Rinnai RHFE-308 FTR User manual

Installation and User Manual
RHFE-308 FTR
RHFE-308 FTR
Energysaver Space Heater
Important.
Read these instructions carefully before attempting installation or use of
this appliance. All work must be carried out by competent persons.

– 2 –
CONTENTS
Getting to Know your RHFE-308 FTR ………………………………………………………………………3
Remote Control …………………………………………………………………………………………………4
Control Panel Layout …………………………………………………………………………………………5
Features …………………………………………………………………………………………………………6
Safety Points ……………………………………………………………………………………………………8
Operating your new RHFE-308 FTR ………………………………………………………………………10
Setting the Clock ………………………………………………………………………………………………14
Pre-heat ………………………………………………………………………………………………………17
Override Function ……………………………………………………………………………………………18
Caring for your new RHFE-308 FTR ………………………………………………………………………19
Error Messages ………………………………………………………………………………………………21
Installation Instructions ………………………………………………………………………………………22
Location ………………………………………………………………………………………………………24
Installing the Flue ……………………………………………………………………………………………27
Sleeve and Manifold Installation ……………………………………………………………………………29
Flue Extension Kits ……………………………………………………………………………………………32
Conversion ……………………………………………………………………………………………………36
Connecting Gas and Electrical Services ……………………………………………………………………37
Testing …………………………………………………………………………………………………………38
Gas Pressure Setting …………………………………………………………………………………………39
Block and Wiring Diagram ……………………………………………………………………………………42
Dimensions ……………………………………………………………………………………………………44
Specification……………………………………………………………………………………………………46
Service Contact ………………………………………………………………………………………………48

–3 –
GETTING TO KNOW YOUR NEW RHFE-308FTR
REMOTE CONTROL
BRACKET
ROOM
TEMPERATURE
SENSOR
GAS CONNECTION
ELECTRICAL CORD
HUMIDIFIER TRAY
Built into the warm air
discharge duct.
Humidifies the warm
air flow.
BOTTOM TRIM
Pulls off to allow filling
of humidifier tray.
ON/OFF SWITCH
CONTROL PANEL
Concealed panel with
clock, room and pre-
set temperature
selection.
Time, temperature
and appliance error
codes are shown
here.
AIR FILTER
Helps to protect the
interior of the
appliance and fan
from dust particles.
EXHAUST OUTLET
Exhausts flue products
to the outside of the
building.
AIR INLET TUBE
Carries air for
combustion.
FLUE SYSTEM
(Supplied Separately)
LOUVRE
Warm air discharge
duct.
Rinnai Corporation - Japan
Manufactured under a
Quality System Certified
as complying with ISO
9001 by an Accredited
Certification Body.
ISO 9001
APPROVED BY JIA

–4 –
REMOTE CONTROL
ON
OFF
OFF BUTTON
Stops heater manually.
TEMPERATURE
ADJUSTMENT
Increases or decreases
the temperature setting.
ON BUTTON Operates the heater manually.
C
R
2
0
3
2
OPEN
TO REPLACE BATTERY Simply open the back of the remote control and replace Lithium battery. TYPE: CR 2032
BATTERY Power source for operating remote control.
FRONT REVERSE
■NOTE
>Some fluorescent lights may interfere with the transmission of remote control signals, in this case
changing the position from which you are operating the remote control may help.
>Avoid leaving the remote control in direct sunlight and do not place the remote close to the louvres
of the heater.
>Avoid getting the remote control wet, or dropping it.
>The remote control works within 5 metres and an angle of 40˚to the receiver on the heater.
>Only use the battery type specified. (CR 2032).
>Remove battery if control is not going to be used for a long period. This will help to avoid damage
from leaking batteries.

–5 –
Child Lock
Timer 1
Economy
Timer 2 Override
AM PM
Set ・Room
Temp
・
Time Set times
Clock Timer 1 Timer 2
Filter
on off
ON / OFF
ON
CONTROL PANEL LAYOUT
ECONOMY
Selects energy saving function.
CHILD LOCK
Locks all controls when pressed. (EXCEPT OFF)
SET TIMES
Selects clock and/or Timers for adjusting or programming.
REMOTE CONTROL
RECEIVER
TIME/TEMP ADJUSTMENT
Increases or decreases the temperature setting as well as changing hours or minutes.
CHILD LOCK
INDICATOR
Indicates Child lock is activated.
TIMER INDICATOR
Indicates that Timer 1 or Timer 2 has been selected to operate.
OVERRIDE
Temporarily changes operation from ON to OFF or OFF to ON, until next programmed setting is reached.
ECONOMY
INDICATOR
Indicates that the Economy mode is in operation.
OVERRIDE
INDICATOR
Indicates that the override function is activated.
ON TIMER
Selects operating mode for Timer 1 or 2.
ON/OFF BUTTON
Main switch for turning ON/OFF.
TIME/TEMP DISPLAY
Shows either the time of day, temperatures, or coded error messages.
POWER ON/COMBUSTION
INDICATOR
Indicates that the appliance is turned ON and whether the burner is alight.
FILTER INDICATOR
Indicates that the filter needs cleaning.
CLOCK ADJUSTMENT AND
TIMER INDICATORS
Indicates that clock or dual timer programme is being set.

–6 –
FORCED FLUE SYSTEM PUSH BUTTON IGNITION
Air for combustion is taken from outside the
room and the flue products are exhausted
outside, keeping the room air clean.
Only one touch of the ON/OFF switch is
required to operate the heater.
EXHAUST
AIR
INLET
PRE-HEAT
The function will automatically operate the
appliance within one hour prior to the
programmed time of the Timer. This is
designed to heat a room to the pre-set
temperature by the programmed time.
WARM AIR DISCHARGE
Warm air flows from the bottom of the
appliance through the louvres, assisting in
even heat distribution. An integral humidifier
tray is built into the warm air discharge duct.
ONE
TOUCH
DUAL ON/OFF TIMER
The Dual Timer allows you to programme
the appliance to come on for two separate
periods each day, usually one period in the
morning, and one period in the evening.
The built in Intelligent Mode brings the room
temperature to the temperature you have
selected, by the time programmed into the
Timer.
The Dual Timer feature means that you can
“Set and Forget”your heater. It will turn
itself ON and OFF at times you have
programmed until you cancel the Timer
program.
FEATURES

–7 –
MEMORY
The micro-computer records selected pre-
set temperatures, the times programmed
into the Timers as well as operating the
Economy and Intelligent modes, to maintain
comfort levels.
FILTER INDICATOR
When the fan filter becomes covered with
dust and the temperature inside the
appliance rises, the filter indicator will flash.
The filter should be vacuumed at regular
intervals to avoid unnecessary strain on the
appliance.
FITERINDICATOR
REMOTE CONTROL
For the convenience of turning the heater
ON or OFF, as well as adjusting the
temperature up or down while at a short
distance from the heater.
ON
OFF
ECONOMY MODE
This is an energy saving feature designed to
reduce the room temperature to 1˚C less
than the pre-set temperature over a period
of 30 minutes, and an additional 1˚C after
another 30 minutes.
PRE-SET
TEMP
2C
1hour
￡
AUTO COMFORT
Ensures that the flow of warm air from the
louvres is maintained at a comfortable
volume during the warm-up period by a 8
step modulating convection fan, in
conjunction with the thermostat, reducing
cool draughts.
CHILD LOCK
When the Child lock is activated all controls
other than the OFF switch will be locked.
Deactivating the lock releases the controls.
If the lock is activated when the appliance is
off, all functions will be locked.
LOCKED

–8 –
SAFETY POINTS
Do not restrict the warm air discharge by
placing articles in front of the heater.
This appliance must not be used for any
purpose other than heating.
Do not spray aerosols whilst the heater is
operating. Most aerosols contain butane gas,
and can be a fire hazard if used near this
heater when it is in use.
Flue guard is recommended where children
may be able to touch the flue terminal.
Do not allow curtains or other flammable or
combustible materials to come into contact
with the heater.
Combustible materials must not be placed
where the heater could ignite them.
Do not allow anyone to sit on or lean against
the appliance.

–9 –
SAFETY POINTS
Keep flammable materials, trees, shrubs, etc,
away from the flue terminal.
Do not allow anyone to post articles through
the louvres.
LPGAS
GAS
Gasoline
Filter should be cleaned at regular intervals. Young children should be supervised at all
times. Hand or body contact with the louvres
should be avoided.
Do not place articles containing liquids on top
of the heater. Liquids spilt on the controls may
cause extensive damage.
Do not allow young children or the infirm to
sleep directly in front of the heater.
Clean with vacuum cleaner, weekly.

–10 –
OPERATING YOUR NEW RHFE-308FTR
■TO OPEN THE CONTROL PANEL
Lift lightly in the centre of the lid where there is
a catch. The control panel lid will then drop
backward to an angle.
■TURNING ON
Press the ON/OFF button to operate the
heater. The ON indicator will glow green.
After approximately 20 seconds the spark
generator will be heard before the burner
ignites and the ON indicator glows red,
indicating that the burner is alight. Warm air
can be felt coming from the louvres 15
seconds later.
If the heater does not ignite on initial use, this may be due to air remaining in the gas supply line. The
spark generator will only continue for 15 seconds. After this it will be necessary to press the ON/OFF
button OFF, then ON again.
■TURNING OFF
Simply press the ON/OFF button to switch off
the heater. The ON indicator will go out. The
convection fan will continue to operate for
several minutes after the burner has gone out
in order to cool the appliance. Do not unplug
the appliance while the convection fan is
running.
DO NOT turn heater off by unplugging at the power point.
The convection fan must continue to run until the appliance cools.
LIFT
Filter
ON / OFF
ON
Filter
ON / OFF
ON

–11 –
■ROOM TEMPERATURE ADJUSTMENT
■ECONOMY MODE
The room temperature and pre-set temperatures can only be displayed and adjusted when the heater is
running.
If the heater does not ignite then the pre-set temperature may not be set to a setting which is higher
than the room temperature. The ON indicator will change colour from red to green when the heater
reaches the pre-set temperature and stops runnning.
The Economy mode may only be operated when the heater is turned on, but remains in the system
memory once set until deactivated.
Select the Economy mode before selecting time operation.
1
Press the “”button to increase the temperature
setting or “”button to decrease the temperature
setting.
The Temperatures can be preset to:
a) [ L ] low (about 10˚C)
b) [16˚C] to [26˚C] in 1˚C steps
c) [ H ] (continuously high)
1
Press the Economy button to start the Economy
function. The Economy indicator will glow.
Child Lock Timer 1 Economy
2
Press the Economy button once more to switch off
the function.
After the room is heated initially the air temperature
may be dropped to a lower level without affecting
comfort. 30 mins after the selected room temperature
(set with the thermostat) is reached, the Economy
mode, if set, reduces the temperature by 1˚C. After
another 30 mins it reduces the temperature by a
further 1˚C, this is an energy saving feature. The
Economy mode does not operate if the heater is
under capacity for the room size.
Child Lock Timer 1 Economy
Presettemperature
1°reduction
1°reduction
30min 30min
AM
PM
Set ・Room
Temp
・
Time

–12 –
■CHILD LOCK
■AUTO COMFORT
A room temperature sensor located at the rear of the appliance is continuously monitoring the temperature
of the room. The main purpose of Auto Comfort is to improve control over the flow of warm air being
discharged through the louvres when the heater is first operated. The means by which this control is
achieved is a 7 speed modulating convection fan and the temperature sensor, in conjunction with a micro-
computer.
In order to achieve comfortable heating, it is preferable to avoid cold draughts from the appliance. In the
case of a conventional fan heater, the convection fan operates normally from the time of ignition and a
cool draught may accompany the flow of air from the appliance.
To overcome this situation, fuzzy logic controls the speed of the convection fan after taking into
consideration the room temperature at the time of ignition. For example: the room temperature is low,
then the fan rotates at low speed. As the room temperature rises the speed of the convection fan
gradually increases.
In this way it is possible to ensure a comfortable flow of warmed air, as well as decreasing the sensation
of cold draughts immediately after ignition.
The convection fan speed increases proportionally as the room gradually heats up. This improves the
warm air distribution, assisting in a reduction of warm air stratification throughout the room, and resulting
in more effective heating conditions.
The micro computer continuously monitors the room temperature and adjusts the covection fan speed
according to the conditions at the time.
The Child lock will help to prevent accidental operation as well as small children from altering the
controls.
During normal operation the Child lock may be activated and all controls other than the OFF switch will
be locked. Deactivating the lock releases the controls. If the lock is activated whilst the heater is turned
OFF, then all functions will be locked. If the heater is turned OFF whilst the Child lock is activated, it
cannot be turned ON again until the lock is deactivated.
1
To operate the Child lock simply press the Child Lock
button. The function is activated immediately and the
Child lock indicator will glow.
Child Lock Timer 1 Economy Timer 2 Override
2
To deactivate the Child lock simply press the Child
Lock button for 2 seconds and the Child lock indicator
will go out. The lock can be deactivated at any time
in this way.
Child Lock Timer 1 Economy Timer 2 Override

–13 –
■FAN FILTER
To protect the room air fan from dust particles or lint, a
filter is situated at the rear of the appliance. When
this filter becomes blocked, the filter indicator will flash
to indicate that it should be cleaned. Clean the filter
weekly during the heating season to avoid
unnecessary strain on the appliance.
Do not remove filter when appliance is operating.
When the filter requires cleaning, clean filter before
using the appliance, or whilst the appliance is not
operating.
If you do not clean the filter at regular intervals and
the filter indicator is allowed to remain flashing, then
the appliance will stop and [14] will flash on the Digital
Display signifying that the inbuilt safety device has
functioned. You must clean the filter before operating
the heater again.
■HUMIDIFIER TRAY
■VERTICAL LOUVRE ADJUSTMENT
The warm air flow direction may be altered by
inserting a screwdriver or similar tool and gently
bending the vertical louvre(s) either to the left or the
right.
Note: These louvres are not designed to be
adjusted more than 6 times.
So that you can humidify the air, your Rinnai RHFE-308FTR is fitted with an enamelled tray at the
bottom of the heater. If you choose to make use of the humidifier tray, it will need filling about once a
day during the heating season. Do not fill the humidifier tray while the heater is running.
The humidifier has the benefit (when filled with water) of raising the humidity in the air. With increased
humidity, the heater can actually be run at a lower temperature while still maintaining the same level of
comfort.
1To fill the humidifier tray:
Remove the bottom trim panel, below the louvres, by
pulling on both sides. Simply pull the tray forward to
allow it to be filled with water. The warm air will be
humidified as it passes over the water in the tray.
Refit the bottom trim panel after filling the tray. The
RHFE-308FTR is a very high efficiency appliance,
during operation a small amount of condensation is
produced in the flue system, this drains into the
enamelled humidifier tray.

–14 –
SETTING THE CLOCK
When the appliance is first plugged in and then turned on, the Digital Display will show .
As an example, let’s set the clock to 10:35 am.
OPEN THE CONTROL PANEL - SEE PAGE 10.
1
When the appliance is first plugged in or after a
power failure, the Digital Display will show .
Press the Set Times button once, the Clock Indicator
will flash.
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
2
Press and hold the “”button; the minutes will
begin to change first, then the time will change by
whole hours. Release the button when AM 10:00
shows on the Digital Display. Confirm that you have
selected AM, a small indicator on the left hand side of
the Digital Display indicates the AM setting.
Press and hold the “”button again, release the
button when AM 10:35 shows. If you go past AM
10:35, then the “”button can be used to change
the time settings in reverse.
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
3
Press the Timer Set button five times to lock in and
complete setting the time. The Clock and Timer
indicators will go out. A small indicator on the Digital
Display will flash to show that the clock is operating.
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
DIGITAL DISPLAY
TIMER/CLOCK SET
ON-OFF SWITCH
ON-OFF SWITCH INDICATOR
TIMER/CLOCK SET INDICATOR
TIMER/TEMP ADJUSTMENT

–15 –
PROGRAMMING THE ON/OFF TIMER(S)
Before programming the Timers you must ensure that the clock has been set to the correct time.
See page 14.
TIMER 2 is programmed in the same way, remember to ensure that the Timer 2 indicator is flashing
when you programme in the desired setting.
The Timers can be programmed to operate for any two periods in any 24 hours. Turn to next page to
operate the dual timer.
The programmed time must be selected and locked-in within one minute of the On Timer indicators
flashing otherwise the programmed times will not be retained in the system memory.
1
Press the Set Times button twice. The Digital Display
will show AM 6:00. Timer 1 indicator will flash.
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
2 Override
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
2
Press the “”button until AM 7:00 appears, release
the button, then press it again until AM 7:10 appears.
(Press the “”button if you go past AM 7:10.)
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
3
Press the Set Times button again, the Timer 1 OFF
indicator will flash. Press the “”button until AM
9:00 appears.
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
4
Press the Set Times button three times to lock in the
programmed time. The Digital Display will show the
current time. A small indicator on the Digital Display
will flash to show that the Display has returned to the
clock.
AM
PM
Set ・Room
Temp
・
Time Set times
Clock
Timer 1
Timer 2 on off
As an example let’s programme Timer 1 to heat the room by 7:10 AM and finish at 9:00 AM.
TURN TO NEXT PAGE TO OPERATE THE TIMERS.

–16 –
OPERATING THE TIMER(S)
Before operating the Timer(s), the clock time must be correct, and a starting time and finishing time for
the Timer(s) must be programmed. See pages 14 and 15. The two Timers operate in the same way.
This heater does not commence operation at the programmed starting time. It will attempt to heat a
room by the programmed starting time. See Pre-heat page 17, for further explanation.
If there is a power failure, the system memory will retain the Timer programs, and the clock will stop at
the time the power goes off. The clock will start again when the power comes back on, but the time will
be slow by the duration of the power failure. To set the clock to the correct time after the power has
come back on, simply follow the instructions on page 14.
1
To select the Timer(s) to commence heating:
Check the time shown on the Digital Display is
correct. See page 14. Check the ON and OFF
times, for both Timers if neccessary, see page 15.
AM
PM
Set ・Room
Temp
・
Time
2
Press the ON-OFF button to operate the heater. The
On indicator will glow green and the heater will begin
to operate. Select the desired temperature setting.
Filter
ON / OFF
ON
3
Press the Timer 1 and/or Timer 2 button(s).
The Timer indicator(s) will glow and the heater will
remain on standby until one hour prior to the time
programmed into the selected Timer(s) is reached.
When this time is reached, the Timer indicator will
flash and the heater will operate. The ON indicator
glows red when the heater commences operation.
Child Lock Timer 1 Economy Timer 2 Override
SET AND FORGET OPERATION
Your heater can be operated to alternate between Timers automatically during cold weather by selecting Timer
1 and Timer 2 together. Both Timer indicators will glow. The appliance will remain on standby at intervals
between the programmed finishing and starting times of each Timer. While the heater is operating during
programmed intervals the Timer indicator will flash.

–17 –
PRE-HEAT
The Pre-heat function will heat a room to the pre-set temperature by the programmed On Time.
1
This function operates automatically in conjunction with either of the Timers. When a Timer is selected,
the heater may operate anywhere within an hour prior to the programmed starting time of the Timer.
This function is called Pre-heat due to the way it operates. The room temperature is sensed one hour before
reaching the programmed time of either Timer.
The temperature differential at the time of sensing the room temperature, combined with the data from the
previous operation governs exactly how long before the programmed On time the micro-computer will operate
the heater and ignite the burner.
The following chart may help to improve understanding of the Pre-heat function.
Room temperature sensed
Earlier than usual ignition
Average starting time
Later than average ignition
Programmed time
6:00 6:30 7:00
Warmer than usual
Colder than usual
TIME ELAPSED FROM IGNITION TO PRESET TEMPERATURE Recorded by Micro Computer

–18 –
OVERRIDE FUNCTION
USING THE REMOTE CONTROL
This function is intended to be used to manually override the current operation of the heater, For
example; if the heater is in standby mode (i.e. between finishing time and starting time of a Timer), and
the Override button is selected, then the heater will begin to operate, and heat the room.
The heater will continue to operate on Override until the Override button is pressed again, or one of the
Timers takes over the operation of the appliance. This means that the Override mode will automatically
drop out if a programmed Starting time is reached. The appliance will then return to operating at times
programmed into the Timer(s).
1
To operate the Override simply press the Override
button. The Override indicator will flash.
Timer 1 Timer 2 Override
AM
PM
Set ・Room
Temp
・
Time
2
To manually deactivate the Override simply press the
Override button again. The Override indicator will go
out, and the heater will return to standby mode.
To manually operate
when Timer(s) are not
selected, simply press
the ON or OFF button.
To alter the
temperature at any time
while the heater is
operating, simply press
the “▲”or “▼”buttons.
Timer 1 Timer 2 Override
AM
PM
Set ・Room
Temp
・
Time
If the Timer(s) have been selected, and the heater is in standby mode, and the OFF button on the
Remote Control is pressed, the Timer(s) will be deactivated.
Remote Control will not turn heater ON if
Timer(s) have been selected.
To Turn ON or OFF To Change Temperature
ON
OFF

–19 –
CARING FOR YOUR NEW RHFE-308FTR
This appliance is controlled by a micro computer. If there is something wrong with the appliance then
it will stop, as it is protected by the following safety devices.
Ignition Safety Device Power Failure Safety Device
Burner Safety Device Power Surge Safety Device
Overheat Safety Device Fan Delay Safety Device
Your RHFE-308FTR requires very little maintenance,
simply clean the rear fan filter once a week and wipe
the outer case and louvre section with a damp cloth.
DO NOT USE SOLVENTS.
Solvents may melt or distort plastic parts.
Problem
Cause
Not Plugged In
Power Cut
(Initial Installation)
Air in gas pipe
Gas Filter Blocked
Missed Ignition
Flue terminal obstructed
Flue manifold not connected
Louvre obstructed
Air filter blocked
Gas Escape
On Timer is set
Child Lock set
Gas turned off at meter
Battery flat (remote control)
Remedy
No ON indicator
Burner doesn't ignite
Unusual combustion
Combustion stops during operation
Smell of gas
Noisy ignition
Takes too long to warm the room
Remote control doesn't work
Plug In
Re-ignite manually after
power is restored
Purge air
(Installer)
Service Call
Service Call
Clear obstruction
Service Call
Clear obstruction
Clean filter (weekly)
Service Call
Cancel On Timer
Cancel Child lock
Turn gas on
Replace battery

–20 –
PRE-SERVICE CHECK
Before asking for a service call please check the following points.
These points are part of the normal operation of the unit.
■At Ignition:
Heater does not operate.
Warm air does not flow when the burner lights.
Smoke or strange smells are produced on the
first trial light up after installation.
Sharp clicking noises at ignition, or when the
unit cuts down on the thermostat, or goes out.
Is the heater plugged in?
Have the fuses or breaker blown at the switch board?
Is there a power failure?
Is the air filter blocked?
Is anything blocking the outlet for the hot air?
Is the flue blocked?
Are Timers set? Clear Timers and operate again.
■During combustion:
Clucking noise when the thermostat operates.
Unit is not heating room.
Air filter is blocked or the louvres are blocked or
obstructed.
Heater will not re-ignite after overheating.
This is the sound of the solenoid gas valves opening and
closing.
■When the unit is turned off:
Convection fan continues to run after turning
OFF.
This is to remove the residual heat from the heat
exchanger, the fan will stop when the heater cools down.
■Other Points:
Steam is discharged from the flue terminal.
Unit cuts off without apparent reason.
Power Failure.
High efficiency appliances tend to discharge water
vapour on cold days, this is normal.
Check whether filters are blocked, dirty filters will cause
the heater to overheat.
Switch OFF, then ON again when power is restored to
re-set controls.
Is the air filter blocked?
Is the set temperature high enough?
Is the warm air outlet blocked by anything?
Are the doors and windows of the room closed?
Allow heater to cool, clean air filter, operate again.
Even after unit has cooled down the heater does not
ignite again. Repair is necessary.
Contact your local agent or Rinnai for a Service call.
The fan is started automatically after a short delay.
This is to allow the heat exchanger to warm up, helping
to avoid cold draughts.
This is caused by grease or oil and dust on the heat
exchanger and will stop after a short time.
This is simply expansion noise from the heat exchanger.
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