A.O. Smith SGS-28 Troubleshooting guide

0311183
Innovation has a name.
Installation, User and Service
Manual
Condensing High Efficiency
Gas-Solar Water Heater
SGS - 28/30/50/60/80/100/120
SGS
3015 - Changes Reserved.

your installer
A.O. Smith UK, Unit B8 Amstrong Mall,
Southwood Business Park, Farnborough, Hampshire GU14 0NR
www.aosmith.co.uk
“A.O. Smith Water Heaters” is a trading name of Advance Services (Sales) Ltd. Reg.

E1
Errata
The amendments below apply to:
the preparation of the electrical connection of the solar heating control (3.12.1 "Preparation");
finishing maintenance (15.6 "Finalizing maintenance");
the electrical diagram of the solar heating control (17.4 "Electrical diagram solar heating system").
These instructions supersede the previous instructions of the solar heating control.
3.12.1 Preparation
Remove the cover (snap-on type) from the terminal block of the solar heating control.
This has the following terminals:
0311615 R0.0
15.6 Finalizing
maintenance
To finalize the maintenance, carry out the following steps:
1. Fill the water heater (5 "Filling").
2. Start the water heater (9 "Starting the water heater").
3. Check the CO2value (3.12.3 "CO2adjustment").
4. Check the switching pressure of the pressure switch. (3.12.4 "Switching pressure
measurement")
5. Erase the message SERVICE REQUIRED. The displayed message can be reset in
either of two ways:
Temporary reset: To postpone the message, press RESET once. The message
will reappear on the display 7 days later.
2.Full reset: To fully reset the message, press and hold both RESET and ENTER
at the same time for 5 sec.
On completion of the full reset of the message, the message below will appear on the
display. This message will NOT be shown after a temporary rest of the message.

E2
17.3 Electrical diagram Electrical diagram
solar heating
system
0309687b R2.0
1 = brown, 2 = blue, 3 = yellow / green, 4 = black, 5 = white, 6 = grey / beige, 7 = green, 8 = yellow

E3
TERMINAL BLOCK CONNECTIONS
Earth
N Neutral
L Live input of the controller
L3Live input for the solar heating system modulating pump
PWM+ PWM+ stuursignaal t.b.v. aansturing pomp zonnesysteem
PWM- PWM- stuursignaal t.b.v. aansturing pomp zonnesysteem
COMPONENTS
AA Controller
BB[VAC] Solar heating system pump (modulating) (230 VAC)
BB[PWM] Solar heating system pump (modulating) (PWM-signal)
CC Temperature sensor (S1- solar collector)
DD Temperature sensor (S2- tank)
EE Combined Q/T sensor
(incl. temperature sensor S4- solar collector return)
FF Communication between the water heater controller and the solar
Heating system controller (BUS-link)
GG Temperature sensor (S3- top of storage tank)
K Double-pole isolator
CONTROLLER CONNECTIONS
J12 Connection of combined Q/T sensor (1-2-3-4)
J13 Connection of temperature sensor S1(2-4)
J14 Connection of temperature sensor S2(2-4) and temperature sensor S3
(1-3)
J16 Connection of BUS-link communication
J18 Connection of PWM-signal solar heating system pump
F2 Fuse (T 3.15A - 250 V)

Instruction manual SGS 3
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Read this manual carefully Warning
Read this manual carefully before starting the water heater. Failure to read
the manual and to follow the printed instructions may lead to personal injury and
damage to the water heater.
Copyright © 2013 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 unauthorised use, use other than that stated in this manual,
and use other than in accordance with the General Conditions registered at the
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 specific aspects related to the
water heater, then please do not hesitate to contact:
A.O.Smith Water Products Company
PO Box 70
5500 AB Veldhoven
The Netherlands
Telephone: (free) 0870-AOSMITH
0870-2676484
General: [phone]
Fax: [phone]
E-mail: [e-mail]
Website: www.aosmith.co.uk
In the event of problems with your gas, electricity or water supply connections,
please contact the supplier/installation engineer of your installation.

4Instruction manual SGS
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Instruction manual SGS 5
Contents
1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - 9
1.1 About the water heater - - - - - - - - - - - - - - - - - - - - - - - - - - - 9
1.2 What to do if you smell gas- - - - - - - - - - - - - - - - - - - - - - - - - 9
1.3 Regulations - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9
1.4 Target groups - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10
1.5 Maintenance - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11
1.6 Notation conventions- - - - - - - - - - - - - - - - - - - - - - - - - - - 11
1.7 Overview of this document - - - - - - - - - - - - - - - - - - - - - - - - 12
2 Working principle of the water heater - - - - - - - - - - - - - 13
2.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 13
2.2 General working principle of the water heater - - - - - - - - - - - - - - - 13
2.3 Water heater operating cycle - - - - - - - - - - - - - - - - - - - - - - - 15
2.4 Protection for the water heater - - - - - - - - - - - - - - - - - - - - - - 16
2.5 Safety of the installation - - - - - - - - - - - - - - - - - - - - - - - - - 17
2.6 Protection for the solar heating system - - - - - - - - - - - - - - - - - - 18
2.7 Safety of the solar heating system - - - - - - - - - - - - - - - - - - - - 19
3 Installation - - - - - - - - - - - - - - - - - - - - - - - - - - - 21
3.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 21
3.2 Packaging - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 21
3.3 Ambient conditions- - - - - - - - - - - - - - - - - - - - - - - - - - - - 21
3.4 Technical specifications - - - - - - - - - - - - - - - - - - - - - - - - - 23
3.5 Installation diagram - - - - - - - - - - - - - - - - - - - - - - - - - - - 29
3.6 Unvented water connections - - - - - - - - - - - - - - - - - - - - - - - 30
3.7 Vented water connections - - - - - - - - - - - - - - - - - - - - - - - - 30
3.8 Gas connection - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 31
3.9 Solar heating system- - - - - - - - - - - - - - - - - - - - - - - - - - - 32
3.10 Air supply and chimney flue discharge - - - - - - - - - - - - - - - - - - 32
3.11 Electrically connecting the water heater- - - - - - - - - - - - - - - - - - 38
3.12 Electrical connection of the solar heating system - - - - - - - - - - - - - 42
3.13 Check the supply pressure, gas control valve pressure, CO2value and
switching pressure - - - - - - - - - - - - - - - - - - - - - - - - - - - - 45
4 Conversion to a different gas category - - - - - - - - - - - - 53
4.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 53
5 Filling - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 55
5.1 Filling unvented installations - - - - - - - - - - - - - - - - - - - - - - - 55
5.2 Filling vented installations - - - - - - - - - - - - - - - - - - - - - - - - 56
5.3 Filling solar heating system- - - - - - - - - - - - - - - - - - - - - - - - 56
6 Draining - - - - - - - - - - - - - - - - - - - - - - - - - - - - 59
6.1 Draining unvented installations - - - - - - - - - - - - - - - - - - - - - - 59
6.2 Draining vented installations - - - - - - - - - - - - - - - - - - - - - - - 60
6.3 Draining solar heating system - - - - - - - - - - - - - - - - - - - - - - 60
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Contents
6Instruction manual SGS
7 The control panel - - - - - - - - - - - - - - - - - - - - - - - - 63
7.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 63
7.2 Control - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 63
7.3 Explanation of icons- - - - - - - - - - - - - - - - - - - - - - - - - - - - 63
7.4 ON/OFF switch on controller - - - - - - - - - - - - - - - - - - - - - - - 63
7.5 Navigation buttons - - - - - - - - - - - - - - - - - - - - - - - - - - - - 63
7.6 PC connection - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 64
8 Status of the water heater - - - - - - - - - - - - - - - - - - - 65
8.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 65
8.2 Operating modes - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 65
8.3 Error conditions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 66
8.4 Service condition - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 67
8.5 Anode warning - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 67
8.6 Q/T Sensor warning - - - - - - - - - - - - - - - - - - - - - - - - - - - - 67
8.7 Collector temperature warning- - - - - - - - - - - - - - - - - - - - - - - 67
9 Starting the water heater - - - - - - - - - - - - - - - - - - - - 69
9.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 69
9.2 Starting the appliance - - - - - - - - - - - - - - - - - - - - - - - - - - - 69
9.3 The appliance's heating cycle - - - - - - - - - - - - - - - - - - - - - - - 69
10 Shutting down - - - - - - - - - - - - - - - - - - - - - - - - - 71
10.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 71
10.2 Decommissioning the water heater for a short period- - - - - - - - - - - - 71
10.3 Isolating the water heater from the mains - - - - - - - - - - - - - - - - - 71
10.4 Decommissioning the water heater for a long period - - - - - - - - - - - - 71
11 Main menu - - - - - - - - - - - - - - - - - - - - - - - - - - - 73
11.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 73
11.2 Notation convention for menu-related instructions - - - - - - - - - - - - - 73
11.3 Switching to "ON mode" - - - - - - - - - - - - - - - - - - - - - - - - - - 73
11.4 Setting the water temperature - - - - - - - - - - - - - - - - - - - - - - - 73
11.5 Week program - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 74
11.6 Starting and stopping the week program - - - - - - - - - - - - - - - - - - 74
11.7 Changing the appliance's standard week program - - - - - - - - - - - - - 74
11.8 Adding times to a week program- - - - - - - - - - - - - - - - - - - - - - 76
11.9 Deleting times from a week program- - - - - - - - - - - - - - - - - - - - 77
11.10 Extra period- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 78
11.11 Settings- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 79
12 Service program - - - - - - - - - - - - - - - - - - - - - - - - 81
12.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 81
12.2 Setting the hysteresis - - - - - - - - - - - - - - - - - - - - - - - - - - - 81
12.3 Displaying the error history - - - - - - - - - - - - - - - - - - - - - - - - 81
12.4 Displaying the water heater history - - - - - - - - - - - - - - - - - - - - 81
12.5 Display the selected water heater - - - - - - - - - - - - - - - - - - - - - 82
12.6 Setting the service interval - - - - - - - - - - - - - - - - - - - - - - - - 82
12.7 Service mode - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 82
12.8 Setting legionella prevention- - - - - - - - - - - - - - - - - - - - - - - - 83
12.9 Solar heating system configuration - - - - - - - - - - - - - - - - - - - - 83
12.10 Setting the central heating configuration - - - - - - - - - - - - - - - - - - 84

Instruction manual SGS 7
13 Errors- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 85
13.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 85
13.2 Troubleshooting table for general errors - - - - - - - - - - - - - - - - - 86
13.3 Troubleshooting table for displayed errors - - - - - - - - - - - - - - - - 89
13.4 Warnings on the display - - - - - - - - - - - - - - - - - - - - - - - - - 98
14 Service interval - - - - - - - - - - - - - - - - - - - - - - - - - 99
14.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 99
14.2 Determining service interval - - - - - - - - - - - - - - - - - - - - - - - 99
15 Performing maintenance - - - - - - - - - - - - - - - - - - - - 101
15.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 101
15.2 Preparation for maintenance - - - - - - - - - - - - - - - - - - - - - - - 101
15.3 Water-side maintenance - - - - - - - - - - - - - - - - - - - - - - - - - 102
15.4 Gas-side maintenance - - - - - - - - - - - - - - - - - - - - - - - - - - 103
15.5 Solar collector maintenance - - - - - - - - - - - - - - - - - - - - - - - 104
15.6 Finalizing maintenance- - - - - - - - - - - - - - - - - - - - - - - - - - 104
16 Warranty (certificate) - - - - - - - - - - - - - - - - - - - - - - 105
16.1 General warranty - - - - - - - - - - - - - - - - - - - - - - - - - - - - 105
16.2 Tank warranty - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 105
16.3 Conditions for Installation and use - - - - - - - - - - - - - - - - - - - - 105
16.4 Exclusions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 106
16.5 Scope of the warranty - - - - - - - - - - - - - - - - - - - - - - - - - - 106
16.6 Claims - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 106
16.7 Obligations of A.O.Smith - - - - - - - - - - - - - - - - - - - - - - - - - 106
17 Appendices- - - - - - - - - - - - - - - - - - - - - - - - - - - 107
17.1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 107
17.2 Menu structure- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 108
17.3 Electrical diagram for the appliance- - - - - - - - - - - - - - - - - - - - 110
17.4 Electrical diagram, solar heating system - - - - - - - - - - - - - - - - - 112
17.5 Declaration of conformity - - - - - - - - - - - - - - - - - - - - - - - - - 114
17.6 Week program card - - - - - - - - - - - - - - - - - - - - - - - - - - - 115

Contents
8Instruction manual SGS

Instruction manual SGS 9
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1 Introduction
1.1 About the water
heater
This manual describes how to install, service and use the SGS water heater.
The SGS water heater is a condensing boiler with a fan in the air intake. The
water heater is typically supplied with a storage tank fitted with a heat
exchanger connected to a solar energy source, but can also operate standalone.
The SGS can be installed as either an open or room-sealed water heater. A
concentric chimney connector is fitted standard to the water heater, but a
parallel system can also be connected.
The possible installation types are B23, C13, C33, C43, C53 and C63.
The information in this manual applies to types: SGS 28, SGS 30, SGS 50,
SGS 60, SGS 80, SGS 100 and SGS 120.
The water heater 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 water heaters are therefore compliant with the
European Directive for Gas water heaters, and and are entitled to bear the CE
mark.
Warning
Read this manual carefully before starting the water heater for the first time.
Failure to read the manual and to follow the printed instructions may lead to
personal injury and damage to the water heater.
1.2 What to do if you
smell gas
Warning
If you smell gas:
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 Gas Safety (installations and Use) Regulations 1998 (as amended). It is law
that all gas appliances are installed by competent persons, in accordance with
the above regulations. Failure to install appliances correctly could lead to
prosecution. It is in your own interest and that of safety, to ensure that this law
is complied with.
The installation of the water heater MUST be in accordance with the relevant
requirements of the Gas Safety Regulations, Building Regulations, IEE
Regulations and the Water Supply (water fittings) Regulations.
0063

Introduction
10 Instruction manual SGS
1gis
The installation should also be in accordance with any relevant requirements of
the HSE, local gas region and local authority and the relevant recommendations
of the following documents:
British and European Standards
•BS 6891:
Installation of low pressure gas pipework of up to 35 mm (R1¼) in domestic
premises (2nd family gas) - Specification. Note: for lager installations see
IGE/UP/2 below.
•BS 6798:
Specification for installation and maintenance of gas-fired boilers of rated
input not exceeding 70 kW net.
•BS 6644:
Specification for installation of gas-fired hot water boilers of rated inputs
between 70 kW (net) and 1.8 MW (net) (2nd and 3rd family gases).
•BS 6700:
Design, installation, testing and maintenance of services supplying water for
domestic use within buildings and their cartilages - Specifications
•BS EN 806-2:
Specification for installations inside buildings conveying water for human
consumption. Part 2: Design.
•BS 5546:
Specification for installation of hot water supplies for domestic purposes,
using gas-fired appliances of rated input not exceeding 70 kW.
•BS 5440:
Flueing and ventilation for gas appliances of rated input not exceeding 70
kW net (1st, 2nd and 3rd family gases).
Part 1: Specification for installation of gas appliances to chimneys and for
maintenance of chimneys.
Part 2: Specification for installation and maintenance of ventilation for gas
appliances.
Institute of Gas Engineers and Managers (IGEM) Publications
•IGE/UP/1:
Soundness testing and purging of industrial and commercial gas
installations.
•IGE/UP/1A:
Soundness testing and direct purging of small low pressure industrial and
commercial natural gas installations.
•IGE/UP/2:
Gas installation pipework, boosters and compressors on industrial and
commercial premises.
•IGE/UP/10:
Installation of flued gas appliances in industrial and commercial premises.
CIBSE Publications
•Guide G: Public Health Engineering.
1.4 Target groups The three target groups for this manual are:
• (end) users;
• installation engineers;
• service and maintenance engineers.

Instruction manual SGS 11
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Symbols on each page indicate the target groups for whom the information is
intended. See the table.
Target group symbols
Caution
This water heater is not intended for use by persons with reduced physical,
sensory or mental capacities, or who lack the necessary experience or
knowledge, unless the person responsible for their safety is supervising them or
has explained to them how the water heater should be used.
Caution
This water heater is not intended to be used by children. Always supervise
children, and ensure that they do not play with the water heater.
1.5 Maintenance A service should be carried out at least once a year, both on the water side and
on the gas side. Among other things, the service interval depends on the water
quality, the average burning time per day and the set water temperature.
Note
To determine the correct service interval, it is recommended to arrange for
the service and maintenance engineer to check the water heater on both the
water and gas side within three months following installation. Based on this
check, the best service interval can be determined.
Note
Regular maintenance extends the service life of the water heater.
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 water heater is not regularly serviced, the warranty will become void.
1.6 Notation
conventions
The following notation is used in this manual:
Note
Important information.
Caution
Ignoring this information can lead to the water heater being damaged.
Warning
Failure to carefully read this information may lead to danger of personal
injury, and serious damage to the water heater.
Symbol Target Group
(End) user
Installation engineer
Service and maintenance engineer

Introduction
12 Instruction manual SGS
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1.7 Overview of this
document
Chapter Target groups Description
Working principle of the water
heater
This chapter describes the working principle of the water
heater.
Installation This chapter describes the installation activities to be
carried out before final commissioning.
Conversion to a different gas
category
This chapter describes the activities required to convert
the water heater to a different gas category.
Filling This chapter describes how to fill the water heater.
Draining This chapter describes how to drain the water heater.
The control panel This chapter describes the general control of the water
heater using the display.
Status of the water heater This chapter describes the status (mode or condition) that
the water heater may have, and possible actions to take.
Starting the water heater This chapter describes how to start the water heater. The
general operating cycle of the water heater is also
described.
Shutting down This chapter describes how to decommission the water
heater 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 water heater.
Errors This chapter is mainly intended for the installation
engineer and the service and maintenance engineer. It
describes water heater errors. These errors are reported
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 water heater.
Service interval This chapter describes how to determine the optimum
service interval (frequency of regular 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 water heater is not regularly serviced, the
warranty will become void.
Performing maintenance This chapter sets out the maintenance tasks to be carried
out.
Warranty (certificate) This chapter states the warranty terms and conditions.

Instruction manual SGS 13
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2 Working principle of
the water heater
2.1 Introduction This chapter covers the following topics:
• General working principle of the water heater;
• Water heater operating cycle;
• Protection for the water heater;
• Safety of the installation;
• Protection for the solar heating system;
• Safety of the solar heating system.
2.2 General working
principle of the water
heater
In this water heater, the cold water enters the bottom of the tank through the cold
water inlet (14).
Once the water heater and the storage reservoir are completely filled with water,
they are both constantly under mains water pressure. When hot water is drawn
from the water heater, 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 water heater is fitted with a modulating premix burner system with 1:1 gas-
to-air ratio regulation. The air required for combustion is delivered by the fan
(18). The gas is supplied via the gas control valve (16) and the venturi (30) on
the intake side of the fan. The 1:1 gas-to-air ratio always guarantees the most
efficient gas/air mixture.
The heated tap water leaves the tank through the hot water outlet (2).
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 condens trap (23).
Heat losses are prevented by the insulating layer (24) in both the storage tank
and the water heater 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.

14 Instruction manual SGS
Cut-away view of the water heater
Legend SGS 28, 30, 50, 60 SGS 80, 100, 120
Unused numbers are not applicable
1. cover
2. hot water outlet
3. electrical connector block
4. 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 valve
17. burner
18. fan
19. air supply hose
20. hot surface igniter
21. flame probe
22. chimney pipe
23. condens trap
24. insulation layer
28. potentiostat
29. base
30. venturi
58. flue gas test point
59. pressure-reducing valve

Instruction manual SGS 15
gis
2.3 Water heater
operating cycle
The water temperature (T 1) at the top of the water heater is used to control
when the gas burner is started and stopped. The temperature changes in the
water heater are used for switching the solar heating system on and off (using
T1and S2). T1is 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 S2are used by the solar heating system controller. S1
is 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 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 water heater. This happens if S3is 5oC
higher than Ttop (T1). Water is then pumped from the water heater to the storage
tank, causing hot water to flow from the storage tank into the water heater. The
pump switches off as soon as S3is equal to T1.
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 T1falls below Tset, the solar heating system starts
heating the water, but only if the temperature of the heating fluid (S1) is
greater than the temperature measured at the appliance (sensor S2) by a
given (adjustable) amount. When T1= Tset = Tsolar limit, heating by the solar
heating system stops. There is one exception to this rule, which is when
Tsolar limit is set to a higher value than Tset.
• Hysteresis
The moment that T1falls 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 by the solar heating system alone. When T1rises above Tset
(provided that Tset = Tsolar limit), the solar heating system is switched off. The
value of Tsolar diff is adjustable (12.9.4 "Setting the solar difference").
•T
solar limit
Preset (12.9.3 "Setting the solar limit") water temperature at which heating
via the solar heating system is stopped.

Working principle of the water heater
16 Instruction manual SGS
2gis
Graphical representation of operating cycle
Note
T1can rise above Tset. However, this is only possible if Tsolar limit is increased
via the service menu.
2.4 Protection for the
water heater
2.4.1 Introduction
The controller monitors the water temperature, helps ensure the safe use of the
solar heating system, and ensures safe combustion. This takes place using:
• the Appliance water temperature protection
• the Storage tank water temperature protection
• the Gas control valve
• the Fan
• the Pressure switch
• the Flame probe
2.4.2 Appliance water temperature protection
The controller uses temperature sensors T1and T2to monitor several
temperatures that are important for safety.
The table explains the functioning of these temperature sensors.
Temperature protection
Legend
A = Gas burner on
B = Gas burner off
T1:
• = No heat demand, so water
is 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
Safety Description
Anti-frost:
- T1< 5°C
- T2< 5°C
The frost protection cuts in. The water is heated to 20°C.
At the maximum water
temperature:
- T1> 88°C
- T2> 88°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,
heating is stopped. This causes the water in the tank to cool down. Once the
water has cooled sufficiently (T1< 81°C), the 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 (8.3 "Error
conditions"). The reset may only be performed if T1< 81°C.

Instruction manual SGS 17
gis
2.4.3 Storage tank water temperature protection
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 control valve
The controller opens the gas control valve so that gas can be supplied to the
burner. As a safety measure, the gas control valve has two valves. Both valves
shut off the gas supply.
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 controller (4). The controller
takes control if the fan rpm varies too much from the value set.
2.4.6 Pressure switch
The pressure switch only guarantees the supply of air during pre-purging of the
water heater. If the pressure difference during pre-purging is sufficient, the
pressure switch closes. The table (3.4.2 "General and electrical specifications")
shows the trip point for each water heater.
Note
The trip point of the pressure switch is not adjustable.
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 controller uses this probe to detect the
presence of a flame, by means of ionisation detection. The controller closes the
gas control valve the instant it detects that there is a gas flow but no flame.
2.5 Safety of the
installation
Excessive pressure in the tank can damage the enamelled layer (in the water
heater) or the tank itself. An inlet combination and pressure-reducing valve
prevents this. The inlet combination acts as a stop valve, non-return valve and
overflow valve. If the water mains pressure is too high (3.4.2 "General and
electrical specifications"), a pressure-reducing valve must be used. Both
components must be fitted in the cold water inlet (3.7 "Vented water
connections").
The use of an expansion vessel, expansion valve and/or pressure reducing
valve depends on the type of installation: unvented or vented.
Protection Description
Against frost:
- S2, S3< 5°C
The frost protection cuts in. The water is heated to 20°C.
Against overheating of water:
- 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 controller resets the
water heater.