safety valves and the evapor-
ator’s collection tray passes via a non-pressurised over-
flow pipe to a drain, so that hot water splashes cannot
cause injury. The mouth of the overflow pipe must be
visible and not placed close to electrical components.
In addition, the mouth of the overflow pipe (tundish),
drain valves and motorised valves should be positioned
away from all electrical components. This is the only
permitted use of non-pressurised overflow pipe. Over-
flow pipes from tundish connected to the expansion
relief valve must also be connected to the drain in the
same way.
Please note that the connection of the T&P-valve should
not be used for any other purpose.
Valves may not be positioned between the safety valve
and the water heater.
Overflow pipes from tundish must be routed with a fall
and be at least 300 mm long, before bends or angles in
the pipework (see image) and must also be frost-proof.
Matal discharge pipe
from tundish, with
continous fall.
Min. 300 mm
Tundish
Safety device
(e.g. temperature
relief valve)
Metal discharge pipe
from temperature relief
valve to tundish
Possible
wall
Discharge
below fixed
grating
Fixed
grating
Trapped
gulley
Max 600 mm
Resistance created by
each elbow or bend
Maximum resistance
allowed, expressed as
a lenght of straight pipe
(i.e. no elbows or
bends)
Minimum size of dis-
charge pipe from tun-
dish
Minimum size of dis-
charge pipe
Valve outlet size
0.8 mmup to 9 m22 mm15 mmG1/2
1.0 mmup to 18 m28 mm15 mmG1/2
1.4 mmup to 27 m35 mm15 mmG1/2
1.0 mmup to 9 m28 mm22 mm<G3>/4
1.4 mmup to 18 m35 mm22 mm<G3>/4
1.7 mmup to 27 m42 mm22 mm<G3>/4
1.4 mmup to 9 m35 mm28 mmG1
15Chapter 4 | Pipe and ventilation connectionsNIBE F730
4 Pipe and ventilation
connections

Resistance created by
each elbow or bend
Maximum resistance
allowed, expressed as
a lenght of straight pipe
(i.e. no elbows or
bends)
Minimum size of dis-
charge pipe from tun-
dish
Minimum size of dis-
charge pipe
Valve outlet size
1.7 mmup to 18 m42 mm28 mmG1
2.3 mmup to 27 m54 mm28 mmG1
HARD WATER AREAS
Usually, there should not be a problem in installing F730
in areas of hard water as the operating temperature is
50-60 °C.
CLEANING THE CLIMATE SYSTEM
When the water heater and the climate system have
been filled with water, F730 must operate at maximum
normal temperature for at least one hour. Thereafter the
system must be drained of water and refilled. See sec-
tion Draining the climate system on page 54.
Before installing the heat pump in an existing system,
it is important that the system is properly flushed
through.
Even if the heat pump is to be installed in a new system,
the heat pump and system should be flushed.
NOTE
Ensure that cleaning agent has been removed
from the entire system before adding inhibitor.
After flushing an inhibitor should be used for long-term
anti-corrosion protection.
NIBE Energy Systems Limited recommends water
treatments (supplied by e.g. Fernox and Sentinel) spe-
cifically designed for heat pumps.
Caution
Ensure that incoming water is clean. When
using a private well, it may be necessary to
supplement with an extra water filter.
MAX. VOLUME IN THE HEATING SECTION
AND THE CLIMATE SYSTEM
H
The volume of the pressure expan-
sion vessel (CM1) is 10 litres and it
is pre-pressurised as standard to 0.5
bar (5 mvp). As a result, the maxim-
um permitted height “H” between
the expansion vessel and the highest
installed radiator is 5 m, see figure.
If the pre-pressure is not high
enough, it can be increased by
adding air via the valve in the expan-
sion vessel. The expansion vessel’s
pre-pressure must be stated in the inspection document.
Any change in the pre-pressure affects the ability of the
expansion vessel to handle the expansion of the water.
The maximum system volume, excluding the heating
section, is 285 litres at the above pre-pressure.
NIBE F730Chapter 4 | Pipe and ventilation connections16

SYSTEM DIAGRAM
When the exhaust air at room temperature passes
through the evaporator, the refrigerant evaporates be-
cause of its low boiling point. In this way the energy in
the room air is transferred to the refrigerant.
The refrigerant is then compressed in a compressor,
causing the temperature to rise considerably.
The warm refrigerant is led to the condenser. Here the
refrigerant gives off its energy to the heating system
water, whereupon the refrigerant changes state from
gas to liquid.
The refrigerant then goes via filters to the expansion
valve, where the pressure and temperature are reduced.
The refrigerant has now completed its circulation and
returns to the evaporator.
FrånluftAvluft
XL2 XL1XL3XL4
Extract air Exhaust air and any outdoor air
Connection, heating medium flowXL1
Connection, heating medium returnXL2
Cold water connectionXL3
Hot water connectionXL4
Caution
This is a principle of operation, differences may
occur in the installation in question.
Dimensions and pipe
connections
B
C
A
F750
LEK
XL2 XL4 XL3 XL1 WM1XL15
The overflow cup (WM1) can be turned, so that the pipe
can be directed forwards or backwards to simplify con-
nection of the hose to the drain.
SETTING OUT DIMENSIONS
CBAConnection
105285150(mm)XL1 Heating medium supply
365285220(mm)XL2 Heating medium return
195445210(mm)XL3 Cold water
260405300(mm)XL4 Hot water
195405220(mm)XL15 Balanced cold water
50280195(mm)WM1 Overflow cup
PIPE DIMENSIONS
Connection
22(mm)XL1-XL2 Heating medium ext Ø
22(mm)XL3 Cold water ext Ø
22(mm)XL4 Hot water ext Ø
15(mm)XL5 Hot water circulation ext. Ø
22(mm)XL15 Balanced cold water
15(mm)XL29 Connection, T&P valve
32(mm)WM2 Overflow water discharge
17Chapter 4 | Pipe and ventilation connectionsNIBE F730

Symbol key
MeaningSymbol
Shut-off valve
Non-return valve
Mixing valve
Shunt / shuttle valve
Safety valve
Temperature sensor
Circulation pump
Radiator system
Domestic hot water
Under floor heating systems
Cold and hot water
CONNECTING COLD AND HOT WATER
• A mixer valve must also be installed, if the factory
setting for hot water is changed. National regulations
must be observed.
• The setting for hot water is made in menu 5.1.1 (page
48).
XL4 XL3
Heating medium side
CONNECTING THE CLIMATE SYSTEM
A climate system is a system that regulates indoor
comfort with the help of the control system in F730 and
for example radiators, under floor heating/cooling, fan
coils etc.
• When connecting to a system with thermostats on all
radiators, a relief valve must be fitted, or some of the
thermostats must be removed to ensure sufficient
flow.
XL2 XL1
NIBE F730Chapter 4 | Pipe and ventilation connections18

Installation alternative
F730 can be installed in several different ways, some
of which are shown below.
Further option information is available at www.nibe.co.uk
and in the respective assembly instruction for the ac-
cessory used. See page 61 for a list of accessories that
can be used with F730.
SEPARATED/ONE UNIT
F730 is delivered separated and can be installed separ-
ated or as one unit. For separate installation the access-
ory DKI 10 is required. Clips, o-rings and screws are
supplied for both types of installation.
The images in this manual show F730 installed as one
unit.
LEK
LEK
Separated installationOne unit
One unit
1. Remove the heater unit front hatch (see page 10).
2. Remove the insulation at the immersion heater (see
page 11).
3. Remove the motor for the reversing valve for the
climate system/water heater (QN10) (see page 10).
4. Remove the top insulation (see page 10).
5. Place the air treatment unit above the water heater
unit by sliding the rear part of the air treatment unit
into the water heater unit.
6. Then lower the front part of the air treatment unit.
The locking tabs are then located in grooves in the
heater unit.
7. Secure condensation hoses in the air treatment unit.
TIP
Lift the air treatment unit slightly at the
front edge so that it is easier to access.
8. Install an overflow cup and route the condensation
hose to it.
19Chapter 4 | Pipe and ventilation connectionsNIBE F730

9. Connect the air treatment unit flexible pipes to the
heater unit. Use the o-rings and clips supplied.
10. Connect the air treatment unit wiring to the heater
unit.
APH
11. Secure the air treatment unit lock tabs in the water
heater unit with 2 of the screws supplied.
12. Install the reversing valve motor and the heater unit
insulation.
13. Secure the side panels on the air treatment unit with
2 of the remaining screws supplied. The side panels
mounting points may need to be adjusted slightly.
LEK
Side hatches mounting points
14. Install the front panels on the air treatment and
heater units.
NIBE F730Chapter 4 | Pipe and ventilation connections20