Riello TAU 150 N Guide

INSTALLATION, OPERATION, MAINTENANCE
AND SYSTEM MANAGEMENT MANUAL
STAINLESS STEEL
CONDENSING
BOILER
150 N ÷ 1450 N
150 NC ÷ 600 NC
TAU

2
TAU boilers conform to the Efficiency Directive 92/42/EEC ( ),
to Gas Directive 90/396/EEC and applicable sections of the Electromagnetic
Compatibility Directive 89/336/EEC and Low Voltage Directive 73/23/EEC.
0694
MODEL CODE
TAU 150 N 4031860.0
TAU 210 N 4031861.0
TAU 270 N 4031862.0
TAU 350 N 4031863.0
TAU 450 N 4031864.0
TAU 600 N 4031865.0
TAU 800 N 4031866.0
TAU 1000 N 4031867.0
TAU 1250 N 4031868.0
TAU 1450 N 4031869.0
MODEL CODE
TAU 150 NC 4031835.0
TAU 210 NC 4031836.0
TAU 270 NC 4031837.0
TAU 350 NC 4031838.0
TAU 450 NC 4031839.0
TAU 600 NC 4031849.0
CONFORMITY
RANGE

3
Dear Customer,
Thank you for choosing a rTAU stainless steel condensing boiler. You have purchased a
quality, high efficiency boiler that will give you dependable and safe service and provide comfort
in the home for many years to come. Arrange for your boiler to be serviced regularly by an autho-
rised rTechnical Assistance Centre. Their personnel are specially trained to keep your boiler
efficient and cheap to run. Technical Assistance Centres also stock any original spare parts that
might be required.
This instruction manual contains important instructions and precautions that must be observed to
ensure the trouble-free installation and efficient functioning of your rTAU boiler.
Please accept our renewed thanks for your purchase.
Riello S.p.A.
On request, your Technical Assistance Centre will also provide you with a system service book. In Italy this is required
by Presidential Decree n° 412 of the 26th August 1993. Your Technical Assistance Centre will also be pleased to instruct
you how to get the best from your new boiler.

This manual, Code 20014315 - Rev. 11 (02/10) is made
up of 44 pages
CONTENTS
4
The following symbols are used in this manual:
b CAUTION! = Indicates actions that require cau-
tion and adequate preparation
aSTOP! = Identifies actions that you MUST NOT do
GENERAL Page
General safety information 5
Safety precautions 5
Product description 6
Control panels 7
Recommended burners 7
Product identification 8
Accessories 9
Technical specifications 9
SYSTEM MANAGER
Initial start-up 10
Preparing for extended periods of disuse 11
Cleaning 12
Maintenance 12
Useful information 13
INSTALLER
Unpacking the product 14
Overall dimensions and weights 15
Handling 15
Place of installation 16
Water in the central heating circuit 17
Water connections 21
Condensate drain 25
Condensate neutralisation 25
Combustion gas exhaust 27
Door hinges 27
Changing the direction of door opening 28
Removing the hinge assembly “B” 29
Fitting the panelling 30
TECHNICAL ASSISTANCE SERVICE
Preparing for initial start-up 31
Initial start-up 32
Checks during and after initial start-up 33
Maintenance 34
- Opening the door 34
- Adjusting the door 34
Cleaning the boiler 35
Troubleshooting 36
APPENDIX
Water treatment in domestic heating systems
(extract from Italian standard UNI 8065) 37
CONTENTS

GENERAL 5
TAU boilers are delivered in separate crates. Check
that the appliance is complete and undamaged as
soon as you receive it. Report any discrepancies
or damage to the rdealer who sold it.
This rTAU boiler must be installed by a legally
qualified installer. (In Italy, the law regulating profes-
sional installers is Law 46 of the 5th March 1990.)
On completion of the installation, the installer must
issue the owner with a declaration of conformity
confirming that the installation has been completed
to the highest standards in compliance with the
instructions provided by rin this instruction
manual, and that it conforms to all applicable laws
and standards.
This boiler must only be used for the purpose spe-
cified by rand for which it is designed. r
declines all responsibility, contractual or other, for
damage to property or injury to persons or animals
caused by improper installation, adjustment, main-
tenance or use.
If you notice any water leaking from the boiler, imme-
diately disconnect it from the mains electricity supply,
shut off the water supply, and notify r’s Technical
Assistance Service or a qualified technician.
Periodically check that operating pressure in the
heating circuit is over 1 bar but below the maxi-
mum limit specified for the appliance. If this is
not the case, contact r’s Technical Assistance
Service or a professionally qualified technician.
If the boiler is not going to be used for an extended
period of time, contact r’s Technical Assistance
Service or a qualified technician to have the fol-
lowing minimum preparation carried out.
- Switch the appliance OFF at the control panel and
mains power switches
- Close the gas cock and heating water cock
- Drain the central heating circuit if there is any risk
of freezing.
The boiler must be serviced at least once a year.
This instruction manual is an integral part of the
boiler. It must be kept safe and must ALWAYS
accompany the boiler, even if it is sold to another
owner or transferred to another user or to another
installation.
If you damage or lose this manual, order a replace-
ment immediately from r’s Technical Assistance
Service.
Do not allow children or infirm persons to operate
this rTAU boiler unsupervised.
Do not operate any electrical devices or equip-
ment, including switches or domestic appliances,
etc., if you can smell gas or fumes. If you detect
any suspicious smells:
- Ventilate the room by opening all doors and win-
dows.
- Close the gas shut-off cock
- Report the fault immediately to r’s Technical
Assistance Service or a professionally qualified
technician.
Do not touch the boiler while barefoot or wet.
Never clean or service the boiler without first
disconnecting it from the mains electricity supply
by turning the main power switch and the control
panel switch OFF.
Do not tamper with or adjust the safety or control
devices without prior authorisation and instruc-
tions from the boiler’s manufacturer.
Never pull, disconnect, or twist the electrical
cables coming from the boiler even if it is discon-
nected from the mains electricity supply.
Do no obstruct or restrict the vents in the room
where the appliance is installed. Adequate venti-
lation is essential for correct combustion.
Do not expose the boiler to the elements. It is not
designed for outdoor use.
Do not switch the boiler off if outdoor temperature
drops below ZERO (risk of freezing)
Do not leave flammable substances in the room
where the boiler is installed, even inside proper
containers
Do not dispose of packaging material into the
environment, or leave it within the reach of chil-
dren, since it can become a potential hazard.
Dispose of packaging material in compliance
with applicable legislation.
The operation of any appliance that uses electrical power demands that a number of fundamental safety precautions
be respected. In particular:
GENERAL SAFETY INFORMATION
PRECAUTIONS

GENERAL
6
Le caldaie in acciaio r TAU steel boilers are triple flue
pass, condensing boilers for installation in a boiler room.
While they are designed primarily for central heating
purposes, in conjunction with a suitable storage cylinder
they can also be used to produce domestic hot water.
All parts that come into contact with the combustion
gases are made from titanium stabilised stainless steel
to ensure maximum resistance to the corrosive action of
acid condensation.
The boiler has been designed with the combustion cham-
ber at the top and the smooth pipe tube bundle at the
bottom to optimise heat exchange and energy efficiency
and to maximise the condensing effect.
The boiler has a high total water content which is diffe-
rentially distributed between its top and bottom sections.
This allows outgoing water to reach the set temperature
quickly while maintaining the condensing effect and the
water heating time around the tube bundle for as long as
possible.
TAU boilers feature lightly pressurised combustion cham-
bers for a smoother burner action, and high temperature
resistant, stainless steel turbulators inside the tube bun-
dle for maximum burner efficiency.
The boiler body is thoroughly insulated with a layer of
high density glass wool.
The paint finished external panelling is also internally
insulated with a layer of high density glass wool.
The boiler’s front door and the flue gas chamber can be
opened completely to facilitate the inspection, mainte-
nance and cleaning of internal parts and to speed up
servicing in general.
The front door can open in either direction and can be
opened without removing the burner. The door is factory
fitted with hinges on the left, but these can be reversed if
necessary to suit individual installations.
1
17
19
18
2
3
45 678(*)(*)
9
10
11
12
14
15
16
13
1 - Burner
2 - Flame inspection window with
pressure measurement point
3 - Door
4 - Panelling
5 - Outlet
6 - Safety device fitting
7 - Heating return (high temperature)
8 - Heating return (low temperature)
9 - Blind plug
10 - Instrument bulb/probe socket
11 - Combustion chamber
12 - Flue connection
13 - Flue gas box
14 - Inspection door
15 - Condensate drain
16 - Boiler drain
17 - Turbulators
18 - Flue pipes
19 - Second flue pass
PRODUCT DESCRIPTION
(*) On the TAU 1450 N, the low temperature heating return (8) is located at the rear of the boiler, and
the safety fitting (6) is flanged.

b When a TECH CLIMA TOP or CLIMA COMFORT control panel is installed, the boiler return (cold) line must be
equipped with a temperature sensor socket.
GENERAL 7
The rcontrol panels that can be used with rTAU steel boilers are listed below. These control panels cater for
all the needs of the heating system and of all the devices installed in it.
The burners recommended to obtain the best possible performance from rTAU boilers are:
( * ) Low Nox: low nitrogen oxide emissions.
NOTE: Burners must be fitted with a gas ramp device.
See the instruction manual provided with the burner
for further information on:
- burner installation
- electrical connections
- eurner adjustments.
CONTROL PANELS
RECOMMENDED BURNERS
BURNER TAU N-NC TAU N ACCESSORIES KIT
MODEL CODE 150 210 270 350 450 600 800 1000 1250 1450 BURNER PLATE LONG
HEAD
GAS
TWO STAGE
Gulliver BS 3D 3761716 (*) • 3001009
RS 34 t.c. 3789000
••
RS 44 t.c. 3789100 •
RS 50 t.c. 3784700 •
RS 70 t.c. 3785100 •
RS 100 t.c. 3785300 ••
RS 130 t.c. 3785500 •
RS 190 3785812 •
MODULATING
RS 34/M MZ t.c. 3788700 ••
RS 44/M MZ t.c. 3788800 •
RS 50/M t.c. 3781620 •
RS 70/M t.c. 3789600 •
RS 100/M t.c. 3789700 ••
RS 130/M t.c. 3789800 •
RS 190/M t.c. 3787620 •
Gulliver BS 3/M 3762300 (*) • 3002724
RS 25/M BLU 3910500 (*)
••
RS 35/M BLU 3910600 (*) •
RS 45/M BLU 3897304 (*) •
RS 68/M BLU 3897404 (*) •• 4031196
RS 120/M BLU 3897604 (*)
••
RS 160/M BLU 3788008 (*) ••
RS 25/E BLU 3910700 (*) ••
RS 35/E BLU 3910800 (*) •
RS 45/E BLU 3897330 (*) •
RS 68/E BLU 3897430 (*) ••
RS 120/E BLU 3897630 (*) •• 4031187
RS 160/E BLU 3788030 (*)
••
TECH CLIMA TOP for central
heating (1 direct zone and 2
mixed zones) and domestic hot
water production with a single
stage, two stage, or modulating
burner. Also for controlling solar
heating system and cascaded
boiler systems.
TECH CLIMA COMFORT for
central heating (1 direct zone
and 1 mixed zone) and dome-
stic hot water production with a
single stage burner. Also for con-
trolling solar heating system and
cascaded boiler systems.
TECH CLIMA MIX for controlling
1 additional mixed zone.

GENERAL
8
A
Ø
L
Do not re-use old burners if their nozzle lengths are below those specified in the table.
- Serial number plate
This is located on the boiler body and specifies the
serial number, model, and furnace power.
- Data plate
This lists the appliance’s technical specifications
and performance.
It comes inside the documentation envelope. On
completion of the installation you MUST APPLY IT in
a clearly visible position at the top of one of the side
panels.
If you damage or lose this label, order a replace-
ment immediately from r’s Technical Assistance
Service.
If these plates or any other means of clearly identifying the product are defaced, removed or lost, proper installa-
tion and servicing may be rendered difficult.
TAU boilers are identified by two plates:
IMPORTANT!
If you are installing a new boiler but re-using an old bur-
ner, always perform the following checks.
- Make sure that the performance of the old burner is
adequate for the requirements of the boiler.
- Make sure that the length and diameter of the burner
nozzle are as specified in the following table.
When you finish installing the burner in the boiler, fill
the gap between the burner nozzle and the refrac-
tory material in the door with the ceramic insulation
(A) supplied with the boiler.
PRODUCT IDENTIFICATION
MODEL 150
N-NC
210
N-NC
270
N-NC
350
N-NC
450
N-NC
600
N-NC 800 N 1000 N 1250 N 1450 N
Min. L (mm) 160 216 216 216 216 250 250 250 280 350
Ø (mm) 130 140 140 140 152 179 179 179 189 222

GENERAL 9
The stack must guarantee the minimum draught specified by applicable technical standards, assuming zero pres-
sure at the connection to the flue.
Values obtained with rburners: BS - RS - RS.../M - RS.../M BLU.
The following accessories are available, to be ordered separately:
ACCESSORIES
TECHNICAL SPECIFICATIONS
(*) Depends on return temperature (30-60°C)
(**) At Pn max and output T = 80°C, return T = 60°C and CO2= 9.7%
ACCESSORY CODE
Burner plate for steel boilers 4031187
Burner plate 4031196
N2 neutralisation kit (TAU 150-350) 4031810
HN2 neutralisation kit (TAU 150-350) 4031811
N3 neutralisation kit (TAU 450-1250) 4031812
HN3 neutralisation kit (TAU 450-1250) 4031813
Description BOILER model
150
N-NC
210
N-NC
270
N-NC
350
N-NC
450
N-NC
600
N-NC 800 N 1000 N 1250 N 1450 N
Fuel GAS
Rated heat input (Q max) 150,0 210,0 270,0 349,0 450,0 600,0 800,0 1000,0 1250,0 1450,0 kW
Rated heat input (Q min) 111,0 151,0 211,0 271,0 350,0 451,0 601,0 801,0 1001,0 1251 kW
Rated maximum useful heat output
(80/60°C) (Pn max) 147,8 207,3 269,9 346,7 445,2 593,6 791,2 989,4 1236,7 1434,6 kW
Rated minimum useful heat output
(80/60°C) (Pn min) 108,2 147,2 205,7 265,6 339,5 437,5 583,0 777,0 971,0 1213,5 kW
Rated maximum useful heat output
(40/30°C) (Pn max) 159,7 223,6 290,2 375,2 481,5 642,0 802,5 1070,0 1337,5 1551,5 kW
Useful efficiency at Pn max (80/60°C) 98,5 98,7 99,9 99,3 98,9 98,9 98,9 98,9 98,9 98,9 %
Useful efficiency at Pn min (80/60°C) 97,5 97,5 97,5 98,0 97,0 97,0 97,0 97,0 97,0 97,0 %
Useful efficiency at Pn max (50/30°C) 106,5 106,5 106,5 106,5 106,5 106,5 106,5 106,5 106,5 106,5 %
Useful efficiency at Pn max (40/30°C) 106,5 106,5 107,5 107,5 107,0 107,0 107,0 107,0 107,0 107,0 %
Useful efficiency at 30% of Pn (30°C) 106,6 106,8 109,0 107,3 107,0 107,0 107,0 107,0 107,0 107,0 %
Losses from stack for sensible heat
(Qmax) 1,7 1,7 1,5 1,5 1,9 1,9 1,9 1,9 1,9 1,9 %
Losses from casing with burner on 0,3 0,3 0,5 1,0 0,6 0,6 0,6 0,6 0,6 0,6 %
Constant pressure drop <1 %
Flue gas temperature (ΔT) < 45÷75 (*) °C
Flue gas mass flow rate (Q max) (**) 0,07 0,09 0,12 0,15 0,20 0,26 0,33 0,43 0,54 0,63 kg/sec
Furnace pressure 2,0 2,7 3,2 4,6 5,0 5,5 5,7 6,3 6,8 7,4 mbar
Furnace volume 172,0 172,0 241,0 279,0 442,0 496,0 753,0 845,0 1037,0 1249,0 dm3
Total volume of flue gas side 253,0 277,0 413,0 482,0 737,0 860,0 1290,0 1454,0 1763,0 2097,0 dm3
Heat exchanger surface area 6,1 8,8 13,0 16,3 21,8 28,8 39,6 46,5 56,2 62,28 m2
Volumetric heat load (Q max) 872,1 1220,9 1120,3 1250,9 1018,1 1209,7 996,0 1183,4 1205,4 1160,9 kW/m3
Specific heat load 23,75 23,10 20,4 20,9 20,1 20,3 18,5 21,0 21,7 22,6 kW/m2
Maximum condensate production 18,4 27,4 31,9 40,9 52,2 73,8 88,0 111,4 132,7 159,5 l/h
Maximum working pressure 6 bar
Maximum admissible temperature 100,0 °C
Maximum working temperature 80,0 °C
Pressure drop ΔT 10°C 150,1 100,4 121,5 128,7 30,2 33,8 46,4 54,0 36,0 43,2 mbar
Pressure drop ΔT 20°C 36,3 28,4 30,6 28,7 8,5 9,0 13,4 16,3 10,2 11,3 mbar
Water capacity 323 360 495 555 743 770 1320 1395 1825 1900 l
Turbulators 22 39 52 59 72 90 106 114 130 145 n°

Have r’s Technical Assistance Service start-up your
rTAU boiler for the first time. Once this has been
done, the boiler can be left to function automatically.
Under certain circumstances, such as after long periods
of disuse, the service engineer responsible for the boiler
may need to re-start it without involving the Technical
Assistance Service.
To do so, perform the following checks and operations:
- Check that the gas cock and heating water cock are
shut.
- While the system is still cold, check that working pres-
sure in the heating circuit is over 1 bar but below the
maximum limit specified for the appliance.
-
Since the control panel incorporates a temperature control
function, make sure that the control panel is switched on.
- Adjust the timer thermostat (if installed) or the temperatu-
re control to the desired temperature (~20° C).
- Turn the system’s main power switch ON.
- Turn the control panel power switch ON and make sure
that the green power indicator lights.
- Make the settings as instructed in the instruction
manual for your control panel.
SYSTEM MANAGER
10
INITIAL START-UP
10
ON
OFF

The burner should now ignite and remain in operation
until the set temperature is reached.
The burner will then switch off and on automatically to
maintain the set temperature without further operator
action.
If any ignition faults or malfunctions occur, the burner
performs a “LOCKOUT SHUTDOWN”. This is shown by
the red button light on the burner and by the warning
light on the control panel.
If a “LOCKOUT SHUTDOWN” occurs, wait about 30
seconds before resetting the burner.
To reset the burner, press the red button light on the
burner and wait until the flame ignites.
Repeat this operation 2 -3 times at the most. If the pro-
blem persists after that, call r’s Technical Assistance
Service.
If the boiler is not going to be used for an extended
period of time, perform the following operations:
- Turn the control panel power switch OFF and make
sure that the green power indicator goes out.
- Turn the system’s main power switch OFF.
- Close the fuel cock and heating water cock.
- Drain the central heating circuit if there is any risk of
freezing.
Contact r’s Technical Assistance Service if you
encounter any problems in completing the above
procedure.
11
SYSTEM MANAGER
PREPARING FOR EXTENDED PERIODS OF DISUSE
11
ON
OFF

Use a cloth damped in soapy water to clean the boiler’s
external panelling.
To remove stubborn marks, use a cloth damped in a 50%
mix of water and denatured alcohol or a suitable cleaning
product.
Carefully dry the boiler after cleaning.
Do not use abrasive cleaning pads or powder deter-
gents.
Never clean the boiler without first disconnecting it
from the mains electricity supply by turning the main
power switch and the control panel switch OFF.
The combustion chamber and flues must be cle-
aned periodically by r’s Technical Assistance
Service or by a qualified technician (see page 35).
THE PERSON RESPONSIBLE FOR SYSTEM OPERATION
MUST ENSURE THAT PROFESSIONALLY QUALIFIED
PERSONNEL UNDERTAKE PERIODIC MAINTENANCE
AND COMBUSTION EFFICIENCY MEASUREMENTS. (In
Italy this is stipulated by Presidential Decree 412 of the
26th August 1993.)
r’s Technical Assistance Service is qualified to satisfy
these legal requirements and can also provide useful
information on MAINTENANCE PROGRAMMES desig-
ned to guarantee:
- greater safety;
- compliance with applicable legislation;
- freedom from the risk of fines in the event of spot
checks.
12
CLEANING
MAINTENANCE
SYSTEM MANAGER

Seller: .............................................................................................................................................
Mr. .......................................................................................................................................................
Address .......................................................................................................................................
Tel. ......................................................................................................................................................
Technical Assistance Service: ....................................................................
Mr. .......................................................................................................................................................
Address .......................................................................................................................................
Tel. ......................................................................................................................................................
Installer:........................................................................................................................................
Mr. .......................................................................................................................................................
Address ......................................................................................................................................
Tel. .....................................................................................................................................................
Date Work done
13
USEFUL INFORMATION
SYSTEM MANAGER

INSTALLER
14
rTAU steel boilers come in 2 separate crates:
1) BOILER BODY CRATE, bearing the documentation
envelope (A) and containing:
- Instruction manual;
- Data label (to be applied to the panelling on com-
pletion of the installation);
- Certificate of Warranty and water test certificate;
- Bar code labels.
- Spare parts catalogue
- Ceramic insulation (B)
- Cleaning brush (C).
The instruction manual is an integral part of the
boiler. Once located, read it thoroughly and keep
it safe.
2) PANELLING CRATE, complete with assembly acces-
sories, protected by cardboard packaging and a
wooden crate.
IMPORTANT!
For the boiler to function correctly, it must be connected
to a rcontrol panel and dedicated control accesso-
ries.
UNPACKING THE PRODUCT
A
C
B

INSTALLER 15
rTAU steel boilers are fitted with lifting attachments.
Take great care when moving them and only use lifting
equipment of adequate capacity.
Remove the transport straps and remove the wooden
pallet before positioning the boiler.
Wear suitable personal protective equipment and
use suitable safety devices.
OVERALL DIMENSIONS AND WEIGHTS
HANDLING
DESCRIPTION BOILER model
150
N-NC
210
N-NC
270
N-NC
350
N-NC
450
N-NC
600
N-NC 800 N 1000 N 1250 N 1450 N
A - Base width 640 640 750 750 790 790 950 950 1070 1130 mm
B - Overall width 740 740 850 850 900 900 1060 1060 1180 1225 mm
L - Depth 1455 1455 1630 1830 2035 2235 2560 2810 3010 3080 mm
L1 - Base depth 1295 1295 1470 1670 1875 2075 2400 2650 2850 2850 mm
H - Height of water fittings 1315 1315 1450 1450 1630 1630 1910 1910 2030 2180 mm
H1 - Boiler height 1300 1300 1437 1437 1615 1615 1900 1900 2015 2167 mm
D - Height of burner plate 925 925 1030 1030 1235 1235 1390 1390 1495 1590 mm
Weight of boiler 510 530 677 753 1095 1250 1870 2085 2515 3050 Kg
Weight of panelling 50 50 60 70 90 120 140 160 215 230 Kg
AL1 40 120
L
D
H1
H
150
B 161

INSTALLER
16
rTAU steel boilers must be installed in a dedicated
boiler room, with adequately sized vents, in compliance
with applicable laws and standards.
If at all possible, the boiler should be installed on a raised
base to stop the burner fan sucking up dust and to facili-
tate installation of a condensate drain system.
The boiler condensate drain must be located above the
height of the lid of the system’s condensate neutraliser.
The gas supply pipe must be installed in such away that
the boiler’s panelling can be removed and the front door
opened without having to remove the burner.
When installing the boiler, allow sufficient space
around it to access all safety and control devices
and to permit easy maintenance.
If the specific weight of the gas supply to the bur-
ner is greater than the specific weight of air, install
all electrical parts at least 500 mm above floor
level.
Do not install the boiler outdoors. It is not designed
to work outdoors and is not fitted with the necessa-
ry automatic anti-frost systems to do so.
PLACE OF INSTALLATION
≥1 m
≥1 m≥1 m
L
≥L
H
B
~ 0,1 m
DESCRIPTION BOILER model
150
N-NC
210
N-NC
270
N-NC
350
N-NC
450
N-NC
600
N-NC 800 N 1000 N 1250 N 1450 N
B - Width 750 750 850 850 900 900 1000 1000 1200 1250 mm
L - Depth 1350 1350 1620 1820 1930 2140 2400 2700 2920 3100 mm
H - Overall height
(boiler + base) 1420 1420 1540 1540 1700 1700 2010 2010 2130 2280 mm

INSTALLER 17
HEATING CIRCUIT WATER
INTRODUCTION
The water used in the central heating system MUST be
suitably treated to ensure the correct functioning of the
system and to guarantee an extended working life for the
boiler and all other system components.
Sludge, limescale and other contaminants in the water
supply can cause irreversible damage to the boiler even
in relatively short times, and despite the use of top quality
materials in its manufacture.
It is common practice for water treatment to be applied
only to old systems and systems already affected by li-
mescale, deposits and sludge. In stark contrast with this
practice, proper water treatment is actually essential to
extend component life and to ensure the continued effi-
ciency of new installations too.
For further technical information on water treatment, refer
to the following section which contains a study published
by ANICA (the Italian National Association of Steel Boi-
ler Manufacturers), and to the appendix to this manual,
which contains an extract from UNI standard 8065 gover-
ning ‘Water Treatment in Domestic Heating Systems’.
Contact r’s Technical Assistance Service for further
information on water additives and their use.
If it proves impossible to treat the heating system
water supply properly because the water charging
system is automatic and uncontrolled, if there are no
barriers installed to prevent water oxygenation, and
if the heating circuit includes an open expansion
vessel, then the boiler itself must be separated from
the heating system by means of a heat exchanger.
Heating system water: Instructions for the
design, installation and management of he-
ating systems
1. Chemical and physical characteristics
Reference standards prescribe certain required values.
(In Italy the relevant standard is UNI-CTI 8065 ‘Water
Treatment in Domestic Heating Systems’, June 1989 edi-
tion.)
In particular, this standard assumes that the chemical and
physical composition of heating system water is similar to
that of drinking water.
The standard also requires that all systems be fitted with
a chemical water treatment device to protect system com-
ponents as well as an inlet filter to prevent solid particles
from entering the system in suspension and causing cor-
rosion or sludge.
Layout showing the water treatment devices required
by Italian standard UNI-CTI 8065, according to the sy-
stem’s overall heat output
A
Water treatment for heating installations:
- with heat output < 350 kW and water supply hardness <
35° fr
- with heat output > 350 kW and water supply hardness <
15° fr
- a filter is recommended for systems with heat output < 350
kW
- a filter is obligatory for systems with heat output > 350 kW
B
Water treatment for heating installations:
- with heat output < 350 kW and water supply hardness
> 35° fr
- with heat output > 350 kW and water supply hardness
> 15° fr
- a filter is recommended for systems with heat output <
350 kW
- a filter is obligatory for systems with heat output > 350
kW
Chemical and physical water parameters required by
Italian standard UNI-CT 8065
*The maximum limit of pH 8 refers to systems with radia-
tors made from aluminium or light alloy elements.
**Higher pH values are indicative of corrosion.
Parameters Unit of
measure
System
filling water
Circuit
water
pH* - 7÷8
Total
hardness
(CaCO3)
°fr <15 -
Iron (Fe)** mg/kg - <0,5
Copper
(Cu)** mg/kg - <0,1
Appearance Clear Clear if
possible
Y
AB
Filter Filter
Water
softener
Chemical
treatment
unit
Boiler Boiler
Chemical
treatment
unit

Identification of water treatments required by Italian
standard UNI CTI 8065
A resin ion exchange type water softener is required. The
filter may be either washable or disposable.
The most suitable form of water treatment consists of the
addition of specific chemical products (water conditio-
ners) to:
- Stabilise hardness
- Disperse unwanted organic and inorganic deposits
- De-oxygenate the water and passivate component sur-
faces
- Correct the pH
- Form a protective film over component surfaces
- Control biological growth
- Provide anti-freeze protection
Chemical products used for water treatment must
be compatible with applicable water pollution laws.
Provided it is properly applied, Italian standard
UNI-CTI 8065 guarantees the safe functioning of a
heating system. The desired effects of the standard
may nevertheless be cancelled out by incorrect in-
stallation or system management practices, inclu-
ding excessive topping up and the circulation of
water through open expansion vessels.
The standard is often not properly respected. In
particular, in existing systems, insufficient attention
is paid to the characteristics of the water supply
and to the need to adopt corrective measures.
2. Central heating systems
Possible causes for corrosion and limescale
Until some forty years ago, central heating was not in
common use in the home, and heating was provided in-
stead by systems that today are considered extremely
old-fashioned. The problem of water characteristics was
not therefore of any real importance.
Then the energy crisis, the widespread appearance of
central heating and the introduction of standards gover-
ning it stimulated boiler and heating system manufactu-
rers to develop more sophisticated materials and more
advanced (though often more delicate) high efficiency
heating solutions. Unfortunately because they failed to
appreciate the importance of water treatment, the excel-
lent efficiency levels initially achieved were rapidly lost to
limescale and corrosion.
Typical problems encountered in central heating systems
include:
- the breakage of heated surfaces through overheating
caused by the thermal insulation of limescale deposits
on the water side
- oxygen corrosion
- deposit corrosion
- stray current corrosion (now rare)
- diffused and localised acid corrosion (caused by the
aggressive nature of water with a pH < 7)
2.1 Limescale deposits
Limescale forms when the calcium and magnesium bicar-
bonates that are dissolved in the water at ambient tempe-
rature become chemically transformed when the water is
heated.
Calcium bicarbonate forms calcium carbonate, water and
carbon dioxide, while magnesium bicarbonate transforms
into magnesium hydroxide and carbon dioxide.
Calcium bicarbonate Ca (HCO3)2
----increased temperature---->
CaCO3+ H2O + CO2
Magnesium bicarbonate Mg (HCO3)2
----increased temperature---->
Mg(OH)2+ 2CO2
Calcium carbonate and magnesium hydroxide precipitate
to form insoluble deposits that adhere and compact on
surfaces to form limescale, a substance with an extremely
high thermal insulating power. The coefficient of heat ex-
change of a 3 mm layer of limescale is the same as that of
a steel sheet 250 mm thick! It has been calculated that 2
mm of limescale throughout a system causes an increase
in consumption of 25%! The reactions that cause limesca-
le to form accelerate as temperature increases. Generally
speaking, if water comes from an area rich in calcium and
magnesium deposits, it will be ‘hard’ water and perfect-
ly capable of forming limescale at any temperature abo-
ve 40°C. Inside a boiler, limescale forms mainly in areas
subject to direct heat and high temperatures. That is why
it is so common to find deposits localised in a few specific
areas, where temperature is the highest.
A coating of limescale of only 1 mm can effectively reduce
the cooling of the surface it covers.
If that coating continues to increase, it can cause seve-
re overheating in metal parts and consequent breakage
through thermal stress. The water used to fill a heating
system for the first time never contains enough calcium
and magnesium bicarbonates to endanger the boiler. It is
continuous topping up that causes thick deposits to form,
leading to boiler breakdown.
2.2 Oxygen corrosion
Oxygen corrosion is the result of a natural phenomenon,
the oxidation of steel. In nature, iron does not occur in its
pure state, but always in combination with other elements
and nearly always with oxygen (as ferrous or ferric oxide).
Iron can only be separated from its oxygen bond in a blast
furnace capable of smelting the ore.
Once solidified in the form of steel (and therefore combi-
ned with other elements), iron inevitably tends to re-ab-
sorb oxygen from the surrounding air or water in order to
re-establish its original equilibrium. This is the explanation
behind the normal process of oxidation.
The steel sheets and tubes inside a boiler or heating sy-
stem absorb oxygen not from the water (H2O), but from
micro-bubbles of air naturally dissipated in it.
INSTALLER
18

Remember that air dissolved in water has an oxygen con-
tent of around 35%, far higher than air in its natural ga-
seous state.
It is therefore particularly easy for steel that comes into
contact with water in heating systems to absorb oxygen
from the micro-bubbles contained in it to form the charac-
teristically red coloured ferric oxide Fe2O3(rust).
4Fe + 3O2= 2Fe2O3(ferric oxide, or rust)
If not prevented, oxidation inevitably leads to a reduction
on the original thickness of the metal, and eventually to its
complete penetration.
Corrosion is easily recognisable from the formation of
small round pock-marks (like tiny craters) in the surface of
the metal. If corrosion ever penetrates all the way through
a boiler part, massive leakage is inevitable.
Oxygen corrosion affects metal throughout the heating
system and not just at determined points. It is therefore
a particularly destructive form of corrosion. Furthermore,
because it cannot be repaired, it can easily cause perma-
nent leakage from the circuit.
If, on the other hand, the system is well protected from
the outside world and top-ups of fresh water are not conti-
nuously added, the oxygen content in the circuit gradually
diminishes. The little oxidation that does occur occurs in a
reduced oxygen environment, and forms black magneti-
te (Fe3O4) which actually protects steel surfaces against
further attack.
3Fe + 2O2= Fe3O4(triiron tetraoxide, or magnetite)
2.3 Deposit corrosion
Deposit corrosion is an electro-chemical phenomenon
caused by the presence of foreign bodies (sand, rust,
etc.) in the water mass. These solid substances generally
form deposits (sludge) in the bottom of the boiler.
The lower parts of the boiler can therefore be affected
by a chemical reaction of micro-corrosion caused by the
electrochemical potential difference created between the
metal (steel) and the impurities around it.
2.4 Stray current corrosion
Stray current corrosion is actually very rare today, but can
be caused by the different electrical potentials of the boi-
ler water and the metal body of the boiler or piping crea-
ting a cathode/anode effect.
All metal part of the boiler should therefore be connec-
ted to an efficient ground (earth) point, even though this
form of corrosion is actually caused by the passage of DC
current, no longer used for domestic power. Stay current
corrosion is easily identified by the regular tiny conical
holes it leaves.
2.5 Diffused and localised acid corrosion
Other forms of corrosion exist that are harder to see but
nonetheless dangerous because they affect the entire he-
ating system and not just the boiler.
These forms of corrosion are generally due to the water
becoming acidic (pH < 7), and are caused by:
- Incorrect water softening and the presence of carbon
dioxide (which lowers the water’s pH). Carbon dioxide
is released more easily in softened water and also forms
during the limescale formation process. Acid corrosion
is diffuse and attacks the entire circuit more or less uni-
formly.
- Incorrect acid washing (e.g. washing done without a
passivating agent). Acid introduced into the circuit can
cause localised perforation if it is not properly removed
from all parts of the system. The formation of corrosion
can easily be detected by analysing the chemical com-
position of the water. Even a minimal iron content is a
clear sign that corrosion is occurring.
The technical details provided in this section refer
specifically to domestic and industrial hot water he-
ating systems with working temperatures up to 100
°C.
Users of this type of heating system (unlike users of
steam and super-heated water systems) frequently
underestimate the potential problems caused by
failure to perform proper water treatment and by sy-
stem design and operating errors.
Unfortunately, failure to cater for the risks involved
often leads to serious damage to the boiler and to
the entire circuit.
In Italy, Article 7 of Law 46/90 governing the treat-
ment of potable water, states that central heating sy-
stems and domestic hot water production systems
must be constructed according to Italian UNI and
CEI standards (UNI 8065). Depending on the condi-
tions of the water supply, suitable treatment systems
must be built in from the design stage to ensure that
the water used meets the relevant requirements.
The system operator must likewise maintain the sy-
stem within the specified operating limits, using all
necessary checks and actions to do so.
19
INSTALLER

3. New central heating systems
Mistakes to avoid and precautions
From what has been said above we can see that it is es-
sential to avoid two main factors that could lead to corro-
sion. These are contact between the water in the system
and the air and the continuous addition of fresh water to
the circuit.
To eliminate contact between system water and the air
(thus avoiding oxygenation of the system water), we need
to:
- ensure that the expansion vessel is a closed vessel, and
of the correct size and pre-charge pressure (the pressu-
re to be checked periodically);
- ensure that the system is always kept at a pressure hi-
gher than atmospheric pressure at all points (including
the pump suction side) and at all operating conditions
(precisely because the seals, gaskets and joints in a
water circuit are designed to resist pressure from within,
but not to resist a vacuum within);
- ensure that no part of the system is made from materials
that are permeable to gases (e.g. plastic pipes with no
oxygen barrier used in floor heating systems).
The original system filling water and any topping
up water must always be filtered (using synthetic or
metal mesh filters with a filtration rating of no less
than 50 microns) to prevent sludge from forming
and triggering deposit induced corrosion.
Loss of water from the system, and the consequent
need to add water, can be caused not only by leaks
from the circuit, but also from the incorrect sizing
of the expansion vessel and by an incorrect initial
precharge pressure. (If normal thermal expansion
causes pressure in the system to increase beyond
the setting of the safety valve, that safety valve will
keep opening continuously.)
In theory, once filled and bled of all air, a heating circuit
should not need any further topping up.
If it does, one of the problems listed above is inevita-
bly occurring. Any top-ups need to be monitored (by a
counter), treated and recorded in the heating system’s
technical log. It is simply not enough to rely on the reas-
suring presence of a water softener in conjunction with an
automatic filling system.
The continuous addition to a system of water softened to
15°fr will quickly cause deposits/limescale to form on the
boiler parts, especially at the hottest points.
Systems should also be heated up slowly the first time
they are switched on, then taken to maximum working
temperature to facilitate de-aeration (since gas will not be
released from the water at low temperatures).
If more than one boiler is installed in a large system, all
boilers must be switched on at the same time to ensure
that the initial small precipitation of limescale is uniformly
distributed.
4. Reconditioning old heating systems
Frequent mistakes and necessary precautions
Frequently, when old central heating systems are recondi-
tioned, especially when old boilers are replaced, it is im-
possible to make any modifications to the existing circuit.
Nevertheless, failure to pay any attention to the problems
involved can cause rapid damage to the new boiler.
Over years of functioning, a protective black coating may
well have built up inside an old circuit. This coating (for-
med mainly from magnetite, Fe3O4, which forms when
iron oxidises in an oxygen starved environment) actually
offers effective protection against further corrosion.
If new parts with clean metal surfaces, especially boilers,
are fitted in an old system, they inevitably become the
sacrificial anode for the entire heating circuit. If leaks from
a system cannot be repaired and topping up is therefore
inevitable, great care must be taken in finding a solution
to the problem, and particularly in choosing the water tre-
atment system to use. Water treatment systems should
be similar to those used in steam heating systems to ful-
ly decalcify the incoming water (hardness <0.5°fr) while
maintaining a non-aggressive pH.
Film-forming de-oxidising agents will also have to be do-
sed in, and a physical filtration system fitted to prevent
any impurities entering the circuit.
The reconditioned system must then be started up as in-
structed above.
The following notes deal with a number of important is-
sues, and can be of help in reconditioning old systems
and in guaranteeing the correct functioning of new boilers
over time.
- If an old heating system has an open expansion vessel,
this should be converted to a closed vessel if at all pos-
sible. Today, this conversion can be performed without
unduly affecting the working pressure in the system.
This modification solves many of the problems caused
by contact between system water and the air (corrosion
etc.) and avoids having to condition the water with de-
oxidising products, which would otherwise have to be
added at regular intervals in an open vessel system.
- f an old system has a very large circuit or is a radiant
panel system with plastic pipes with no oxygen barrier,
the boiler water circuit should be separated from the he-
ating circuit water by installing a heat exchanger made
from corrosion resistant material. This enables the new
boiler to remain protected even in old systems that can-
not be modernised.
INSTALLER
20