A.O. Smith SGS - 100 Supplement

80
100
Installation
User and
Service Manual
Installation
User and
Service Manual

www.aosmithinternational.com
your installer

Instruction manual SGS 3
gis
Read this manual carefully Warning
Read this manual carefully before starting up the water heater. Failure to
read this manual and to follow the instructions in this manual may lead to
accidents, personal injury, and damage to the appliance.
Copyright © 2008 A.O. Smith water Products Company
All rights reserved.
Nothing from this publication may be copied, reproduced and/or published by
means of printing, photocopying or by whatsoever means, without the prior
written approval of A.O. Smith water Products Company.
A.O. Smith water Products Company reserves the right to modify specifications
stated in this manual.
Trademarks Any brand names mentioned in this manual are registered trademarks of their
respective owners.
Liability A.O. Smith water Products Company accepts no liability for claims from third
parties arising from improper use other than that stated in this manual and in
accordance with the General Conditions registered at the Eindhoven Chamber
of Commerce.
Refer further to the General Conditions. These are available on request, free of
charge.
Although considerable care has been taken to ensure a correct and suitably
comprehensive description of all relevant components, the manual may
nonetheless contain errors and inaccuracies.
Should you detect any errors or inaccuracies in the manual, we would be
grateful if you would inform us. This helps us to further improve our
documentation.
More information If you have any comments or queries concerning any aspect related to the
appliance, then please do not hesitate to contact:
A.O. Smith water Products Company
PO Box 70
5500 AB Veldhoven
Netherlands
Telephone: (free) 008008 - AOSMITH
0870 - 267 64 84
General: [phone]
Fax: [phone]
E-mail : [e-mail]
Website: www.aosmithinternational.com
In the event of problems with connecting to the gas, electricity or water supply,
please contact your installation's supplier/installation engineer .

4Instruction manual SGS
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Instruction manual SGS 5
Table of contents
1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - 9
1.1 About the appliance - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9
1.2 What to do if you smell gas- - - - - - - - - - - - - - - - - - - - - - - - - 9
1.3 Regulations - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9
1.4 Target groups - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10
1.5 Maintenance - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10
1.6 Forms of notation - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10
1.7 Overview of this document - - - - - - - - - - - - - - - - - - - - - - - - 11
2 Working principle of the appliance- - - - - - - - - - - - - - - 13
2.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 13
2.2 General working principle of the appliance - - - - - - - - - - - - - - - - 13
2.3 The appliance's heating cycle - - - - - - - - - - - - - - - - - - - - - - 14
2.4 Protection for the appliance - - - - - - - - - - - - - - - - - - - - - - - 15
2.5 Safety of the installation - - - - - - - - - - - - - - - - - - - - - - - - - 17
3 Installation - - - - - - - - - - - - - - - - - - - - - - - - - - - 19
3.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19
3.2 Packaging - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19
3.3 Environmental conditions- - - - - - - - - - - - - - - - - - - - - - - - - 19
3.4 Technical specifications - - - - - - - - - - - - - - - - - - - - - - - - - 22
3.5 Installation diagram - - - - - - - - - - - - - - - - - - - - - - - - - - - 25
3.6 Water connections, Vented - - - - - - - - - - - - - - - - - - - - - - - - 26
3.7 Water connections, Unvented - - - - - - - - - - - - - - - - - - - - - - 27
3.8 Gas connection - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 28
3.9 Solar heating system- - - - - - - - - - - - - - - - - - - - - - - - - - - 28
3.10 Air supply and flue - - - - - - - - - - - - - - - - - - - - - - - - - - - - 28
3.11 Electrical connection - - - - - - - - - - - - - - - - - - - - - - - - - - - 35
3.12 Electrically connecting the solar heating system controller- - - - - - - - - 38
3.13 Checking the supply pressure and burner pressure - - - - - - - - - - - - 41
4 Conversion to a different gas category - - - - - - - - - - - - 45
5 Filling - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 47
5.1 Installation diagram - - - - - - - - - - - - - - - - - - - - - - - - - - - 47
5.2 Filling unvented installations - - - - - - - - - - - - - - - - - - - - - - - 48
5.3 Filling vented installations - - - - - - - - - - - - - - - - - - - - - - - - 48
5.4 Filling solar heating system- - - - - - - - - - - - - - - - - - - - - - - - 49
6 Draining - - - - - - - - - - - - - - - - - - - - - - - - - - - - 51
6.1 Installation diagram - - - - - - - - - - - - - - - - - - - - - - - - - - - 51
6.2 Draining unvented installations - - - - - - - - - - - - - - - - - - - - - - 52
6.3 Draining vented installations - - - - - - - - - - - - - - - - - - - - - - - 53
6.4 Draining solar heating system - - - - - - - - - - - - - - - - - - - - - - 54
7 The control panel- - - - - - - - - - - - - - - - - - - - - - - - 55
7.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 55
7.2 Controls - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 55
7.3 Meaning of icons- - - - - - - - - - - - - - - - - - - - - - - - - - - - - 55
7.4 Electronic controller ON/OFF switch - - - - - - - - - - - - - - - - - - - 55
7.5 Navigation buttons - - - - - - - - - - - - - - - - - - - - - - - - - - - - 56
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Table of contents
6Instruction manual SGS
7.6 PC connection - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 56
8 Status of the appliance - - - - - - - - - - - - - - - - - - - - - 57
8.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 57
8.2 Operating modes - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 57
8.3
EXTRA - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 57
8.4 Error conditions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 58
8.5 Service condition - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 58
9 Starting and running - - - - - - - - - - - - - - - - - - - - - - 59
9.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 59
9.2 Starting the appliance - - - - - - - - - - - - - - - - - - - - - - - - - - - 59
9.3 The appliance's heating cycle - - - - - - - - - - - - - - - - - - - - - - - 59
10 Shutting down - - - - - - - - - - - - - - - - - - - - - - - - - 61
10.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 61
10.2 Shut the appliance down for a brief period ("OFF mode")- - - - - - - - - - 61
10.3 Electrically isolating the appliance - - - - - - - - - - - - - - - - - - - - - 61
10.4 Shutting the appliance down for a long period - - - - - - - - - - - - - - - 61
11 Main menu - - - - - - - - - - - - - - - - - - - - - - - - - - - 63
11.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 63
11.2 Notational convention for menu-related instructions - - - - - - - - - - - - 63
11.3 Switching on the "ON mode" - - - - - - - - - - - - - - - - - - - - - - - 63
11.4 Setting the water temperature - - - - - - - - - - - - - - - - - - - - - - - 63
11.5 Week program - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 64
11.6 Starting and stopping the week program - - - - - - - - - - - - - - - - - - 64
11.7 Changing the appliance's standard week program - - - - - - - - - - - - - 64
11.8 Adding times to a week program- - - - - - - - - - - - - - - - - - - - - - 66
11.9 Deleting times from a week program- - - - - - - - - - - - - - - - - - - - 67
11.10 Extra period- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 67
11.11 Programming an extra period - - - - - - - - - - - - - - - - - - - - - - - 68
11.12 Settings- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 69
12 Service program - - - - - - - - - - - - - - - - - - - - - - - - 71
12.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 71
12.2 Setting the hysteresis - - - - - - - - - - - - - - - - - - - - - - - - - - - 71
12.3 Displaying the error history - - - - - - - - - - - - - - - - - - - - - - - - 71
12.4 Displaying the appliance history - - - - - - - - - - - - - - - - - - - - - - 71
12.5 Display the selected appliance - - - - - - - - - - - - - - - - - - - - - - 72
12.6 Setting the service interval - - - - - - - - - - - - - - - - - - - - - - - - 72
12.7 Setting legionella prevention- - - - - - - - - - - - - - - - - - - - - - - - 72
12.8 Solar heating system configuration - - - - - - - - - - - - - - - - - - - - 72
12.9 Setting the central heating configuration - - - - - - - - - - - - - - - - - - 74
13 Troubleshooting - - - - - - - - - - - - - - - - - - - - - - - - 75
13.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 75
13.2 Troubleshooting table for general errors - - - - - - - - - - - - - - - - - - 76
13.3 Troubleshooting table for displayed errors - - - - - - - - - - - - - - - - - 79
13.4 Displayed warnings - - - - - - - - - - - - - - - - - - - - - - - - - - - - 90
14 Maintenance frequency - - - - - - - - - - - - - - - - - - - - - 91
14.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 91
14.2 Determining service interval - - - - - - - - - - - - - - - - - - - - - - - - 91

Instruction manual SGS 7
15 Performing maintenance - - - - - - - - - - - - - - - - - - - - 93
15.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 93
15.2 Preparation for maintenance - - - - - - - - - - - - - - - - - - - - - - - 93
15.3 Water-side maintenance - - - - - - - - - - - - - - - - - - - - - - - - - 95
15.4 Gas-side maintenance - - - - - - - - - - - - - - - - - - - - - - - - - - 96
15.5 Solar collector maintenance - - - - - - - - - - - - - - - - - - - - - - - 96
15.6 Finalizing maintenance- - - - - - - - - - - - - - - - - - - - - - - - - - 96
16 Warranty (certificate) - - - - - - - - - - - - - - - - - - - - - - 97
16.1 General warranty - - - - - - - - - - - - - - - - - - - - - - - - - - - - 97
16.2 Tank warranty - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 97
16.3 Conditions for Installation and use - - - - - - - - - - - - - - - - - - - - 97
16.4 Exclusions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 98
16.5 Scope of the warranty - - - - - - - - - - - - - - - - - - - - - - - - - - 98
16.6 Claims - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 98
16.7 Obligations of A.O. Smith - - - - - - - - - - - - - - - - - - - - - - - - 98
17 Appendices- - - - - - - - - - - - - - - - - - - - - - - - - - - 99
17.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 99
17.2 Menu structure - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 100
17.3 Electrical diagram for the appliance- - - - - - - - - - - - - - - - - - - - 102
17.4 Electrical diagram, solar heating system - - - - - - - - - - - - - - - - - 104
17.5 Week program card - - - - - - - - - - - - - - - - - - - - - - - - - - - 107

Table of contents
8Instruction manual SGS

Instruction manual SGS 9
gis
1 Introduction
1.1 About the appliance This manual describes how to install, service and use the SGS appliance. The
SGS appliance is a condensing boiler with a fan in the air intake. The appliance
is always supplied including a storage tank fitted with a heat exchanger
connected to a solar energy source.
The SGS can be installed as either an open or room-sealed appliance. A
concentric chimney connector is fitted standard to the appliance, but a parallel
system can also be connected.
The alternative installation types are B23, C13, C33, C43, C53 and C63.
The information in this manual applies to the: SGS 80 and SGS 100.
The appliance has been manufactured and equipped in accordance with the
European standard for gas-fired storage water heaters for the production of
domestic hot water (EN 89). The appliances are therefore compliant with the
European Directive for Gas Appliances, and are entitled to bear the CE mark.
Warning
Read this manual carefully before starting up the installation. Failure to read
the manual and to follow the printed instructions may lead to personal injury and
damage to the appliance.
1.2 What to do if you
smell gas
Warning
If there is a gas smell:
No naked flames! No smoking!
Avoid causing sparks! Do not use any electrical equipment or switch, i.e. no
telephones, plugs or bells!
Open windows and doors!
Shut off the mains gas supply valve!
Warn occupants and leave the building!
After leaving the building, alert the gas distribution company or your installation
engineer.
1.3 Regulations As the (end) user, installation engineer or service and maintenance engineer,
you must ensure that the entire installation complies, as a minimum, with the
official local:
• building regulations;
• energy supplier's directives for existing gas installations;
• directives and technical guidelines for natural gas installations;
• safety requirements for low-voltage installations;
• regulations governing the supply of drinking water;
• regulations governing ventilation in buildings;
• regulations governing the supply of air for combustion;
• regulations governing the discharge of products of combustion;
• requirements for installations that consume gas;
• regulations governing indoor waste water disposal;
• regulations imposed by fire brigade, power companies and municipality.
0063

Introduction
10 Instruction manual SGS
1gis
Furthermore, the installation must comply with the manufacturer's instructions.
Note
Later amendments and/or additions to all regulations, requirements and
guidelines published on or prior to the moment of installing, will apply to the
installation.
1.4 Target groups The three target groups for this manual are:
• (end) users;
• installation engineers;
• service and maintenance engineers.
Symbols on each page indicate the target groups for whom the information is
intended. See the table.
Target group symbols
1.5 Maintenance A service should be carried out at least once a year, both on the water side and
on the gas side. Maintenance frequency depends, among other things, on the
water quality, the average burning time per day and the set water temperature.
Note
To determine the correct maintenance frequency, it is recommended to
arrange for the service and maintenance engineer to check the appliance on
both the water and gas side within three months following installation. Based on
this check, the best maintenance frequency can be determined.
Note
Regular maintenance extends the service life of the appliance.
Note
Both the end user and the service and maintenance engineer are
responsible for regular maintenance. They will need to establish clear
agreements on this.
Note
If the appliance is not regularly maintained, the warranty will become void.
1.6 Forms of notation The following notation is used in this manual:
Note
Important information.
Caution
Ignoring this information can lead to the appliance being damaged.
Warning
Failure to carefully read this information may lead to personal injury and
serious damage to the appliance.
Symbol Target group
(End) user
Installation engineer
Service and maintenance engineer

Instruction manual SGS 11
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1.7 Overview of this
document
Chapter Target groups Description
Working principle of the
appliance
This chapter describes the working principle of the
appliance.
Installation This chapter describes the installation activity to be
completed before you start the appliance for the first time.
Conversion to a different gas
category
This chapter describes the activities required to convert
the appliance to a different gas category.
Filling This chapter describes how to fill the appliance.
Draining This chapter describes how to drain the appliance.
The control panel This chapter describes the general control of the
appliance using the display.
Status of the appliance This chapter describes the status (mode or condition) that
the appliance may have, and possible actions to take.
Starting and running This chapter describes how to start the appliance running.
The general heating cycle of the appliance is also
described.
Shutting down This chapter describes how to shut the appliance down for
a brief or long period of time.
Main menu This chapter describes the main menu of the display. This
is the actual menu for the user, however the installation
engineer and service and maintenance engineers will also
need to use this menu.
Service program This chapter describes the service menu. It is mainly
intended for the installation engineer and service and
maintenance engineers. End users may also refer to this
chapter for additional information about the appliance.
Troubleshooting This chapter is mainly intended for the installation
engineer and the service and maintenance engineer. It
describes appliance errors. These errors are indicated on
the display. A troubleshooting table of possible causes
and solutions is provided. End users may also refer to this
chapter for additional information about the appliance.
Maintenance frequency This chapter describes how to determine the optimum
frequency at which to carry out maintenance. Both the
end user and the service and maintenance engineer are
responsible for regular maintenance. They need to reach
clear agreement on this.
Note
If the appliance is not regularly maintained, the
warranty will become void.
Performing maintenance This chapter sets out the maintenance tasks to be carried
out during a service.
Warranty (certificate) This chapter states the warranty terms and conditions.

Introduction
12 Instruction manual SGS
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Instruction manual SGS 13
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2 Working principle of
the appliance
2.1 Introduction Topics covered in this chapter:
•General working principle of the appliance;
•The appliance's heating cycle;
•Protection for the appliance;
•Safety of the installation;
•Protection for the solar heating system.
2.2 General working
principle of the
appliance
The figure shows a cut-away view of the appliance.
In this appliance, the cold water enters the bottom of the tank through the cold
water inlet (14).
Once the appliance and the storage reservoir are completely filled with water,
they are both constantly under mains water pressure. When hot water is drawn
from the appliance, it is immediately replenished with hot water from the storage
tank, which in turn is replenished with cold water. The water in the storage tank
is heated by a heat exchanger which is connected to the solar heating system.
The appliance is equipped with a gas/air premix burner (17). The air is drawn in
through the fan (18). The gas is supplied via the gas control (16) on the intake
side of the fan. The gas/air mixture is then blown into the burner. The modulated
supply of gas and air ensures that the optimum gas/air mixture is always
achieved.
A gas-fired heat exchanger (11) in the appliance heats the tap water further if
necessary. The air required by the latter for combustion is forced into the burner
(17) by the fan (18).
The heated tap water leaves the tank through the hot water outlet (2). Once the
appliance is completely filled with water, it will constantly be under mains water
pressure. When hot water is drawn from the appliance, it is immediately
replenished with cold water.
The gas is fed to the burner via the gas control (16). The modulated supply of
gas and air ensures that the optimum gas/air mixture is always achieved. The
special construction of the burner causes the mixture to form a vortex (cyclone
effect) before it becomes ignited. This vorticity improves the ignition on the hot
surface igniter (20), as well as ensuring optimum combustion efficiency. The
special design of the heat exchanger (11) ensures that the flue gases are first
led downwards via the combustion chamber, then upwards via the heat
exchanger, and downwards again alongside the water in the tank. The flue
gases gradually become cooler in the process. Because the cooled flue gases
flow alongside the cold water lower down in the tank, they start to condense.
This condensation causes latent heat energy to be transferred to the cooler
water, thereby increasing the performance of the unit. The condensate yielded
by this process is discharged via the siphon (23).
Heat losses are prevented by the insulating layer (24) in both the storage tank
and the appliance itself. Both are enamel-coated on the inside to protect against
corrosion. The anodes (9) provide extra protection against corrosion. Both are
fitted with an inspection and cleaning opening (12) for maintenance purposes.

Working principle of the appliance
14 Instruction manual SGS
2gis
Cut-away view of the appliance
2.3 The appliance's
heating cycle The net water temperature (Tnet) in the appliance is used to regulate when both
the gas burner and the solar heating system are started and stopped. Tnet is the
curve shown in the figure. The controller uses two measured values to calculate
this temperature: T1(7) and T2(13). In addition, temperatures S1, S2and S3
are used by the controller of the solar heating system. S1is measured in the
solar collector. S2is located between the inlet and outlet of the heat exchanger
of the storage tank. S3is measured at the top side of the storage tank.
Depending on whether or not hot water is being drawn off, hot water can be
pumped from the storage tank to the appliance. This happens when S3is 5 oC
higher than Tnet. Water is then pumped from the appliance to the storage tank,
causing hot water to flow from the storage tank into the appliance. The pump
switches off as soon as S3equals Tnet.
The other settings that govern the control behaviour are:
•T
set
Tset is the the required water temperature that has been set on the
appliance (11.4.1 "Setting the water temperature via the SET POINT
MENU"). As soon as Tnet falls below Tset, the water heating via the solar
heating system is started, however, only if the temperature of the heating
Legend
Only applicable numbers are
mentioned.
1. cover
2. hot water outlet
3. electrical connector block
4. electronic controller
5. pressure switch
6. control panel
7. temperature sensor T1
8. combustion chamber
9. anode
10. tank
11. heat exchanger
12. inspection and cleaning opening
13. temperature sensor T2
14. cold water inlet
15. drain valve
16. gas control
17. burner
18. fan
19. air supply hose
20. hot surface igniter
21. flame probe
22. chimney pipe
23. siphon
24. insulation layer
25. mains power choke
26. EMC filter
27. frequency controller
28. potentiostat
29. pallet
IMD-
0
21
9
R2
1
25
19
16
10
11
22
23
5
9
26
27
28
2
4
7
6
3
8
18
20
21
17
12
13
14
15
24
29

Instruction manual SGS 15
gis
fluid (S1) is a certain (adjustable) value higher than the temperature
measured at the appliance (sensor S2). As soon as (Tnet = Tset = Tsolar limit),
heating via the solar heating system is stopped. There is one exception to
this rule, and that is when Tsolar limit is set to a higher value than Tset.
• Hysteresis
The moment Tnet falls below (Tset - Tsolar diff - Hysteresis), the controller
registers such a heat demand that the gas burner and the solar heating
system jointly heat the water. The solar heating system is only employed
when the temperature measured by S1is a certain (adjustable) value grater
than that of S2.
•T
solar diff
When Tnet exceeds (Tset - Tsolar diff), the gas burner is shut off and the water
is heated exclusively by the solar heating system. When Tnet rises above
Tset (provided Tset = Tsolar limit), the solar heating system switches off. The
value of Tsolar diff is adjustable (12.8.5 "Setting the solar difference").
•T
solar limit
Preset (12.8.4 "Setting the solar limit temperature") water temperature at
which heating via the solar heating system is stopped.
Graphical representation of heating cycle
Note
Tnet can rise above Tset,. However, this is only possible if Tsolar limit is
increased via the service menu.
Note
Tsolar limit can be lower than Tset; this will mean that Tnet can never be equal
to Tset.
2.4 Protection for the
appliance
2.4.1 Introduction
The electronic controller monitors the water temperature, helps ensure the safe
use of the solar heating system, and ensures safe combustion. This takes place
using:
•theAppliance water temperature protection
•theGas valve
•theFan
•thePressure switch
•theFlame probe
Legend
A = Gas burner on
B = Gas burner off
Tnet:
• = no heat demand, so water
not heated
• = water heated via solar
heating system
• = water heated via solar
heating system and gas burner
t = time
T = Temperature
45 oC = Minimum tap water
temperature
T
solar limit
T
set
Solar diff.
Hys.
T
min = 45C

Working principle of the appliance
16 Instruction manual SGS
2gis
2.4.2 Appliance water temperature protection
The electronic controller uses temperature sensors T1(7) and T2to monitor
several temperatures that are important for safety.
The table explains the functioning of these temperature sensors.
Temperature protection
2.4.3 Water temperature protection for the storage tank
Using temperature sensors S2and S3, the solar heating system controller
monitors several temperatures in the storage tank that are related to safety.
Temperature protection
2.4.4 Gas valve
The electronic controller opens the gas valve so that gas can be supplied to the
burner. As a safety measure, the gas valve has a double shut-off. The double
shut-off guarantees complete isolation of the appliance from the gas supply.
To help ensure smooth ignition, the gas valve opens gradually ('softlite").
2.4.5 Fan
The fan (18) provides an optimum air supply when there is a heat demand. As
a safety feature, the fan ensures that any gases present in the combustion
chamber are removed, both before and after combustion. We refer to this as
pre- and post-purge.
The fan speed is continuously monitored by the electronic controller (4). The
electronic controller takes control if the speed of rotation varies too much from
the set value.
Protection Description
Against frost:
- T1< 5°C
- T2< 5°C
The frost protection cuts in. The water is heated to 20°C.
For maximum water temperature:
- T1 > 85°C
- T2> 85°C
The high-limit safeguard serves to prevent overheating and/or excessive
formation of scale in the appliance. If the high-limit safeguard is activated, the
heating is stopped. This causes the water in the tank to cool down. Once the
water has cooled sufficiently (T1< 78°C), the electronic controller resets the
appliance.
For extra safety:
- T1> 93°C
- T2> 93°C
A lockout error of the water heater controller takes place. The controller must
be manually reset before the appliance can resume operation (8.4 "Error
conditions"). The reset may only be performed if T1<78°C.
Protection Description
Against frost:
- S2, S3< 5°C
The frost protection cuts in. The water is heated to 20°C.
For maximum water temperature:
- S2, S3> 85°C
The high-limit safeguard serves to prevent overheating and/or excessive
formation of scale in the storage tank. If the high-limit safeguard is activated,
the heating is stopped. This causes the water in the storage tank to cool down.
Once the water has cooled sufficiently (S3< 78°C), the electronic controller
resets the appliance.
For extra safety:
- S2, S3> 93°C
A lockout error of the water heater controller takes place. The controller must
be manually reset before the appliance can resume operation (8.4 "Error
conditions"). The reset may only be performed if S3< 78°C.

Instruction manual SGS 17
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2.4.6 Pressure switch
The pressure switch ensures the discharge of flue gases and the supply of
incoming air during the pre-purge and normal running of the appliance. The
default state of the pressure switch is open. When sufficient pressure difference
is reached, the pressure switch closes. However, in the event of a fault, the
pressure switch is tripped open, and the heating cycle is interrupted. The table
shows the trip point per appliance.
Note
The trip point of the pressure switch is not adjustable.
Pressure switch trip points
2.4.7 Flame probe
To ensure that no gas can flow when there is no combustion, the water heater is
fitted with a flame probe (21). The electronic controller uses this probe to detect the
presence of a flame, by means of ionisation detection. The electronic controller
closes the gas control the instant it detects that there is a gas flow but no flame.
2.5 Safety of the
installation
In addition to the appliance's standard built-in safety monitoring, the appliance
must also be protected by an expansion vessel, expansion valve, pressure
reducing valve, non-return valve and a T&P valve.
The use of an expansion vessel, expansion valve and/or pressure reducing
valve depends on the type of installation: unvented or vented.
2.5.1 Unvented installation
With an unvented installation, an expansion valve valve and expansion vessel
prevent the buildup of excessive pressure in the tank. This prevents damage
being caused to the enamelled coating (in the appliance) or to the tank. A non-
return valve prevents excessive pressure buildup in the water supply system.
This valve also prevents water from flowing backwards from the tank into the
cold water supply system. The pressure reducing valve protects the installation
against an excessively high water supply pressure (> 8 bar). These components
are fitted to the cold water pipe (3.6 "Water connections, Vented").
2.5.2 Vented installation
With a vented installation, excess pressure is taken up by the open cold water
head tank. The height of the head tank determines the working pressure in the
water heater, which may not exceed 8 bar. The installation must also be fitted
with a vent pipe from the hot water pipe, that opens into the cold water tank.
Ideally, the vent pipe should discharge into a separate tundish/drain or
otherwise to the open cold water head tank. The water heater should also be
fitted on the hot water side with a stop valve (3.7.2 "Hot water side").
2.5.3 T&P valve
A T&P valve is only mandatory in an unvented installation. However, A.O. Smith
also recommends the use of a T&P valve in vented installations.
A T&P (Temperature and Pressure Relief) valve monitors the pressure in the
tank and the water temperature at the top of the tank. If the pressure in the tank
becomes excessive (> 10 bar) or the water temperature is too high (> 97°C), the
valve will open. The hot water can now flow out of the tank. Because the
Appliance Closing pressure difference Opening pressure difference
SGS 80 > 1005 Pa < 975 Pa
SGS 100 > 1145 Pa < 1115 Pa

Working principle of the appliance
18 Instruction manual SGS
2gis
appliance is under water supply pressure, cold water will automatically flow into
the tank. The valve remains open until the unsafe situation has been rectified.
The appliance is fitted standard with a connecting point for a T&P
valve (3.7.2 "Hot water side").
2.5.4 Protection for the solar heating system
Drain-back tank
The solar heating system may optionally be equipped with a drain-back tank.
The tank fills itself with the heating fluid when there is no heat demand. This
avoids overheating of the solar heating system. The high insulation factor of the
tank also protects the system from freezing of the fluid. The use of the drain-
back tank also serves to extend the useful life of the fluid.
The presence of a drain-back tank is set (12.8.1 "Setting the drain-back tank")
during the installation. Refer to the solar heating system manual for more
details.
Fluid temperature
The heat exchanger of the solar heating system may be filled with glycol. If the
temperature of the heating fluid is too high, a signal is sent to the controller of
the solar collector and the pump of the solar collector is switched off. This signal
is passed to the controller by temperature sensor S1.
At present, no heating fluids other than glycol are supported. The heating fluid
type is set (12.8.2 "Setting the heating fluid type in the solar heating system")
during installation.
Temperature protection for solar heating system
2.5.5 Safety of the solar heating system
Expansion vessel
The solar heating system must be equipped with an expansion vessel (16). An
expansion vessel serves to limit pressure variations in the system. The
expansion vessel in the solar heating system can withstand a maximum
pressure of 6 bar. The supply pressure to the expansion vessel depends on the
static head of the system.
Besides the expansion vessel, the system is protected from overpressure by an
expansion valve ( "Expansion valve").
Expansion valve
The solar heating system is equipped with an expansion valve (23). The
expansion valve monitors the pressure in the solar heating system. If the
pressure is excessive (> 6 bar), then the valve will open. The hot water can now
flow out of the installation. The valve remains open until the unsafe situation has
passed, i.e. until the pressure has fallen back below 6 bar.
Note
Because the installation is always under pressure and is not automatically
filled, the system will again need to be replenished (5 "Filling").
Protection Description
Maximum temperature S1, if solar
heating system is filled with
glycol:
- S1> 130°C
The pump of the solar heating system
switches off when the temperature of the
heating fluid at S1exceeds the maximum
value. The solar heating system enters
error mode. The error is also visible on the
display of the SGS appliance

Instruction manual SGS 19
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3 Installation
Warning
Installation work should be carried out by an approved installation engineer
in compliance with the general and local regulations imposed by the gas, water
and power supply companies and the fire service.
The appliance may only be installed in a room that complies with the
requirements stated in national and local ventilation
regulations (1.3 "Regulations").
3.1 Introduction This chapter describes the installation activities to be carried out before you
actually start using the appliance (9 "Starting and running"), namely:
•Packaging;
•Environmental conditions;
•Technical specifications;
•Water connections, Vented;
•Water connections, Unvented;
•Water connections, Vented;
•Gas connection;
•Solar heating system;
•Air supply and flue;
•Electrical connection;
•Checking the supply pressure and burner pressure.
For conversion to a different gas category, see conversion (4 "Conversion to a
different gas category").
3.2 Packaging To avoid damaging the appliance, remove the packaging carefully.
We recommend unpacking the appliance at or near its intended location.
Caution
The appliance may only be manoeuvred in an upright position. Take care
that the appliance is not damaged after unpacking.
3.3 Environmental
conditions
The appliance is suitable for either open or room-sealed combustion. If
installed as a room-sealed appliance, then the availability of the necessary
external air supply will depend on the place of installation. In this event, there
are no additional ventilation requirements.
If the appliance is to be installed as an open system, then it will be subject to
the guidelines and ventilation regulations that are in force locally.
The alternative installation types are B23, C13, C33, C43, C53 and C63.
Caution
The appliance may not be used in rooms where chemical substances are
stored or used, due to the risk of explosion and/or corrosion of the appliance.
Some propellants, bleaching agents, degreasing agents etc. disperse vapours
which are explosive and/or which cause accelerated corrosion. If the appliance
is used in a room in which such substances are present, the warranty will be
void.

Installation
20 Instruction manual SGS
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3.3.1 Air humidity and ambient temperature
The boiler room must be frost-free, or be protected against frost. The table
shows the environmental conditions that must be adhered to for correct
functioning of the electronics present in the appliance to be guaranteed.
Air humidity and ambient temperature specifications
3.3.2 Maximum floor load
In regard to the total weight of the installation, bear in mind that the installation
always comprises an appliance complete with storage tank.
Maximum floor load
Allow for the appliance's weight with respect to the maximum floor load; refer to
the table.
Weight specifications related to maximum floor load
Maximum floor load of storage tank
Bear in mind the weight of the storage tank (completely filled with water) when
considering the maximum floor load. This maximum floor load may be between
400 and 4500 kg. This depends on the type of storage tank .
3.3.3 Water composition
The appliance is intended for heating drinking water. The drinking water must
comply with the regulations governing drinking water for human consumption.
The table gives an overview of the specifications.
Water specifications
Note
If the water specifications deviate from those stated in the table, the storage
tank protection cannot be guaranteed (16 "Warranty (certificate)").
If the water hardness is greater than 4° dH, please contact A.O. Smith.
Air humidity and ambient temperature
Air humidity max. 93% RV at +25°C
Ambient temperature Functional: 0 < T < 60°C
Weight of the appliance filled with water
SGS 80, SGS 100 940 kg
Water composition
Hardness
(alkaline earth ions)
> 1.00 mmol/l:
• German hardness > 5.6° dH
• French hardness > 10.0° fH
• British hardness > 7.0° eH
Conductivity > 125 µS/cm
Acidity (pH value) 7,0 < pH value < 9.5