Ariston ACO 35 MFFI User guide

Country of destination: GB/IE
Installation and
Servicing
Instructions
Type C Boilers
ACO 35 MFFIG.C.N: 47-116-35
LEAVE THESE INSTRUCTIONS
WITH THE END USER
SERIES

2
TABLE OF CONTENTS
1. GENERAL INFORMATION
1.1. GENERAL INFORMATION 3
1.2. TECHNICAL INFORMATION 4
1.3. OVERALL VIEW 6
2. INSTALLATION
2.1. REFERENCE STANDARDS 7
2.2. SITING THE APPLIANCE 7
2.3. OVERALL DIMENSIONS 8
2.4. MINIMUM CLEARANCES 8
2.5. MOUNTING THE APPLIANCE 9
2.6. ELECTRICAL CONNECTION 9
2.7. GAS CONNECTION 9
2.8. WATER CONNECTIONS 10
2.9. FLUE CONNECTIONS 13
2.9.1 FITTING THE COAXIAL FLUE
(Ø 60 / 100 HORIZONTAL)14
2.9.2 FITTING THE 5” FLUE
(Ø 80 / 125 Horizontal/Vertical) 15
2.9.3 FITTING THE COAXIAL FLUE
(Ø 60 / 100 VERTICAL) 16
2.9.4 FITTING THE TWIN PIPE (Ø80 / 80) 17
2.10. FITTING THE MECHANICAL/DIGITAL
TIME CLOCK 20
2.11. SETTING THE MECHANICAL TIME CLOCK 22
2.11.1. SETTING THE DIGITAL TIME CLOCK 22
2.12. ACCESSORY CONNECTION 24
2.13. ELECTRICAL DIAGRAM 26
2.14. WATER CIRCUIT DIAGRAM 28
3. COMMISSIONING
3.1. INITIAL PREPARATION 30
3.2. REMOVING THE CASING 32
3.3. CONTROL PANEL 33
3.4. INITIAL START-UP 35
3.5. DISPLAY: MESSAGES SHOWN DURING
NORMAL OPERATION 36
3.6. OPERATING PARAMETERS 37
3.6.1. REGULATION MENU TABLE 37
3.6.2. SETTINGS DISPLAY 43
3.6.3. GAS REGULATION CHECK 44
3.6.4. IGNITION DELAY ADJUSTMENT 45
3.6.5. ADJUSTING THE MAXIMUM HEATING
POWER 45
3.6.6. SOFT LIGHT ADJUSTMENT 45
3.7. CHANGING THE TYPE OF GAS 45
3.8. ADJUSTING THE DOMESTIC HOT
WATER FLOW RATE 45
3.9. BALANCING THE CENTRAL
HEATING SYSTEM 45
3.10. BOILER SAFETY SYSTEMS 46
3.11. COMPLETION 47
3.12. DRAINING 47
4. ZONE VALVES 48
5. SEQUENCE OF OPERATION 51
5.1 CENTRAL HEATING MODE 51
5.2 DOMESTIC HOT WATER MODE 51
6. MAINTENANCE 52
6.1. GENERAL REMARKS 52
6.2. CLEANING THE PRIMARY EXCHANGER 52
6.3. CLEANING THE CONDENSATE TRAP 52
6.4. OPERATIONAL TEST 52
7. SERVICING INSTRUCTIONS 53
7.1. REPLACEMENT OF PARTS 53
7.2. TOGAIN GENERAL ACCESS 53
7.3. ACCESS TO THE COMBUSTION
CHAMBER 54
7.3.1. REMOVING THE FAN 54
7.3.2. REMOVING THE AIR PRESSURE SWITCH 55
7.3.3. REMOVING THE BURNER 55
7.3.4. REMOVING THE ELECTRODES 56
7.3.5. REMOVING THE HEAT EXCHANGER 56
7.3.6. REMOVING THE CONDENSATE
TRAP (TUBE)58
7.3.7. REMOVING THE CONDENSATE TRAP 58
7.4. ACCESS TO THE GAS VALVE 59
7.4.1. REMOVING THE GAS VALVE 59
7.4.2. REMOVING THE SPARK GENERATOR 60
7.5. ACCESS TO THE WATER CIRCUIT 60
7.5.1. REMOVING THE D.H.W.
(SECONDARY) EXCHANGER 60
7.5.2. REMOVING THE SAFETY VALVE 61
7.5.3. REMOVING THE AUTOMATIC AIR VENT 61
7.5.4. REMOVING THE DIVERTER VALVE
ACTUATOR 62
7.5.5. REMOVING THE DHW FLOW SWITCH
(MFFI ONLY)62
7.5.6. REMOVING THE PUMP 62
7.5.7. REMOVING THE PRESSURE GAUGE 63
7.5.8. REMOVING THE EXPANSION VESSEL 64
7.5.9. REMOVING THE D.H.W. TEMPERATURE
PROBE (N.T.C. - MFFI ONLY)64
7.5.10. REMOVING THE C.H. FLOW
TEMPERATURE PROBE (N.T.C.) 65
7.5.11. REMOVING THE C.H. RETURN
TEMPERATURE PROBE (N.T.C.) 65
7.6. ACCESS TO THE CONTROL SYSTEM 66
7.6.1. CHECKING THE FUSES 66
7.6.2. REMOVING THE PRINTED CIRCUIT
BOARDS 66
7.6.3. REMOVING THE TIME CLOCK 67
8. FAULT FINDING 68
8.1 FAULT FINDING GUIDE
(FLOW-CHARTS)68
9. SHORT SPARES PARTS LIST 72
10. ANNUAL MAINTENANCE CHECKLIST 76
11. BENCHMARK COMMISSIONING
CHECKLIST 78
12. SERVICE INTERVAL RECORD 79
PAGE PAGE

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This manual is an integral and essential part of the product. It
should be kept with the appliance so that it can be consulted by
the user and our authorised personnel.
Please carefully read the instructions and notices about the unit
contained in this manual, as they provide important information
regarding the safe installation, use and maintenance of the
product.
For operating instructions please consult the separate Users
Manual.
1. GENERAL INFORMATION
Read the instructions and recommendations in these Installation
and Servicing Instructions carefully to ensure proper installation,
use and maintenance of the appliance.
Keep this manual in a safe place. You may need it for your own
reference while Servicing Technicians or your installer may
need to consult it in the future.
The ACO 35 MFFI is a combined appliance for the production of
central heating (C.H.) and domestic hot water (D.H.W.) and is
designed for domestic use only..
This appliance must be used only for the purpose for which it is
designed.
The manufacturer declines all liability for damage caused by
improper or negligent use.
No asbestos or other hazardous materials have been used in
the fabrication of this product.
MTS recommends the use of protective clothing when installing
and working on the appliance i.e. gloves.
Before connecting the appliance, check that the information
shown on the data plate and the table in Section 1.2 (page 4)
comply with the electric, water and gas mains of the property.
You will find the data plate on the inside of the casing.
The gas with which this appliance operates is also shown on the
label at the bottom of the boiler.
Do not install this appliance in a damp environment or close to
equipment which spray water or other liquids.
Do not place objects on the appliance.
Do not allow children or inexperienced persons to use the
appliance without supervision.
If you smell gas in the room, do not turn on or off light
switches, use the telephone or any other object which might
cause sparks.
Open doors and windows immediately to ventilate the room.
Shut the gas mains tap (at or adjacent to the gas meter) or the
valve of the gas cylinder and call your Gas Supplier immediately.
Always disconnect the appliance either by unplugging it from
the mains or turning off the mains switch before cleaning the
appliance or carrying out maintenance.
In the case of faults or failure, switch off the appliance and
turn off the gas tap. Do not tamper with the appliance.
For repairs, call your local Authorised Servicing Agent and
request the use of original spare parts. For in-guarantee repairs
contact MTS (GB) Limited.
1.1. GENERAL INFORMATION

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Name
CE Certification
Flue Type
Heat Input max (Domestic Hot Water) kW
Heat Input max/min (Central Heating) kW
Heat Output max/min (Central Heating) kW
Heat Output max/min (Domestic Hot Water) kW
Efficiency of Nominal Heat Input (60/80°C) %
Efficiency of Nominal Heat Input (30/50°C) %
Efficiency at 30% of Nominal Heat Input (47°C) %
Efficiency at 30% of Nominal Heat Input (30°C) %
Efficiency at Minimum Input %
Efficiency (Dir. 92/42/EEC)**
SEDBUK Rating Band / %
Heat Loss to the Casing (∆T=50°C) %
Flue Heat Loss with Burner Operating %
General Info
Energy Performance
Max Discharge of Products of Combustion (G20) Kg/h
Temp. of exhaust fumes at nominal capacity °C
CO2Content %
O2Content %
CO Content ppm
Nox Class
Emissions
Head Loss on Water Side (max) (∆T=20°C) mbar
Residual Head of System bar
Expansion Vessel Pre-load Pressure bar
Maximum Heating Pressure bar
Expansion Vessel Capacity l
Maximum Water Content of System l
Heating Temperature max/min (High temperature) °C
Heating Temperature max/min (Low Temperature) °C
Central Heating
Domestic Hot Water Temperature (approx) max/min °C
Specific Flow Rate (10 minutes/∆T 30°C) l/min
D.H.W. Flow Rate ∆T=25°C l/min
D.H.W. Flow Rate ∆T=35°C l/min
D.H.W. Minimum Flow Rate l/min
Pressure of Domestic Hot Water max/min bar
Domestic Hot Water
Nominal Pressure Natural Gas (G20) mbar
Consumption at Nominal Capacity(G20) m3/h
Gas Consumption after 10 Minutes* m3
Gas
Electrical Supply V/Hz
Power Consumption W
Minimum Ambient Temperature °C
Protection Grade of Electrical System IP
Internal Fuse Rating
Electrical Data
Weight Kg
Casing Dimensions (D/W/H) mm
G.C. Number
ACO 35 MFFI
1312BQ4461
C13-C33-C43-C53-C83-B23-B33
44.6
62
9.4
3.8
109
5 (70 mg/kW/h)
200
0.2
0.7
3
7
130
82 / 46
75 / 25
56 / 36
16
18.84
13.5
2.5
6 / 0.2
20
3.17
0.37
3
4
230/50
145
+5
24D
2A Fast Fuse
43
310/450/750
47-116-35
* Calculated at 70% maximum output
** Calculated on Upper calorific value
Max. Condensate produced l/h
PH of condensate PH
1.2. TECHNICAL INFORMATION
37.2
33.3 / 7.4
29.4 / 6.5
33.3 / 7.4
88.2
94.6
92.5
97.4
87.3
A / 90.2
0.4
1.7

1
2
3
4
5 6
11
7
8
9
10
11 1312 14 15 16
17
18
19
20
21
22
23
24
25
26
5
LEGEND:
1. Air Release Valve
2. Main Heat Exchanger (Stainless Steel)
3. Detection Electrode
4. Central Heating Flow Temperature Probe
5. Overheat Thermostat
6. Central Heating Return Temperature Probe
7. Air / Gas Mixer
8. Gas Valve
9. P.C.B. Box
10. Diverter Valve
11. Condensate Discharge
12. Condensate Trap
13. Low Water Pressure Switch
14. Domestic Hot Water Temperature Probe
1.3. OVERALL VIEW
FIG. 1.0
15. Secondary Heat Exchanger
16. Domestic Hot Water Flow Switch
17. Circulation Pump with Automatic Air Release Valve
18. Safety Valve (3 bar)
19. Automatic By-pass
20. Fan
21. Ignition Electrode
22. Silencer
23. Spark Generator
24. Expansion Vessel
25. Combustion Analysis Test Point
26. Flue Connector

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The technical information and instructions provided herein below
are intended for the installer / Servicing Technician so that the
unit may be installed and serviced correctly and safely.
In the United Kingdom the installation and initial start up of the
boiler must be by a CORGI Registered Installer in accordance
with the installation standards currently in effect, as well as with
any and all local health and safety standards i.e. CORGI.
In the Republic of Ireland the installation and initial start up of
the appliance must be carried out by a Competent Person in
accordance with the current edition of I.S.813 “Domestic Gas
Installations”, the current Building Regulations, reference should
also be made to the current ETCI rules for electrical installation.
This appliance must be installed by a competent installer in
accordance with current Gas Safety (installation & use)
Regulations.
The installation of this appliance must be in accordance with the
relevant requirements of the Local Building Regulations, the
current I.E.E. Wiring Regulations, the byelaws of the local water
authority, in Scotland, in accordance with the Building Standards
(Scotland) Regulation and Health and Safety document No. 635
“Electricity at work regulations 1989” and in the Republic of
Ireland with the current edition of I.S. 813, the Local Building
Regulations (IE).
C.O.S.H.H.
Materials used in the manufacture of this appliance are non-
hazardous and no special precautions are required when
servicing.
Installation should also comply with the following British
Standard Codes of Practice:
and in the Republic of Ireland in accordance with the following
Codes of Practice:
2. INSTALLATION
2.1. REFERENCE STANDARDS
BS 7593:1992 Treatment of water in domestic hot water
central heating systems
BS 5546:1990 Installation of hot water supplies for
domestic purposes
BS 5440-1:2000 Flues
BS 5440-2:2000 Air supply
BS 5449:1990 Forced circulation hot water systems
BS 6798:2000 Installation of gas fired hot water boilers
of rated input not exceeding 70kW
BS 6891:2005 Installation of low pressure gas pipe up to
28mm
BS 7671:2001 IEE wiring regulations
BS 4814:1990 Specification for expansion vessels
BS 5482:1994 Installation of L.P.G.
I.S. 813 Domestic Gas Installations
2.2. SITING THE APPLIANCE
The appliance may be installed in any room or indoor area,
although particular attention is drawn to the requirements of the
current I.E.E. Wiring Regulations, and in Scotland, the electrical
provisions of the Building Regulations applicable in Scotland,
with respect to the installation of the combined appliance in a
room containing a bath or shower, the location of the boiler in a
room containing a bath or shower should only be considered if
there is no alternative.
Where a room-sealed appliance is installed in a room
containing a bath or shower the appliance and any
electrical switch or appliance control, utilising mains
electricity should be situated so that it cannot be touched
by a person using the bath or shower, specifically in
accordance with current IEE Wiring Regulations.
The location must permit adequate space for servicing and air
circulation around the appliance as indicated in Section 2.4.
The location must permit the provision of an adequate flue and
termination.
For unusual locations special procedures may be necessary.
BS 6798-2000 gives detailed guidance on this aspect.
A compartment used to enclose the appliance must be designed
specifically for this purpose. No specific ventilation requirements
are needed for the installation within a cupboard.
This appliance is not suitable for outdoor installation.
The type C appliances (in which the combustion circuit, air
vent intake and combustion chamber are air-tight with
respect to the room in which the appliance is installed) can
be installed in any type of room.
Secondary ventilation is not required with this boiler. The boiler
must be installed on a solid, non-combustible, permanent wall to
prevent access from the rear.

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2.3. OVERALL DIMENSIONS
In order to allow access to the interior of the boiler for maintenance
purposes, the boiler must be installed in compliance with the
clearance requirements indicated in the diagram below.
2.4. MINIMUM CLEARANCES
LEGEND:
A= Central Heating Flow (3/4”) (22mm Copper Tail)
B= Domestic Hot Water Outlet (1/2”) (15 mm Copper Tail)
C= Gas Inlet (3/4”) ( 22mm Copper Tail)
D= Domestic Cold Water Inlet (1/2”) (15mm Copper Tail)
E= Central Heating Return (3/4”) (22mm Copper Tail)
SV outlet = 1/2” Female BSP (Not Shown)
785
310
450
FIG. 2.0
93 65
450
67 67 65 93
143
100
120
750 35
5
45
50
water
gas
310
323
225 225
130 130
F
FIG. 2.1
FIG. 2.2
After removing the boiler from its packaging, remove the
template from the separate box containing the connection kit.
NOTE: Pay particular attention to any test water that may spill
from the appliance.
Place the template in the position the appliance is to be
mounted and after ensuring it is hanging squarely, use it to mark
the holes for the hanging bracket, connection kit and flue pipe(s)
NB: For further information relating to the flue installation please
refer to Section 2.9 FLUE CONNECTION. (If the appliance is to be
fitted on a wall of combustible material, the wall must be
protected by a sheet of fireproof material).
If the appliance is to be fitted into a timber framed building,
guidance should be sought from the Institute of Gas Engineers
document REF: IGE/UP/7.
2.5.1. Drill the wall and plug using those supplied with the
connections kit, position the hanging bracket and
secure with the wall screws supplied, assemble the
connection kit and secure to the wall. NOTE:It is highly
recommended that a spirit level be used to position the
appliance to ensure that it is perfectly level.
2.5.2. Position the appliance on the hanging bracket and
connect the connection kit to the boiler connections.
(see also Sections 2.7 Gas Connections, 2.8 Water
Connections & FIG. 2.4).
For safety purposes, have a competent person carefully check
the electrical system in the property, as the manufacturer will not
be held liable for damage caused by the failure to earth the
appliance properly or by anomalies in the supply of power. Make
sure that the residential electrical system is adequate for the
maximum power absorbed by the unit, which is indicated on the
rating plate. In addition, check that the section of cabling is
appropriate for the power absorbed by the boiler.
2.5. MOUNTING THE APPLIANCE

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2.8. WATER CONNECTIONS
Legend:
A = Central Heating Flow
B = Domestic Hot Water Outlet
C = Gas Inlet
D = Domestic Cold Water Inlet
E = Central Heating Return
H = Condensate discharge
G = Condensate trap
F = Safety valve discharge
Central Heating
Detailed recommendations are given in BS 6798:2000 and BS
5449-1:1990, the following notes are given for general guidance.
P IPE W ORK :
Copper tubing to BS EN 1057:1996 is recommended for
water pipes. Jointing should be either with capillary soldered
or compression fittings.
Where possible pipes should have a gradient to ensure air is
carried naturally to air release points and water flows
naturally to drain taps.
The appliance has a built-in automatic air release valve, however
it should be ensured as far as possible that the appliance heat
exchanger is not a natural collecting point for air.
Except where providing useful heat, pipes should be
insulated to prevent heat loss and avoid freezing.
Particular attention should be paid to pipes passing through
ventilated spaces in roofs and under floors.
B Y - PASS :
The appliance includes an automatic by-pass valve, which
protects the main heat exchanger in case of reduced or
interrupted water circulation through the heating system, due
to the closing of thermostatic valves or cock-type valves
within the system.
S YSTEM D ESIGN :
This boiler is suitable only for sealed systems.
D RAIN C OCKS :
These must be located in accessible positions to permit the
draining of the whole system. The taps must be at least
15mm nominal size and manufactured in accordance with BS
2870:1980.
VIEW OF THE BOILER CONNECTIONS
G
H
FIG. 2.4
2.6. ELECTRICAL CONNECTION
The boiler operates with alternating current, as indicated in the
technical data table (Section 1.2), where the maximum absorbed
power is also indicated. Make sure that the connections for the
neutral and live wires correspond to those indicated in Fig.2.3).
The appliance electrical connections are situated inside the
electrical box (see Section 2.12).
I MPORTANT !
In the event that the power supply cable must be changed,
replace it with one with the same specifications. Make the
connections to the terminal board located within the control
panel, as follows:
- The yellow-green wire should be connected to the terminal
marked with the earth symbol; make sure to re-use the ferrule
mounted on the other supply cable;
- The blue wire should be connected to the terminal marked “N”;
- The brown wire should be connected to the terminal marked “L”.
FIG. 2.3
2.7. GAS CONNECTION
The local gas region contractor connects the gas meter to the
service pipe.
If the gas supply for the boiler serves other appliances ensure
that an adequate supply is available both to the boiler and the
other appliances when they are in use at the same time.
Pipe work must be of an adequate size. Pipes of a smaller size
than the boiler inlet connection must not be used.
Note: The diagrams for the electrical system are indicated in
Sections 2.12 and 2.13 (pages 22-24).
Warning, this appliance must be earthed.
External wiring to the appliance must be carried out by a
competent person and be in accordance with the current I.E.E.
Regulations and applicable local regulations.
The appliance is supplied with a fly-lead already connected, this
must be connected to a 240v supply fused at 3A and must
facilitate complete electrical isolation of the appliance, by the
use of a fused double pole isolator having a contact separation
of at least 3 mm in all poles or alternatively, by means of a 3 A
fused three pin plug and unswitched shuttered socket outlet both
complying with BS 1363.
The point of connection to the Electricity supply must be readily
accessible and adjacent to the appliance unless the appliance is
installed in a bathroom when this must be sited outside the
bathroom (see Section 2.2).
Should external controls be required, the design of the external
electrical circuits should be undertaken by a competent person,
see Sections 2.12 for further information.
F

9
0
100
200
300
400
500
600
700
800
0 200 400 600 800 1000 1200 1400 1600
[l/h]
[mbar]
RESIDUAL HEAD OF THE BOILER ∆T 20°C
FIG. 2.5
S AFETY V ALVE D ISCHARGE :
The discharge should terminate facing downwards on the
exterior of the building in a position where discharging
(possibly boiling water & steam) will not create danger or
nuisance, but in an easily visible position, and not cause
damage to electrical components and wiring.
The discharge must not be over an entrance or a window or
any other type of public access.
C ONDENSATE D ISCHARGE :
A flexible hose is supplied for connection to the condensate
discharge point H (Fig. 2.4). The condensate discharge hose
from the boiler must have a continuous fall of 2.5° and must
be inserted by at least 50 mm into a suitable acid resistant
tundish / pipe - e.g. plastic waste or overflow pipe. The
condensate discharge pipe must have a continuous fall and
preferably be installed and terminated within the building to
prevent freezing.
NOTE:THE FLEXIBLE CONDENSE HOSE SUPPLIED WITH THE
APPLIANCE CAN BE EXTENDED BY PULLING THE TUBE OPENING THE
RIBBED PIPE.
The discharge pipe must be terminated in a suitable position:
i) Connecting in to an internal soil stack (at least 450 mm
above the invert of the stack). A trap giving a water seal of
at least 75 mm must be incorporated into the pipe run,
there also must be an air break upstream of the trap.
ii) Connecting into the waste system of the building such as
a washing machine or sink trap. The connection must be
upstream of the washing machine/sink (If the connection
is down stream of the waste trap then an additional trap
giving a minimum water seal of 75 mm and an air break
must be incorporated in the pipe run, as above.
iii) Terminating into a gully, below the grid level but above the
water level.
iv) Into a soakway.
NOTE: If any condensate pipe work is to be installed externally,
then it should be kept to a minimum and be insulated with a
waterproof insulation and have a continuous fall.
Some examples of the type of condensate drains can be
seen on this page.
2. External termination of condensate drainage pipe via
internal discharge branch (e.g. sink waste) and condensate
siphon
3. External termination of condensate drainage pipe via
internal discharge branch (e.g. sink waste - proprietary fitting).
1. Internal termination of condensate drainage pipe to
internal stack

10
4. External termination of condensate drainage pipe via
condensate siphon
A IR R ELEASE P OINTS :
These must be fitted at all high points where air naturally
collects and must be sited to facilitate complete filling of the
system.
The appliance has an integral sealed expansion vessel to
accommodate the increase of water value when the system is
heated.
It can accept up to 7 l (1.5 gal) of expansion water. If the
heating circuit has an unusually high water content, calculate
the total expansion and add an additional sealed expansion
vessel with adequate capacity.
M AINS W ATER F EED - C ENTRAL H EATING :
There must be no direct connection to the mains water supply
even through a non-return valve, without the approval of the
Local Water Authority.
F ILLING :
A method for initially filling the heating system is supplied with
the connection kit. The filling loop is connected between the
cold water inlet and the central heating flow connections, and
incorporates a non-return valve. To operate the filling loop, it
is necessary to open both quarter turn handles, once the
required pressure has been achieved, close both handles
and disconnect the hose in accordance with water
regulations. NOTE: The installer should ensure that there are
no leaks as frequent filling of the heating system can lead to
premature scaling of the main exchanger and failure of
hydraulic components.
D OMESTIC W ATER
The domestic water must be in accordance with the relevant
recommendation of BS 5546:1990. Copper tubing to BS EN
1057:1996 is recommended for water carrying pipe work and
must be used for pipe work carrying drinking water, a scale
reducer should also be used to reduce the risk of scale
forming in the domestic side of the heat exchanger.
U NDER F LOOR H EATING S YSTEMS :
In the event of an under floor heating system, fit a safety
thermostat on the boiler flow (instructions for wiring the
thermostat to connection SP on the PCB can be found in
Section 2.12). This thermostat should be positioned at a safe
distance from the boiler to ensure the correct operation of the
same. If the thermostat is positioned too close to the boiler, the
water remaining in the boiler after domestic hot water has been
drawn will flow into the central heating system and may cause
the thermostat contact to open without there being any real
danger of the system being damaged, this would lead to a
boiler shutdown both in D.H.W. mode and C.H. mode, and the
error code “E08” would be displayed; boiler operation resumes
automatically when the thermostat contact closes on cooling.
Should the thermostat fail to be installed as recommended, the
under floor heating system can be protected by installing a
thermostatic valve upstream from the thermostat in order to
prevent the flow of excessively hot water towards the system.
WATER TREATMENT
The boiler is equipped with a stainless steel heat exchanger.
The detailed recommendations for water treatment are given
in BS 7593:1992 (Treatment of water in domestic hot water
central heating systems); the following notes are given for
general guidance;
If the boiler is installed on an existing system, any
unsuitable additives must be removed.
Under no circumstances should the boiler be fired before the
system has been thoroughly flushed; the flushing procedure
must be in line with BS7593:1992.
We highly recommend the use of a flushing detergent
appropriate for the metals used in the circuit. These include
cleansers produced by Fernox and BetzDearborn, whose

11
function is to dissolve any foreign matter that may be in the
system;
In hard water areas or where large quantities of water are in
the system the treatment of the water to prevent premature
scaling of the main heat exchanger is necessary.
The formation of scale strongly compromises the efficiency of
the thermic exchange because small areas of scale cause a
high increase of the temperature of the metallic walls and
therefore add to the thermal stress of the heat exchanger.
Demineralised water is more aggressive so in this situation it
is necessary to treat the water with an appropriate corrosion
inhibitor.
Any treatment of water by additives in the system for frost
protection or for corrosion inhibition has to be absolutely
suitable for all the metals used in the circuit.
The use of a corrosion inhibitor in the system such as Fernox
MB-1, BetzDeaborn Sentinel X100 or Fernox System Inhibitor
is recommended to prevent corrosion (sludge) damaging the
boiler and system;
If anti-freeze substances are to be used in the system, check
carefully that they are compatible with the metals used in the
circuit.
MTS suggests the use of suitable anti-freeze products such
as Fernox ALPHI 11, which will prevent rust and incrustation
taking place.
Periodically check the pH of the water/anti-freeze mixture of
the boiler circuit and replace it when the amount measured is
out of the range stipulated by the manufacturer ( 7 < pH < 8).
DO NOT MIX DIFFERENT TYPES OF ANTI-FREEZE
In under-floor systems, the use of plastic pipes without
protection against penetration of oxygen through the walls
can cause corrosion of the systems metal parts
(metal piping, boiler, etc), through the formation of oxides and
bacterial agents.
To prevent this problem, it is necessary to use pipes with an
“oxygen-proof barrier”, in accordance with standards DIN
4726/4729. If pipes of this kind are not used, keep the
system separate by installing heat exchanger
s of those
with a specific system water treatment.
IMPORTANT
Failure to carry out the water treatment procedure
will invalidate the appliance warranty.

12
E
E
2.9. CONNECTING THE FLUE
IMPORTANT!!
BEFORE CONNECTING THE FLUE, ENSURE THAT 1 LITRE OF
WATER HAS BEEN POURED INTO THE EXHAUST CONNECTION
TO FILL THE CONDENSATE TRAP (FIG.2.7). SHOULD THE TRAP
BE EMPTY THERE IS A TEMPORARY RISK OF FLUE GASSES
ESCAPING INTO THE ROOM.
FIG. 2.7
120 mm
4
Ø 60/100 mm
Fig. 2.9
FIG. 2.9
TERMINAL POSITION mm
A - Directly below an open window or other opening 300
B - Below gutters, solid pipes or drain pipes 75
C - Below eaves 200
D - From vertical drain pipes and soil pipes 75
E - From internal or external corners 300
F - Above ground on a public walkway or patio 2100
G - From a surface facing a terminal 2500
H - From a terminal facing a terminal 2500
I - Vertically from a terminal in the same wall 1500
J - Horizontally from a terminal in the same wall 300
K - Horizontally from an opening window 300
L - Fixed by vertical flue terminal
FLUE SYSTEM
The provision for satisfactory flue termination must be made
as described in BS 5440-1.
The appliance must be installed so that the flue terminal is
exposed to outdoor air.
The terminal must not discharge into another room or space
such as an outhouse or lean-to.
It is important that the position of the terminal allows a free
passage of air across it at all times.
The terminal should be located with due regard for the
damage or discolouration that might occur on buildings in the
vicinity, it must also be located in a place not likely to cause
nuisance.
In cold or humid weather water vapour may condense on
leaving the flue terminal.
The effect of such “steaming” must be considered.
If the terminal is 2.1 metres above a balcony, above ground
or above a flat roof to which people have access, then a
suitable stainless steel terminal guard must be fitted.
The minimum acceptable spacing from the terminal to
obstructions and ventilation openings are specified in Fig.
2.9.

13
Warning
The exhaust gas ducts must not be in contact with or close to
inflammable material and must not pass through building
structures or walls made of inflammable material.
When replacing an old appliance, the flue system must be
changed.
Important
Ensure that the flue is not blocked.
Ensure that the flue is supported and
assembled in accordance with these
instructions.
2.9.1 FITTING THE COAXIAL FLUE
(Ø 60 / 100 HORIZONTAL)
150 mm
* slope 5 mm per metre
150 mm
* slope
Installation without extension
Installation with extension
Fig. 2.10
Fig. 2.11
120
Level
Level
C ONTENTS :
1
X S ILICONE O-R ING (60mm)
1 X E LBOW (90
O
)
2 X W ALL S EALS (I NTERNAL &E XTERNAL )
1
X F LUE P IPE INCLUDING T ERMINAL (1 METRE - 60/100)
1 X F LUE C LAMP
1 X S CREWS
1x Seal
Once the boiler has been positioned on the wall, insert the
elbow into the socket and rotate to the required position.
NOTE: It is possible to rotate the elbow 360oon its vertical axis.
Using the flue clamp, seals and screws supplied (Fig 2.12)
secure the elbow to the boiler.
The 1 metre horizontal flue kit (3318073) supplied is suitable
for an exact X dimension of 815mm.
Measure the distance from the face of the external wall to the
face of the flue elbow (X - Fig 2.9), this figure must now be
subtracted from 815mm, you now have the total amount to be
cut from the plain end of the flue.
Draw a circle around the outer flue and cut the flue to the
required length taking care not to cut the inner flue, next cut
the inner flue ensuring that the length between the inner and
outer flue is maintained. (Fig 2.12).
e.g.
X = 555mm
815-555 = 260mm (Length to be cut from the plain end of
the flue).
Once cut to the required length, ensure that the flue is free
from burrs and reassemble the flue. If fitting the flue from
inside of the building attach the grey outer wall seal to the
flue terminal and push the flue through the hole, once the wall
seal has passed through the hole, pull the flue back until the
seal is flush with the wall. Alternatively, the flue can be
installed from outside of the building, the grey outer seal
being fitted last.

14
Fig. 2.12
2.9.2 FITTING THE 5” FLUE
(Ø 80 / 125 HORIZONTAL/VERTICAL)
Should the flue require extending, the flue connections are
push fit, however, one flue bracket should be used to secure
each metre of flue.
NOTE:SEE PAGE 19 FOR MAXIMUM AND MINIMUM FLUE RUNS.
Once the boiler has been positioned on the wall, it is
necessary to insert the Ø80/125 adaptor (FIG. 2.13) for both
horizontal and vertical flue runs into the boiler flue socket (not
supplied with flue kit - Part No 3318095).
Push the adaptor onto the boilers flue connection, grease the
seals then add extensions or elbows as required, secure the
adaptor, using the clamp and screws provided.
To fit extensions or elbows it is first necessary to ensure that
the lip seal is fitted correctly into the inner flue, once verified,
it is simply necessary to push them together, no clamps are
necessary to secure the flue components.
Before proceeding to fit the flue, ensure that the maximum
flue length has not been exceeded (See the tables on Page
19) and that all elbows and bends have been taken into
consideration, the maximum flue length is 10 metres, for each
additional 90oelbow 1 metre must be subtracted from the
total flue length, and for each 45o0.5 metres must be
subtracted from the total flue length (the height of the
vertical adaptor and a 45obend can be seen in Fig. 2.14
and a 90obend in Fig. 2.15).
NOTE:DO NOT CUT THE VERTICAL FLUE KIT.
Screws
Clamp
Seal
Fig. 2.13
Fig. 2.14 Fig. 2.15

15
NOTE:SEE PAGE 19 FOR MAXIMUM AND MINIMUM FLUE RUNS.
C ONTENTS :
1
X S ILICONE O-R ING (60mm)
1
X C ONICAL A DAPTOR (60/100mm)
1 X V ERTICAL F LUE K IT (80/125mm)
3
X S CREWS
The vertical flue kit is supplied with a specially designed
weather proof terminal fitted, it can be used either with a flat
roof or a pitched roof.
The Vertical flue kits useable lengths with the pitched roof
flashings are indicated in Fig. 2.16.
Before proceeding to fit the flue, ensure that the maximum
flue length has not been exceeded (See the tables on Page
19) and that all elbows and bends have been taken into
consideration, the maximum flue length is 4 metres, for each
additional 90oelbow 1 metre must be subtracted from the
total flue length, and for each 45o0.5 metres must be
subtracted from the total flue length (the height of the
vertical adaptor and a 45obend can be seen in Fig. 2.17).
Mark the position of the flue hole in the ceiling and/or roof
(see Fig. 2.15 for distance from wall to the centre of the flue).
Cut a 120mm diameter hole through the ceiling and/or roof
and fit the flashing plate to the roof.
DO NOT cut the vertical flue kit.
To connect the vertical flue kit directly to the boiler, place the
vertical starter kit (Part No. 3318079) (see Fig. 2.16) onto the
exhaust manifold and secure with the clamp, fit the vertical
adaptor onto the vertical starter kit (note: there is no need to
use a clamp to secure this as it is a push fit connection), the
vertical flue kit must then be inserted through the roof
flashing, this will ensure that the correct clearance above the
roof is provided as the terminal is a fixed height.
Should extensions be required, they are available in 1 metre
(Part No. 3318077), 500mm (Part No. 3318078) and 160mm
lengths, they must be connected directly to the vertical starter
kit before connecting the adaptor to allow the vertical flue kit
to be fitted. In the event that extension pieces need to be
shortened, they
must only be cut at the male end and it must
be ensured that the inner and outer flue remain flush (Fig.
2.12)
When utilising the vertical flue system, action must be taken
to ensure that the flue is supported adequately to prevent the
weight being transferred to the appliance flue connection by
using 1 flue bracket per extension.
When the flue passes through a ceiling or wooden floor, there
must be an air gap of 25mm between any part of the flue
system and any combustible material. The use of a ceiling
plate will facilitate this. Also when the flue passes from one
room to another a fire stop must be fitted to prevent the
passage of smoke or fire, irrespective of the structural
material through which the flue passes.
2.9.3. FITTING THE COAXIAL FLUE
(Ø 60 / 100 VERTICAL)
Fig. 2.16
Fig. 2.17

16
2.9.4. FITTING THE TWIN PIPE (Ø80 / 80) NOTE:SEE PAGE 19 FOR MAXIMUM AND MINIMUM FLUE RUNS.
Where it is not possible to terminate the flue within the
distance permitted for coaxial flues, the twin flue pipe can be
used by fitting a special adaptor to the flue connector and
using the aperture for the air intake located on top of the
combustion chamber.
Always ensure that the flue is adequately supported, using
one flue bracket per extension and avoiding low points. (MTS
supply suitable clamps as Part No. 705778).
To utilise the air intake it is necessary to:
1) Take the air intake cover off the top of the appliance
2) Assemble the flange on the header supplied with the boiler
3) Insert the header on the tube or the elbow up until the
lower stop (you do not have to use the washer).
4) Insert the elbow/header in the boiler air intake hole and
fasten it with screws.
The twin flue pipes can be fitted with or without additional
elbows and need no clamps, simply ensure that the red o-ring
is inserted in the female end of the flue pipe and push the
extension piece fully into the previous section of flue pipe or
elbow, check that the o-ring is not dislodged when
assembling the flue (greasing the seal will aid assembly).
Twin pipe can also be converted back to Coaxial flue to
enable vertical termination with a coaxial kit by using the pipe
bridge (Twin - Coaxial Adaptor - Part No. 3318089). When
running the twin flue pipe vertically.
It is not possible to terminate concentrically horizontally.
Termination is only possible with separate air and exhaust
terminals.
When siting the twin flue pipe, the air intake and exhaust
terminals must terminate on the same wall, the centres of the
terminals must be a minimum of 280 mm apart and the air
intake must not be sited above the exhaust terminal (refer to
Fig. 2.20). The air intake pipe can be run horizontally,
however, the terminal and the final 1 metre of flue must be
installed either horizontally or with a slight fall away from the
boiler to avoid rain ingress.
It is also strongly recommended that the air intake pipe run
be constructed of insulated pipe to prevent condense forming
on the outside of the tube.
The maximum permissible flue length for twin flue is
dependent on the type of run used.
For flue runs with the intake and exhaust pipes under the
same atmospheric conditions (TYPE 4) the maximum length is
38 metres (27kW) and 48 metres (32kW), for runs with the
terminals under different atmospheric conditions (TYPE 5) the
exhaust terminal must extend 0.5 metres above the ridge of
the roof (this is not obligatory if the exhaust and air intake
pipes are located on the same side of the building). For TYPE
5 also, the maximum permissible combined length is 51
metres (27kW) and 49 metres (32kW).
The maximum length is reached by combining the total
lengths of both the air intake and exhaust pipes. Therefore a
maximum length of 40 metres for example, will allow a flue
run of 20 metres for the air intake and 20 metres for the
exhaust pipes, also for each 90oelbow 2.2 metres must be
subtracted from the total length and for each 45oelbow 1.4
metres must be subtracted from the total flue length.
Some of the acceptable flue configurations are detailed on
page 20.
For further information relating to flue runs not illustrated,
please contact the Technical Department on 0870 241 8180.

17
Fig. 2.18
ø 100
60 mm
In the event that twin flue pipes are used, and the boiler has
a side clearance of less than 60mm from the wall, it is
necessary to cut a larger diameter hole for the flue pipe, this
should be ø10 cm, this will then allow for easier assembly of
the air intake elbow and the tube outside the wall (see Fig.
2.19). Fig. 2.19
In the event that the air intake and exhaust are run to the left,
it will be necessary to reduce the height of the air intake by
cutting 20mm from the base of the air intake elbow (see Fig.
2.18)
Coaxial
Systems
Twin Pipe
Systems
Exhaust Type
Type 1
Type 1
Types 2 & 3
Type 4
Type 5
Maximum Extension
Exhaust/Air
(m)
4 (Horizontal)
16 (Horizontal)
4 (Vertical)
16 (Vertical)
54
(Air Intake & Exhaust
Equal Lengths (27
and 27 metres)
1+56 (Air Intake 1
Metre and Exhaust 56
Metres)
Diameter
of Pipes
(mm)
Ø 60/100
Ø 80/125
Ø 60/100
Ø 80/125
Ø 80/80
Ø 80/80
Reduction
45o (m)
0.5
0.5
0.5
0.5
0.25
0.25
Reduction
90o (m)
1
1
1
1
0.5
0.5

18
EXHAUST
AIR INTAKE
AIR INTAKE
AIR INTAKE MUST NOT BE
FITTED ABOVE THE EXHAUST
Fig. 2.20
NOTE: DRAWINGS ARE INDICATIVE OF FLUEING OPTIONS ONLY.
TYPE 1
TYPE 5
TYPE 4
TYPE 3
TYPE 2
Fig. 2.19

19
FIG. 2.22
FIG. 2.21
321
GBR
54321
GBR
FIG. 2.23
DIGITAL MECHANICAL
FIG. 2.20
C2
C2
C2
2.10. FITTING THE MECHANICAL / DIGITAL
CLOCK
The ACO MFFI boiler is supplied with a factory fitted
mechanical time clock. There is a digital clock available as
an optional extra (code: 706348).
To fit the digital clock it is necessary to proceed as follows:-
1. Remove the outer casing
2. Open the control panel (see fig. 2.20);
3. Unplug the electrical connection from the PCB and unscrew
the four screws (Fig. 2.21);
4. Remove the time clock (Fig. 2.22).
5. Connect the wires supplied with the clock to the digital time
clock as shown in Fig. 2.23;
6. Reassemble in reverse order.
NOTE:THE MECHANICAL CLOCK HAS FOUR WIRES, THEREFORE THE
HARNESS WILL REQUIRE CHANGING ALSO.

20
2.11. SETTING THE MECHANICAL TIME CLOCK
2.11.1. SETTING THE DIGITALTIME CLOCK
Fig. 2.24
1. General layout
The mechanical clock covers a 24 hour period. Each tappet
represents 15 minutes A(Fig. 2.25). An override switch is
located on the clock B(Fig 2.25).
2. To set the time
To set the time of day, grasp the outer edge of the dial and
turn slowly clockwise until the correct time is lined up with the
arrow C(Fig. 2.25).
3. To Set the "On" and "Off" times
The clock uses a 24hours system. e.g. 8 = 8.00 am and
18 = 6.00 pm. "ON" periods are set by sliding all tappets
between the "ON" time and the "OFF" time to the outer edge
of the dial.The tappets remaining at the centre of the dial are
the "OFF" periods.
4. For operation
Put the selector switch Bto the symbol to control the
central heating by the clock. Put the switch Bto «I» to select
permanent operation or to «0» to turn the central heating off
permanently.
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
16
16
17
17
18
18
19
19
20
20
21
21
22
22
23
23
24
24
9
9
6
6
12
12
I
A
C
B
Fig. 2.25
Operating the time switch
The steps marked with the symbol “ ” are necessary to carry
out a switching program.
Preparing for Operation
Activate the “Res” switch (=RESET) to reset the time switch
to its default setting (activate using a pencil or similar
pointed instrument). Do this:
- every time you wish to “reset” the time switch
- to erase all switching times and the current time of day.
After approximately two seconds the following display
appears: “– – : – –”.
Enter current time and weekday
- Keep the “ ” key pressed down
During the summer time period press the +/- 1h key once.
Enter the hour using the “h” key
Enter the minutes using the “m” key
Enter the day using the “Day” key
1 = “Monday”..............7 = Sunday
- Release the “ ” key.