Immergas ZEUS Maior User manual

ZEUS
Maior @
Wall-hung, room sealed boilers
with storage tank
ZEUS Maior @

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ZEUS Maior @
Wall-hung, room-sealed, fan-assisted boiler
with storage tank
ZEUS 21 Maior @
ZEUS 24 Maior @
General features.
ZEUS Maior @ is a wall-hung room-sealed fan-assisted boiler
(type C) with a storage tank for central heating and producing
domestic hot water.
 is boiler can be also be installed in the B22 confi guration by
using the (optional) kit.
It is equipped with an AISI 316 L stainless steel coil type stor-
age tank, with a total capacity of 60 litres, and a 2-litre d.h.w.
expansion tank (standard feature).
 is boiler is available with an output power of 21,000 kcal/h
(24.4 kW) and 24,000 kcal/h (27.9 kW) with an operation
performance higher than 90%.
Both versions feature electronic control of the ignition, tem-
perature and fl ame modulation.
With the new electronics used this boiler can be connected to
the Remote Control used for maximum simplicity.
 e hydraulic circuit is equipped with a copper water-gas
exchanger and uses the new hydraulic power unit made in
a composite material and where we fi nd the hydraulic circuit
control devices (absolute system pressure switch, adjustable system
by-pass, etc...) besides the circulator and electric 3-way diverter
valve that, according to requirements, allow boiler water to
circulate through the heating system or through the storage
tank coil to produce domestic hot water.
Combustion air intake inside the airtight chamber and the
expulsion of gases are ensured by a fan. A diff erential fl ue
pressure switch controls correct fan operation.

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Main dimensions and connections.
Legend:
G - Gas supply
R - System return
M - System delivery
RC - Recirculation (optional)
U - Hot water outlet
E - Cold water inlet
V - Electrical supply
Control panel.
Legend:
1 - Central heating selector switch
2 - Domestic hot water selector switch
3 - Burner ON yellow indicator light
4 - Boiler ON green indicator light
5 - Domestic hot water/Remote Control-Domestic Hot Water
and Central Heating-Reset Switch 0
6 - Boiler shutdown red indicator light
7 - Boiler thermometer
8 - Boiler manometer
Height (mm) Width (mm) Depth (mm)
900 600 450
CONNECTIONS
GAS SYSTEM D.H.W.
G R M U E
1/2” 3/4” 3/4” 1/2” 1/2”

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ZEUS Maior @ main components.
Legend:
1 - Testing holes (A air) - (F flue)
2 - Flue pressure switch
3 - Central heating delivery NTC probe and limit
4 - Primary exchanger
5 - Overtemperature safety thermostat
6 - Combustion chamber
7 - Automatic air vent
8 - Circulator
9 - Gas valve
10 - Motorised 3-way diverter valve
11 - System draining cock
12 - System filling valve
13 - Airtight chamber
14 - Draught diverter
15 - System expansion tank
16 - Ignition/detection electrodes
17 - Burner
18 - Domestic hot water NTC probe
19 - 316L stainless steel storage tank
20 - System water pressure switch (absolute)
21 - System 3-bar safety valve
22 - D.h.w. 8-bar safety valve
23 - Storage tank draining cock
24 - Fumes expulsion fan
25 - Pressure point, positive signal
26 - Pressure point, negative signal
27 - D.h.w. expansion tank
28 - Adjustable by-pass

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Hot water for central heating and domestic use is produced
by a primary and a secondary (d.h.w.) circuit that work as
required.
ZEUS Maior @ Hydraulic diagram.
Legend:
1 - Gas valve
2 - Stainless steel coil for the storage tank
3 - Magnesium anode
4 - Storage tank
5 - Automatic air vent
6 - Main burner
7 - Combustion chamber
8 - Primary exchanger
9 - Draught diverter
10 - Fumes expulsion fan
11 - Flue pressure switch
12 - Airtight chamber
13 - Central heating delivery NTC probe e limit
14 - Overtemperature safety thermostat
15 - Expansion tank
16 - Circulator
17 - Adjustable by-pass
18 - System water pressure switch (absolute)
19 - System draining cock
20 - Motorised 3-way diverter valve
21 - Domestic hot water NTC probe
22 - 3-bar safety valve
23 - Filling valve
24 - D.h.w. expansion tank
25 - 8-bar safety valve
26 - One-way valve
27 - Storage tank draining cock
R - System return
M - System delivery
G - Gas supply
U - Domestic hot water outlet
E - Domestic cold water inlet

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A = Head available to the system at top speed with the by-pass off
(adjustment screw tightened right down)
B = Head available to the system at top speed (screw tightened 1.5 turns
compared to the adjustment screw which is completely unscrewed)
C = Head available to the system at top speed with the by-pass open
(adjustment screw completely unscrewed)
Primary circuit (boiler circuit).
e primary circuit, with its control and safety devices, is
started each time either a central heating or domestic hot
water request is made.
Operation.
e heat contained in the fumes produced by combustion is
absorbed by the copper blades of the water-gas exchanger (8)
which, in turn, transfers it to the water circulating inside by
means of the boiler circulator (16).
e water is transferred directly to the system or it can be devi-
ated to the storage tank coil (2). is depends on what position
the electric 3-way diverter valve (20) is in which, according to
the request, either lets water flow through the system delivery
(M) and return (R) pipes or to the coil (2).
Head-flow rate graph.
e course of the curve that represents the flow rate/head ratio
depends on how the system by-pass is set which, according to
the position, gives the system a bigger or smaller head. e
characteristic curves, based on the by-pass setting, are shown
in the following graph.
Boiler circulator (1).
e pump works on the primary circuit immediately after the
3-way diverter valve to which it is connected. It is part of the
integrated multifunction unit made in a composite material.
e automatic air vent (2) is housed on the body.
Primary exchanger (1).
is is a lamellar water-gas exchanger with copper tubes and
fins (96 fins in the ZEUS 21 version and 109 in the ZEUS 24
version) and at whose outlet (delivery) both the central heat-
ing NTC delivery probe (2) and the overtemperature safety
thermostat (3) are located.
e four pipes it is made of are connected in series (4).
It is connected to the circulator delivery and to the primary
circuit delivery by push-fitted pipes (5) and O rings (6) locked
with forks (7).
Head (kPa)
Flow rate Litres/h
A
Head (m H2O)
ZEUS 21 Maior @
Head (kPa)
Flow rate Litres/h
Head (m H2O)
ZEUS 24 Maior @
B
C
A
B
C
Delivery
Return

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Motorised 3-way valve.
It is an electric 3-way diverter valve that works on the primary
circuit return and, according to the request made (d.h.w. or
heating), it lets boiler water into the central heating system or
into the storage tank coil. is depends on the position of the
shutter (5) which closes passage to the system while simulta-
neously opening it to the storage tank (d.h.w. position) or vice
versa (central heating position).
e shutter (5) is shifted into both positions when the motor
(1) is powered (1).
e hydraulic part consists of composite material (2) unit
integrating the circulator and operated by a motor (1) that
shifts it as required.
Operation.
When the central heating or domestic hot water position has
to be reached the adjustment board starts the motor (1).
When it is working, with each 180° rotation, it shifts the shut-
ter (5) and either compresses (central heating position) or releases
(d.h.w. position) the shutter counteracting spring (4).
Both the spring (4) and shutter (5) are inside the 3-way car-
tridge.
e hydraulically controlled reaching of the position requested
causes, alternately, the opening and closing of one of the two
limit microswitches (6) located inside the motor box (1).
is makes it possible to cut power off to the motor, block-
ing it in the position reached and to enable motor operation
only when a different request is made (d.h.w. or central heating
signal).
Circulator
delivery
SYSTEM
RETURN
COIL
RETURN
Storage
tank coil
return
System
return
CIRCULATOR
RETURN

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Safety devices and controls.
Adjustable system by-pass (2).
is device ensures circulation of water in the primary circuit
(between delivery and return) even when this is prevented by
the system’s high resistance.
It is mounted on the delivery manifold unit (1) and can be
adjusted by a screw, accessible from the bottom of the valve
supporting plate.
System filling device (3).
It is a ball cock mounted between the boiler circuit and the
inlet of the domestic cold water and permits pressurisation of
the central heating system.
e cock is connected to a fill-up fitting (4) which, in turn, is
connected to the motorised 3-way diverter valve unit.
System pressure switch (5).
It reads the pressure inside the primary circuit.
It is housed in the delivery manifold unit (1) and coupled to a
microswitch that prevents the burner working when pressure
is below 0.3 bar.
It prevents the main exchanger from overheating.
Automatic air vent (6).
It automatically expels any gaseous substances from the boiler
circuit.
It is mounted on the pump’s delivery side directly on the
hydraulic unit.
3-bar safety valve (7).
is valve prevents the safety pressure (3 bar) being exceeded
in the primary circuit.
It is coupled to the front of the delivery manifold unit (1) and
fixed on the outside by a fork.
When this valve triggers water exits from the delivery pipe.
System expansion tank (8).
It compensates for variations in volume as a result of heating
the water which also limits pressure variations.
It has a useful capacity of 5.9 litres (ZEUS 21 version) and 7.1
litres (ZEUS 24 version) and a pre-load pressure of 1.0 bar.
It is located at the front of the storage tank in front of the
boiler.
8
System
delivery

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Secondary circuit (d.h.w. circuit).
e domestic hot water circuit starts working whenever the
temperature of the water in the storage tank (2) has to be
taken to the value wanted, measured by the d.h.w. NTC
probe (9).
is can happen if some hot water is drawn or when restoring
pressure drops due to heat loss.
Operation.
When domestic hot water is drawn, the modulation board
starts the boiler circulator (7) working and powers the motor
of the electric 3-way diverter valve (8).
When the valve shifts into the d.h.w. position (see operation
of the electric 3-way diverter valve) the system return (R) pipe
closes and simultaneously the passage opens to the storage
tank coil (4).
is prevents circulation in the heating system while it is al-
lowed in the coil (4) which, through its walls, lets the cold water
absorb the heat contained in the primary circuit water.
In this phase the central heating function is off, the production
of domestic hot water having priority.

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Storage tank.
It is a coil type storage tank made entirely in AISI 316L stainless
steel with a total capacity of 60 litres (54 useful litres).
It is completely insulated with self-extinguishing polystyrene
and consists of an external casing closed at the bottom by a
flange secured with 12 screws.
Inside is a stainless steel concentrically spiral shaped pipe (coil)
that travels the full height of the storage tank and through
whose walls the thermal exchange takes place between the hot
water in the primary circuit and the water inside the storage
tank.
is keeps the water inside the storage tank at a constant tem-
perature and guarantees, whenever water is drawn, the instant
production of domestic hot water.
e coil can, if necessary, be taken out of the storage after
having removed the bottom inspection flange.
e following devices ensure its correct operation and integ-
rity:
Anode (1).
It is inserted inside the storage tank and protects it against
galvanic currents.
It is screwed to the bottom flange.
Polyphosphates metering unit (optional).
is prevents lime scale depositing on the coil walls.
e kit is mounted at the domestic cold water inlet.
Recirculation kit (optional).
With this kit the pipes of the domestic hot water recirculation
system (if one is installed) can be connected.
It consists of a pipe that is inserted in the storage tank after
having removed the anode with its cap.
When the kit is installed, the anode is screwed on the end of
the pipe.
Another kit is available (optional) that includes a pump (circula-
tor) for the d.h.w. recirculation system.
is kit is installed inside the space taken up by boiler and
the circulator projects slightly from under the plastic grille at
the bottom of it.
Domestic hot water NTC probe (B2) (9).
anks to this probe the modulation board can measure the
temperature of the water inside the storage tank.
It is fixed to the outside wall of the storage tank inside an
immersed holder.
Safety valve (13).
It is situated at the bottom of the storage tank by the domestic
cold water inlet.
Besides an 8-bar valve (10), that prevents the safety pressure
being exceeded inside the storage tank, it also includes:
- a filter, a storage tank draining cock with hose fitting (12)
and a one-way valve (see the hydraulic circuit, part. “5”) to
prevent the increase in pressure, resulting from heating the
domestic hot water, from causing the water to return to the
water mains.
Coil
delivery
Coil
return
11
D.h.w. expansion tank (11).
It compensates for variations in volume that result from heating
the water inside the storage tank.
It is connected to the safety valve and has a 2-litre capacity
with a pre-load pressure of 3.5 bar.
Hot
water
outlet
Cold
water
inlet

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e circuit consists of an atmospheric burner and a modulat-
ing type gas valve for gas combustion and flow regulation
respectively.
Operation.
When the main coils (3) are electrically powered both shutters
inside the valve open, letting gas through to the burner.
Consequently, the flow rate/pressure in output is adjusted by
acting on the gas valve stabiliser by means of the modulating
coil (1).
e fuel is injected into the horizontal Venturi tubes (ramps)
through the burner nozzles (7). e air-gas mixture is created
inside these tubes that is ignited by the spark of the ignition
electrodes (5).
Modulating gas valve.
e gas valve (SIT 845) features two main coils (3) controlled
by the electrical circuit, and a modulation coil (1) controlled
by the modulation board.
e maximum and minimum outlet pressures can be set with
this valve (see gas settings).
Main electric coils (3).
ey are two ON-OFF type coils powered (230 Vac) by the
ignition control unit when the burner has to be ignited.
ey are electrically connected in parallel and supplied by
mains power through a connector (2).
Modulating coil (1).
This is a low voltage coil controlled by the modulation
board.
It controls the gas valve stabiliser and allows the outlet pres-
sure to be varied in a way proportionate to the DC running
through it.
Gas circuit.
Burner.
e burner consists of horizontal Venturi tubes (6) inside which
the gas is injected by an equal number of nozzles (7) mounted
on the manifold (8).
e number of nozzles, whose diameter varies according to the
type of gas used (see technical data) are 13 in the 21,000 kcal/h
versions and 15 in the 24,000 kcal/h versions.
Ignition occurs by means of a p.c.b. (ignition control unit) that
controls both the ignition (5) and detection (4) electrodes.
Ignition electrodes (5).
ey are controlled by the ignition control unit that produces
an electrical charge between their ends, igniting the air-gas
mixture when they come into contact.
ey are at the front of the burner.
Detection electrode (4).
is is controlled by the ignition control unit and detects
burner ignition.
It is located at the front of the burner near the ignition elec-
trodes.
1
3
2

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Gas settings.
Maximum and minimum gas pressure settings are done by
means of the gas valve, observing the values shown in the tables
for the corresponding gas type (see technical data).
A differential pressure gauge is used for reading the pressure: its
positive pressure point is connected to the gas valve (4) outlet
and to the positive pressure point at the top of the airtight
chamber (see figure).
Gas valve SIT 845.
Setting maximum pressure.
Draw some domestic hot water after having put the tempera-
ture selector on maximum.
Turn the brass nut (3) clockwise to increase pressure to the
burner and in the opposite direction to reduce it.
Setting minimum pressure.
(to be done after setting maximum pressure).
After turning power off to the modulating coil, turn the screw
(2) clockwise to increase pressure to the burner and in the op-
posite direction to reduce it.
Converting the gas type.
ere are special kits for adapting to a type of gas different
to the standard one the boilers are intended for (natural gas
or LPG).
Conversion consists in changing the burner nozzles and moving
the “NATURAL GAS-LPG” jumper (S1) on the modulating
board.
Maximum and minimum d.h.w. pressures are then set on the
gas valve in the way described above.
Maximum and minimum output in the central heating mode
and burner ignition pressure (see the table below) are set by way
of the relative trimmers mounted on the modulating board (see
modulating board operation).
Soft ignition values mm H2O
Natural gas LPG
ZEUS 21 Maior @ 25 70
ZEUS 24 Maior @ 25 65
Legend:
1 - Coil
2 - Minimum output adjustment screw
3 - Maximum output adjustment screw
4 - Gas valve outlet pressure point
5 - Gas valve inlet pressure point
6 - Protection cap
SIT 845 valve

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Flue circuit.
Operation.
e products of combustion, after hitting the water-gas ex-
changer (2), are conveyed to a hood (4) on top of which the
fumes extractor (5) is fitted (fan).
Fan operation ensures the forced expulsion of the fumes and,
at the same time, creates a vacuum in the airtight chamber (3)
so the combustion air can be aspirated from outside.
Correct fume extraction is controlled by a differential flue
pressure switch (6); when it trips it either enables or prevents
burner ignition.
Air/fumes testing holes (7-8).
ere are two holes with screw closing on the top of the outside
of the airtight chamber which can be accessed from the front;
they are used to sample combustion air (7) and fumes (8).
Signal pressure points, flue pressure switch (9-
10).
ere are two pressure points with screw closing on the top
of the outside of the airtight chamber. e signal at the ends
of the flue pressure switch (6) can be measured by means of
these points.
e positive pressure point (10) is connected to the inside of
the airtight chamber.
Likewise, the negative pressure point (9) is coupled to a Y-
shaped pipe (11) that, in turn, is connected to the draught
diverter (4) and to the negative pressure point of the flue
pressure switch (6).

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Flue pressure switch (6).
It is located at the top, inside the airtight chamber and, by
means of the relative points, measures the difference in pres-
sure between the top of the draught diverter (where the fan
is installed and works) and the inside of the airtight chamber
itself.
e signal measured by the pressure switch varies according
to the length of the intake/exhaust ends and can be measured
by the relative pressure points located at the top of the airtight
chamber (9-10).
When the switch trips it causes a contact to switch that enables
or prevents burner ignition.
Triggering pressures
flue pressure switch
ON
Pa (mm H2O)
OFF
Pa (mm H2O)
ZEUS 21 Maior @ 36 (3.7) 44 (4.5)
ZEUS 24 Maior @ 52 (5.3) 42 (4.3)
Fan (5).
e extractor works downstream from the combustion cham-
ber and is secured vertically to the top of the hood (4) from
which it extracts the fumes, conveying them to the exhaust
pipes to which the boiler is connected. It guarantees the flow
of air inside the airtight chamber at the same time.
It is controlled by the adjustment board and basically its opera-
tion coincides with that of the burner.
Extraction and exhaust systems.
(see the extraction and exhaust ends instructions).
ZEUS Maior @ is designed to be connected to the intake/
exhaust coupling pipes and can be installed in the airtight
chamber or fan-assisted (type C) configuration or, with the kit,
in the open chamber fan-assisted (type B22) configuration.
As regards to the head losses of each accessory, for the various
possible combinations and use of the diaphragms to install ac-
cording to pipe length see the instructions for the extraction
and exhaust ends (boiler instruction booklet).
e accessories (curves, extensions and end pieces) are the couple-
on type and silicone lip seals guarantee sealing.
Open chamber and fan-assisted configuration
(type B22).
Using the relative kit, the open chamber fan-assisted configura-
tion of the ZEUS Maior @ boiler (type B22) can be installed
which means combustion air is extracted directly from the
room.
Extraction.
e air is aspirated exploiting the hole at the top of the air-
tight chamber and on which, after first fitting the seal (1),
the wind diverter (2) is mounted with the exhaust flange (3)
screwed on it.
Exhaust.
e flange used in split systems is used here to connect to the
80 mm diameter exhaust pipes.
By using the accessories you can have either a horizontal (A)
or vertical (B) exhaust type.
To ensure the boiler works correctly a 49 Ø (4) diaphragm
must be mounted between the exhaust coupling and the
flange (5).
To avoid condensation problems the exhaust pipe must be no
longer than 5 straight metres in the case of normal pipes
and 12 straight metres if they are insulated.
e maximum permitted length is 12 straight metres.
Airtight chamber fan-assisted configuration
(type C).
(See EOLO Maior @).
Extraction and exhaust kit.
(See EOLO Maior @).

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Electrical circuit.
e electrical circuit of the ZEUS Maior @ boiler is controlled
100% by a microprocessor controlled p.c.b. which controls
boiler functions.
230 V AC circuit.
Safety devices and controls.
Some of the control and safety devices work at mains voltage
(230 Vac) while others at low voltage.
It detects burner ignition, being hit by its flame.
It’s connected to the ignition control circuit’s detection circuit.
Detection electrode
(E3)
It interrupts power to the circuit when power input is over 3.15 A.
It is mounted on the modulation board.
Fuse
(F)
Fuse
3,15 AF 250 V
Legend:
B1 - NTC delivery probe
B2 - Domestic hot water NTC probe
CAR - Remote control (optional)
CZ - Zone control unit (optional)
E1-E2 - Ignition electrodes
E3 - Detection electrode
E4 - Safety thermostat
F - Line fuse
H1 - Gas supply valve LED
H2 - Block indicator LED
H3 - Mains LED
M1 - Circulator
M2 - Fumes fan
M3 - 3-way diverter valve
S4 - Flue pressure switch micro
S5 - Main switch
S7 - System pressure switch
TA - Room thermostat On/Off (optional)
X20 - TA or CAR inhibition jumper
Y1 - Gas valve
Y2 - Gas valve modulator
F
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It acts on the ignition control unit and enables burner operation
when the fumes are expelled correctly.
When closed and with the fan off, it does not enable the start of
the ignition cycle.
Flue pressure switch
(S4)
Changing
contact
When the safety temperature is exceeded (105°C) it cuts power off
to the main gas valve coils (Y1).
It is located at the main exchanger outlet.
Safety thermostat
(E4)
Clicson thermo-
stat with normally
closed contact
Loads.
It is controlled by the modulation board when there is a burner ignition request.
It controls the devices necessary for ignition (fan, main gas valve coils, ignition electrodes)
and for detecting the flame (detection electrode).
Ignition control unit
(IGN. BOARD)
It is powered when the main switch is on (summer) or (winter) (see modula-
tion board operation).
Modulation board
It is powered by the modulation board when there’s a d.h.w., central heating or antifreeze
request.
It permits circulation in the primary circuit.
Boiler circulator (M1)
It is powered at mains voltage by the ignition/detection control unit when it is necessary
to ignite the burner.
It allow gas to flow to the burner.
Gas valve (Y1)
(main coils)
ey are controlled by the ignition control unit that causes a spark at their ends which
ignites the air-gas mixture.
Ignition electrodes
(E1)
It ensures the flow of air inside the airtight chamber and the exit of fumes produced by
combustion.
It is powered by the ignition control unit.
Fan
(M2)
With this valve the flow of primary circuit water can be diverted from the central heating
system to the storage tank coil and vice versa.
It is powered by the modulation board.
Electric 3-way diverter
valve
(M3)

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Low voltage circuit.
anks to this unit the boiler can work with 3 zone valves or external
pumps controlled by the relative room thermostats.
Zone 1 is controlled (times and temperatures) by CAR (if in-
stalled).
Zones control unit (CZ)
(external optional)
is device is to control the boiler remotely (SUMMER / WINTER
switch, setting and indicating temperatures, displaying alarms, resetting,
etc.) and acts as a weekly timer/room thermostat.
Remote Control
(CAR)
(external optional)
See Remote Con-
trol operation
(CAR)
See zones control
unit operation
Depending on the position it is in it allows:
0 Low voltage circuit not powered.
( ) D.h.w. and CAR operation (optional).
( ) D.h.w. and central heating operation.
RESET Resets after an ignition failure or if the overtemperature
safety device trips (the RESET position works at mains voltage closing
a contact that acts on the ignition control unit).
Main switch (S5)
Double 3-posi-
tion switch + reset
push button
It lets the modulation board measure the temperature of the delivery
water in the primary circuit.
If it breaks the burner stops working whether in the central heating
or d.h.w. mode.
It is located on the main exchanger outlet.
Delivery probe
(B1)
NTC probe
10 kohm 25°C
It lets the modulation board measure the outlet temperature of the
hot water in the storage tank.
If it breaks its stops the burner working in the domestic hot water
mode.
It is inside a hole on the outside wall of the storage tank to which
it is fixed.
D.h.w. probe
(B2)
NTC probe
10 kohm 25 °C
It enables operation in the central heating mode when room tem-
perature is below that required.
If CAR is installed the thermostat has to be disconnected without
restoring the X20 jumper.
Room thermostat (TA)
(external optional)
Interrupted
contact
It is powered by the modulation board with a variable continuous current.
It allows gas pressure to the burner to be varied.
Gas valve modulator
(Y2)
Loads.
It acts on the modulation board cutting power off to the circula-
tor (M1) and to the ignition control unit when the pressure in the
boiler circuit is below 0.3 bar.
System pressure switch
(S7)
Interrupted
contact

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Electrical circuit.
Central heating phase.
Working with the room thermostat.
When the main switch (S5) is in the “WINTER” position it
powers the modulation board and enables operation in the
central heating mode.
When the contact of the room thermostat (TA) closes the low
voltage circuit starts the boiler circulator (M1) working when
the K1 relay contact closes.
In the meantime, the adjustment circuit causes the relay K3
contact to deviate, that powers motor (M) of the 3-way valve
(M3), and keeps working until limit switch “N” opens when
the central heating position is reached.
If the system pressure switch (S7) measures a pressure in the
primary circuit that is higher than the minimum value (con-
tact S7 closed) and if the temperature measured by the NTC
delivery probe (B1) is below that set on the control panel with
the central heating potentiometer, the board sees to closing the
contact of the request relay K2.
is causes the control unit (IGN.BOARD) to start the igni-
tion cycle, that first checks the correct position of the flue
pressure switch (S4) (“NC” position) and then it powers the
fan (M2).
After the flue pressure switch contact (S4) has switched (“NO”
position) caused by the fan working (M2), the control unit
(IGN.BOARD) first powers the ignition electrodes (E1-E2)
followed by, with the safety thermostat (E4) enable, both gas
valve coils (Y1).
Burner ignition is detected by the control unit (IGN. BOARD)
by means of the detection electrode (E3).
Using the Remote Control.
When the main switch (S5) is in the “SUMMER” or “CAR”
position it powers the modulation board and the Remote
Control (CAR).
If the conditions detected by the Remote Control (CAR)
require ignition in the central heating mode (the CAR SUM-
MER/WINTER selector on WINTER, heating temperature set-
ting higher that what is read by the delivery probe (B1), hourly
programmer request, room temperature setting higher than what
is read), the board powers the boiler circulator (M1) by means
of the K1 relay contact and burner ignition occurs as described
above.
Note: In both cases, every time the unit switches off because the
temperature is reached, the modulation board stops the burner
working in the central heating mode for 180 seconds which can
be reduced to 30 seconds via the jumper S2 (see modulation board
operation).
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Electrical circuit.
Domestic hot water phase.
Operation.
When the main switch (S5) is in the “SUMMER” or “WIN-
TER” position it powers the modulation board and enables
operation in the domestic hot water mode.
If the temperature measured by the domestic hot water NTC
probe (B2) is below the temperature set on the control panel
(or on CAR if mounted), the adjustment circuit starts the boiler
circulator (M1) when the K1 relay contact closes.
In the meantime, the adjustment circuit switches the relay
K3 contact that powers the 3-way diverter valve (M3) motor
(M) which keeps working until limit switch “A” opens which
occurs when the d.h.w. position is reached.
If the system pressure switch (S7) measures a pressure in the
primary circuit that is higher than the minimum value (contact
S7 closed), the board sees to closing the contact of the request
relay K2.
As a result, the control unit (IGN. BOARD) starts the igni-
tion cycle, first of all checking the correct position of the flue
pressure switch (S4) commutator (“NC” position) and then
powering the fan (M2).
After the contact of the flue pressure switch (S4) has switched
(“NO” position) due to the fan (M2) working, the control unit
(IGN. BOARD) first powers the ignition electrodes (E1-E2)
followed by, receiving the
safety thermostat (E4) enable, both gas valve coils (Y1).
Burner ignition is detected by the control unit itself (IGN.
BOARD) by means of the detection electrode (E3).
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