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Contents:
Demand Duo Principle of Operation: ................................................................................................... 3
Schematic of Demand Duo: .................................................................................................................. 4
Demand Duo Fault Finding Check List: ............................................................................................... 4
Basic operating principle of Demand Duo Thermostat: ....................................................................... 4
Types of Demand Duo Thermostats: .................................................................................................... 4
Johnson A419 Control Thermostat: ...................................................................................................... 4
Typical Wiring Diagram (DD1) Johnson A419 Thermostat: ............................................................... 4
The A419 Control Functions Explained: .............................................................................................. 4
Settings & Adjustments of Johnson A419 temperature Control:.......................................................... 4
Positioning the Jumpers: ....................................................................................................................... 4
Jumper Designations, Jumper Positions and Control Settings.............................................................. 4
JUMP1 .............................................................................................................................................. 4
JUMP2 .............................................................................................................................................. 4
P5 ...................................................................................................................................................... 4
Changing the A419 control temperature units: ..................................................................................... 4
Setting the other A419 Control functions: ............................................................................................ 4
A 419 COMONENT TEST SHEET: .................................................................................................... 4
AIMS Thermostat Control: ................................................................................................................... 4
AIMS Thermostat Temperature Dip Switches: .................................................................................... 4
Located across the top LHS of the control PCB is 8 dip switches that control the various functions of
the control. ............................................................................................................................................ 4
Pumps:................................................................................................................................................... 4
Grundfos 25-80 ..................................................................................................................................... 4
Grundfos 20-60N & Grundfos 25-80B ................................................................................................ 4
Basic System Fault Finding: ................................................................................................................. 4
Infinity Heat Source:............................................................................................................................. 4
Ringmain Pump: ................................................................................................................................... 4
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Demand Duo Principle of Operation:
Cold water enters the storage tank after passing through an isolation and non return valve. A tee is
fitted to the cold inlet pipe down stream from the non return valve. From this tee, one branch connects
to the lower inlet of the storage tank and the other branch connects to the primary (tank circulation)
pump. This pumps water to the inlet of the infinity(s) heat source. The infinity will only operate when
this pump is running.
The heated water from the infinity returns to the storage cylinder at the second lowest connection point,
located above the cold inlet.
Hot water leaves the tank from the top of the storage cylinder. This may be circulated around the
building and returned, via a ring-main pump (set) to the cold inlet after the non-return valve and before
the tee as described above.
When there is a hot water draw off, cold water enters the storage cylinder and pushes the hot water out
of the storage cylinder towards the outlet, as per any storage hot water system.
When the water temperature at the bottom of the storage cylinder drops below the thermostat set point,
the thermostat activates the primary pump(s). They draw water from the cold water feed to the storage
cylinder, or the storage cylinder itself, or a combination of both. As stated previously, this water is then
heated by the infinity and returns to the storage cylinder heated. This process is continued until the
thermostat set point is reached and the pump is switched off.
The outlet temperature setting of the infinity must be set at least three (5) degrees hotter then the
thermostat set point. Standard factory settings are: Infinity 75°C, thermostat 65°C.
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Schematic of Demand Duo:
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Demand Duo Fault Finding Check List:
Basic Demand Duo system consists of the following components
 Infinity(s) Hot Water unit
 Storage cylinder
 Electronic thermostat
 Circulating pump
Basic operating principle of Demand Duo Thermostat:
When the water temperature at the bottom of the storage cylinder drops to the pre-determined
thermostat set point (normally 60ºC), the thermostat contacts will close and provide power to the
primary circulating pump(s).
Once the primary pump(s) start, and water is drawn from the bottom of the storage cylinder and
circulated through the Infinity(s) , the flow turbines within the Infinity(s) sense the water flow and
water heating commences.
Heated water from the Infinity(s) is fed back into the storage cylinder.
It is normal for the burner on the Infinity(s) to modulate back to a low burner rate as the water
temperature within the storage cylinder rises close to thermostat set temperature.
Types of Demand Duo Thermostats:
There have been two models of thermostats used within the Demand Duo systems;

Johnson A419 Thermostat
Max current rating 1kW
Able to be adjusted to turn on or off at set temperature

AIMS Thermostat.
Max current rating 1 kW
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Johnson A419 Control Thermostat:
Operating principle.
The Johnson A419 control is a Single-Pole, Double-Throw output relay. The control features a lockable
three button touch pad for set-up and adjustment, and a liquid crystal display (LCD) which displays the
sensed temperature and other control functions.
A front panel light emitting diode, (LED) indicates the output relay status. When the relay contact is
energized and the thermostat contacts close, the LCD will be illuminated.
The control fitted to the Demand Duo cylinder will be factory locked to a set point temperature of
65oC, unless an alternative temperature has been specified for a specific job.
When the power is turned on to the thermostat, the digital display should scroll through and settle on
the temperature reading of the water within the storage cylinder.
As water is heated, the display temperature will increase to indicate current temperature of water within
the cylinder.
Johnson control has an inbuilt fault monitoring system, which can display the following faults.
Error Code
SF Flashing
alternatively with OP:
Definition
Open temperature
sensor or sensor wiring
SF Flashing
alternatively with SH
Shorted temperature
sensor or sensor wiring.
EE
Program failure
System Status
Output functions
according to the
selected sensor failure
mode. (SF Setting)
Output functions
according to the
selected sensor failure
mode (SF setting)
Output is off
Solution
See trouble shooting
section.
Cycle power to reset the
control
See trouble shooting
section.
Cycle power to re-set
the control
Reset the control by
pressing the menu
button. If problem
persists, replace the
control
Repairs & Replacement.
Do not attempt to repair or recalibrate the Johnson A419 temperature control. In the case of a
defective or improperly functioning control, the control will require to be replaced.
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Typical Wiring Diagram (DD1) Johnson A419 Thermostat:
Thermostat
Temperature
probe
Grundfos Pump
(-) Com
(+) Sen
Johnson
Thermostat
Control
A
N.C. Com
240VAC
N
E
Clipsal
Junction Box
A
N
E
240 VAC
3 pin plug
A
N
E
240VAC Supply to Infinity
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The A419 Control Functions Explained:
Set-point (SP)
The set-point establishes the temperature value at which the equipment will be switched on or off, depending on
the user selected mode of operation. Set-point range -30 to 212 –oF (-34 to 100oC) in one degree increments.
If set-point mode is set to cut-in, the set point is the temperature value at which the control closes the normally
open (N.O.) contacts. If the set-point mode is set to cut out, the set-point is the temperature at which the (N.O.)
contacts will open.
For the Demand Duo, this cut out set-point is normally 65oC.
Differential (diF)
The differential establishes the difference in temperature between the cut in value and the cut out value. The
difference is set relative to the set-point and may be between 1 to 30 oF or oC.
For the Demand Duo, this setting is the same as the factory default setting of 5oC.
Anti- Short Cycle Delay. (Asd)
The Anti-Short Cycle Delay establishes the minimum time that the output relay remains de-energized before the
next on-cycle. The Asd does not allow the output relay to re-energize until the programmed time delay has
elapsed. The delay is activated when the control is first turned on and every time an on-cycle ends. When the
display is activated, the LCD alternatively flashes the sensor temperature and the Asd. The Asd range is 0 to 12
minutes in One minute increments.
For the Demand Duo, the Asd setting is 1 minute.
Temperature Offset (OFS)
The OFS establishes a set secondary Set-point and Differential values that may be invoked to control an
application where the circuit is closed between the Binary input (BIN) and Common (COM) terminals ( and
BIN appears on the display) Offset range is 0 to 50oF or oC (in one degree increments).
A typical application might use a switching time clock to involve night-setback temperature settings.
For the Demand Duo system, this function is not used.
Settings & Adjustments of Johnson A419 temperature Control:
The Johnson A419 Temperature Controller is ‘locked ‘ at Demand Duo to a set temperature. Adjusting the UP
& DOWN buttons will have no effect on the thermostat. On normal servicing & fault finding, there is no need to
adjust the thermostat.
If ordering a new/replacement Johnson A419 temperature control as a spare part, then the control will need to be
correctly set to suit the Demand Duo system.
The touchpad cannot be unlocked without a jumper installed across the P5 jumper pins. Do not discard jumpers
in case they are required in the future.
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Positioning the Jumpers:
The P5 jumper position determines if the touchpad is locked or unlocked.
The P4 jumper pin block has two pairs of jumper pins. The top pair of pins (JUMP1) ,determines if the control
is set for heating or cooling mode. The bottom pair of pins, (JUMP2) establishes whether set-point is at cut in or
cut out.
NOTE: Make sure the Touchpad Lock jumper is installed (Unlocked) before attempting to adjust the A419
control functions.
Jumper Designations, Jumper Positions and Control Settings
Function
Cooling / Heating
Operating Mode
Set-point at
Cut-In or Cut-out.
Touch Pad Lock
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Jumper Pins
Designation on
Control
JUMP1
Top pair of pins on
Block P4
JUMP2
Bottom pair of pins
on Block P4
P5
Setting
Jumper position
Factory Default
Setting (and jumper
position)
Cooling Mode.
Jumper Removed
Cooling Mode
Removed
Heating Mode
Installed
Set-point at Cut In
Set-point at Cut
Out
Locked
Unlocked
Removed
Installed
Cut In
Jumper Removed
Removed
Installed
Unlocked
Jumper Installed
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Changing the A419 control temperature units:
The A419 control is factory set to display Fahrenheit temperature. To change to Celsius, press the UP and
DOWN arrows simultaneously.
Press UP & DOWN arrows simultaneously again to return to a Fahrenheit temperature.
Verify that the control is displaying the desired temperature units before setting the set-point.
Setting the A419 Control Set-Point.
To view & adjust set-point:
Press and hold MENU (about 2 seconds) until the display flashes ‘SP’
Press MENU again to display existing set point value.
Press UP or DOWN arrows to change set-point value. (Typically 65oC)
Press MENU again to save new value. The display will now return to the sensed temperature.
NOTE; If no set-up entry is made for 30 seconds, the control reverts to (normal) temperature display.
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Setting the other A419 Control functions:
To set the Differential, Anti sort cycle display, Temperature offset or Sensor failure operation, use the following
method.
Press and hold MENU until display changes to flashing ‘SP’. (Normally takes about 2 seconds)
Press UP or DOWN arrows repeatedly until the desired function is displayed. (see table below)
Press MENU to display the functions current value.
Press UP or DOWN arrows until the desired temperature is displayed.
Press MENU to save the new value. The display will then return to the sensor temperature.
NOTE: If MENU is not pressed after changing the setting, the new setting will not be saved and the control will
revert to the previously programmed setting values.
Display
Symbol
SP
diF
ASd
OFS
SF
Control Function
Range – Units / Value
Set point
Differential
Anti-short Cycle
Temperature Offset
Sensor Failure Operation
F or C
BIN
Temperature Units
Temperature Offset Indicator
Ice symbol
or Flame
symbol
Cooling or heating mode
-30 to 212 –oF (-34 to 100oC)
1 to 30 – (oF or oC in 1 degree increments
0 to 12 – (in One minute increments)
0 to 50 (oF or oC in 1-degree increments)
(No Range) 0 = output relay de-energized
1 = output relay energized
(No Range) - oF or oC
(No Range) – BIN is displayed and the A419
control operates on the secondary set-points
when the circuit between the BIN and COM
terminals are closed.
(No Range) Cooling mode (Ice symbol), is
displayed when the JUMP1 jumper is
removed.
Heating (Flame symbol) is displayed when
JUMP1 jumper is installed
Factory Set
Value
30
5
1
0
1
oF
N/A
Ice Symbol
Cooling
mode.
NOTE: Do not set the Set-point and Differential values, which (when their values are totaled), fall outside the
A419 control’s set-point range (-30 to 212oF or –34 to 100oC). The control will not function properly if the Cut
In or Cut Out values are outside the control set-point range.
If no setup entry is made for 30 seconds, the control reverts to the normal temperature display.
Any saved A419 control settings are non-volatile and remain in the controllers memory during power
interruptions.
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A 419 COMONENT TEST SHEET:
Hazardous Voltages.
CAUTION – RISK OF ELECTRIC SHOCK
Hazardous voltages may be present at electrical terminals and other exposed internal metal surfaces. Do
not touch any metal parts within the control when cover is removed. Any contact with metal parts
including with metal conductive tools may result in serious injury or death.
Testing if power is available to thermostat
Remove lower cover panel from storage cylinder.
Remove four (4) screws holding cover of Johnson controls
thermostat.
Carefully lift up cover. Note: Cover is attached by wiring to
PCB inside thermostat, so cover can note be removed, just
moved.
Check for 240 volt power supply on supply terminals located
under card cover.
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Testing if power is available to common
terminal on thermostat.
Check 240VAC power is available on thermostat common
terminal.
Testing if thermostat contacts have closed.
Once temperature displayed on thermostat is less than set
temperature, check for 240 VAC available on terminal
supplying voltage to pump and neutral.
Note: You should be able to hear the thermostat contact close
and control LCD illuminate when power is switched to
primary circulating pump.
If contacts have not closed, thermostat is faulty.
Replace thermostat
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Testing to see if temperature probe
is operating correctly.
Disconnect all power sources to control
Remove lower cover panel from storage
cylinder.
Remove four (4) screws holding cover of
Johnson controls thermostat.
Carefully lift up cover. Note: Cover is attached
by wiring to PCB inside thermostat, so cover
can note be removed, just moved.
Using an accurate thermometer, take a
temperature reading at the sensor location.
Disconnect sensor from control.
Check resistance of temperature probe, across
two wires.
Check measured value conforms to table below.
Temperature oC
10
20
40
60
Electrical Value
930
1000
1150
1320
If sensors measured resistance value is
substantially different from the expected value
for that temperature, check the sensor wiring.
If sensor wiring is OK, replace the sensor.
(Johnson Controls/PENN A99 temperature
sensor)
Sensor leads are not polarity sensitive.
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AIMS Thermostat Control:
Later model Demand Duo hot water systems, (DD1, DD2-4 & DD5-6) use the AIMS thermostat
controller. It is possible to change the temperature cut off point and temperature differential via dip
switches.
Thermostat to control the operation of primary pumps between storage tank and external heat source,
such as HD200 or HD250.
Circuit board is housed in a plastic box with a clear front cover. Power lead with plug, two sockets and
a temperature probe on lead leave the base of the box.
Can be set up as a DD1, where one power outlet is activated if the tank temperature drops below set
point and the other is permanently active for the HD200 or HD250 to plug into or as a DDCOMBO
where one or both power outlets are activated if the tank temperature drops below set point..
NOTE: One DD1 unit, Ensure HD Unit is plugged into correct GPO on thermostat.
Circuit board includes a display that shows measured water temperature.
“tt” indicates tank temperature when set point is reached.
“P” indicates that temperature has fallen below set point (less differential) and power to primary
pump(s) is activated.
Circuit board mounted LED is lit when power outlet is active when configured to provide power to a
pump. When set as power supply to HD, as a DD1, LED is not lit when power outlet is active.
Pump load per power outlet is maximum 1000 watts. Total power supply to run both pumps
simultaneously is 7.5 Amps. Confirm load with pump details.
Available temperature set points are 65°C, 70°C, 75°C, and 80°C.
Available temperature differentials are 3°C and 5°C.
Example: if temperature set point is 65°C and differential is -3°C pump will be switched on when
temperature is below 62°C and is switched off when temperature reaches 65°C
Start up sequence for above example will initiate then show: Lo 62, Hi 65.
AIMS Thermostat Temperature Dip Switches:
Located across the top LHS of the control PCB is 8 dip switches that control the various functions of
the control.



Dip switch position of 1 &2 control cut off temperature (65°C, 70°C, 75°C, and 80°C)
Dip switch position of switch 3 control temperature differential (either 3ºC or 5ºC)
Dip switch position of switch 7 & 8 control power point combinations
It is normal that only dip switches 1 to 3 need be altered in the field.
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Dip Switches
SW 8
LH GPO
SW 7
RH GPO
SW 3
DETA
SW 2
SW 1
Set Temp
OFF
Not Switched
OFF
Not Switched
OFF
3oC
OFF
OFF
65oC
ON
Switched
ON
Switched
ON
5oC
OFF
ON
70oC
ON
OFF
75oC
ON
ON
80oC
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Pumps:
Primary pumps on the Demand Duo system are selected to provide the most suitable water flow
through the installed Infinity(s) on the system, to provide the best performance of the system as a
whole.
As such, sequencing using either PAM Valves or a MEC’s system is not used on a Demand Duo
system.
Typical pump selection.



DD1
DD2-DD4
DD5-DD6
= 1 x Grundfos 2060N Pump
= 1 x Grundfos 2580B Pump
= 2 x Grundfos 2580B Pumps.
Check power is available to
primary circulating pump.
Grundfos 20-60N
Make sure power is isolated before
removing access covers.
Remove one (1) screw from black
plastic pump cover and remove cover.
Check for 240 volt AC across L & N
terminals See Fig 4
If power available and pump does not
operate, isolate power and check
resistance of motor windings. ( 200
between terminal L & N)
If motor windings are open/short
circuited, replace pump.
If motor windings are correct, check
pump for mechanical damage such as
seized impeller or impeller dislocated
from motor drive shaft.
Free impeller if seized, replace pump if
impeller is dislocated from motor drive
shaft.
Replacement of Pump:
Ensure water is bled through pump prior
to use.
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Grundfos 25-80
Make sure power is isolated before
removing access covers.
Remove one (1) screw from black
plastic pump cover and remove cover.
Check for 240 VAC across L & N
terminals.
If power available and pump does not
operate, isolate power and check
resistance of motor windings. ( 66
between terminal L & N)
If motor windings are open/short
circuited, replace pump.
If motor windings are correct, check
pump for mechanical damage such as
seized impeller or impeller dislocated
from motor drive shaft.
Free impeller if seized, replace pump if
impeller is dislocated from motor drive
shaft.
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Bleeding Air from Pump.
Caution, if hot water system has been
operating, the water being bled from
the pump could be very hot.
Grundfos 20-60N & Grundfos 2580B
Turn on power supply to pump.
Make sure speed selection witch is on
‘3’.
Unscrew (counter clockwise) end cap in
motor.
Allow air & water to dribble out of
bleed hole.
When all air is bled through, replace
end cap in motor.
Check for water leaks.
Positioning of Pump.
Grundfos 25-80B has the ability to
rotate the pump motor through various
positions in 90o steps.
Typically, the electrical connection and
speed selection switch can be located at
the top or either side of the pump body.
DO NOT LOCATE THE
ELECTRICAL CONNECTION &
SPEED SELECTION SWITCH
UNDERNEATH THE PUMP BODY.
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Basic System Fault Finding:
Fault
Thermostat fails to respond to call to heat water
Check & Remedy
Check power is available to thermostat by watching for
digital temperature display on thermostat LCD.
Check thermostat temperature reading is less than
thermostat set temperature. (Normally 65oC)
Check thermostat contacts have closed in response to
call for hot water. Refer component test sheet.
Thermostat displays temperature in Fahrenheit instead
of Celsius.
Check unit not recently subject to lighten storm /power
surge. Control will default to Fahrenheit when
subjected to power surge. Refer Johnson Control page
for details of re-setting control.
Pump starts and water flows, but Infinity fails to begin
purge & ignition sequence.
Check power is available to Infinity.
Check inlet water filter to Infinity is clean.
Check there is no air lock within pump. Bleed air from
pump.
Check pump has been installed with the correct water
flow direction.
Refer to Infinity fault finding in Infinity service
manual.
Pump starts, Infinity starts and then Infinity stops.
Check incoming, flowing gas supply pressure is
sufficient.
Refer to Infinity fault finding in Infinity service
manual.
Thermostat calls for heat but the pump does not start
Check thermostat contacts have closed in response to
call for hot water. Refer component test sheet.
Check pump is plugged in & turned on. (Grunfos 2580B)
Check for 240 VAC power available at pump.
Refer component test sheet.
If power is available, check for continuity of pump
windings. Refer component test sheet.
If power is supplied and pump windings show correct
resistance, check for mechanical damage such as stuck
impeller or impeller dislocated from drive shaft of
motor.
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Fault
Pump starts but there is no water flow.
Grunfos 25-80B
Remedy
Check isolation ball valve in pump connections are
turned to the ‘open’ position. Screwdriver slots should
be aligned along pipe for ‘open’ position.
Check pump has been installed with correct direction
of water flow.
Water temperature taking excessive time to recover.
Check pump impeller is spinning and not jammed or
broken.
Check water inlet filters on Infinity’s are clean.
Check all Infinity’s are operating.
Check pump speed is set on maximum speed. (Setting
3)
Check dip-switch settings on Infinity’s to ensure
correct temperatures selected. (Infinity normally set to
75oC and cylinder thermostat set temperature of
65oC)
Check correct flowing gas pressure is correct to
Infinity’s.
Noise in pump
Excessive time taken for hot water to reach hot water
outlet.
Check there is not excessive hot water being drawn
from hot water storage cylinder during recovery time.
Check all air is bled from pump.
Check for worn bearings. (Replace pump)
Check length of pipe between hot water cylinder and
hot water outlet. If excessive length, is a secondary
building circulation pump fitted.
Check power is available on building circulating
pump.
Check pump not turned off via incorrectly set time
clock.
Water Leaking from Temperature & Pressure relief
valve.
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Check secondary building circulation pump is
operating correctly.
Check incoming water pressure to system does not
exceed 850kPa. Fit cold water pressure reduction valve
if inlet pressure excessive
Check water temperature does not exceed 99oC
If pressure & temperature correct, Replace T&PR
Valve
8/23/2010
Fault
Infinity flame rod not sensing flame
Remedy
As these units can operate on a low gas flame for a
considerable period of time, the flame rod can be left
with carbon deposits which impede the flame signal. It
is important to ensure the flame rod is cleaned with
emery paper or similar to ensure a good connection
through the gas flame.
Insufficient gas to burners
Check gas inlet filter located at the base of the gas
solenoids. Small steel mesh can become blocked with
thread seal, dust etc. Inlet test point will show adequate
supply of gas, but blockage located just above inlet test
point.
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Infinity Heat Source:

Ensure that filter at water inlet is clean. Note that this is an O ring seal and does not need to be
excessively tightened. Just make sure O ring is engaged inside machined surface in brass
housing.

Ensure all Infinity’s are operating. Ensure power is available to Infinity if it is not operating.
Can check GPO with a power tool such as a drill or similar.

Many new jobs or ones where the gas supply has been modified, there may be the need to purge
the gas supply lines as they could be full of air.

All models up to late 2006: Look at flame through window for conical shape, blue base and
yellow tip. Flame height will vary if heater is modulating.

All new HD models: when operating the number displayed should be higher than the
temperature setting on the tank mounted thermostat.
o Eg Tank = 65°C, Infinity = 75°C. These are factory standard settings.
o Eg Tank = 75°C, Infinity 85°C. These are the maximum allowable settings.

All new HD models will display a fault number if one has occurred. For example, codes 11 and
12 are common for gas supply faults. Below is a full list of fault codes.

In situations where the heater fails to ignite of stay ignited, especially in windy areas there may
be low air flow through the heater. This is indicated by fault 10 in most cases. Inspect outer and
inner tubes of flue for internal heaters

Internal heaters may operate for a short period of time and then stop. This can be caused by the
co-axial flueing not being pushed together properly and exhaust gases are re-entering the inlet
air. Push the flue together to remedy this. Also inspect flue terminal for any cause to divert
exhaust air back into the inlet air.

In jobs that operate for long hours and/or in dusty or smoky environments the combustion air
fan may become dirty. Simply unplug heater and then unplug and remove fan from heater in
strict accordance to relevant Rinnai service manual. Inspect blades and clean with brush,
remembering that damaging the fan can put it out of balance and it will need replacement.

If the fan is excessively dirty the heat exchanger may also be. Remove ignition and flame
sensor leads and remove metal cover from burner section. Look up into bottom of heat
exchanger and inspect for cleanliness.
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Infinity Error Codes:
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Ringmain Pump:

These are used for circulating water around the building. They are normally either left
connected directly to a GPO to provide continuous operation or may have a time clock to switch
it off at night when the building is not in use.

These pumps do not pressurise the system when installed on the return leg, they just remove
the dead leg by circulating the water around the ring-main.

They must have a non return valve.
o Swing non return valves must be horizontal or upward as they rely on gravity to close
the valve.
o Spring check valves can be located on any plane but may contribute excessive back
pressure and restrict the pump flow rate.

Return water should only be slightly cooler than water leaving the tank. If the temperature drop
around the circuit is too high it may indicate that the ring main pump flow rate is not high
enough, and indicates a design fault or a blockage in the pipework (or poor pipework
insulation). Investigate valves and operation of pump (same procedure as primary pump).
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