4. Note the setting of the old pressure switch.
5. Remove the screws fixing the air pressure switch and
remove switch.
6. Fit replacement in reverse order refitting the sensing
tube to the negative (- or L) tapping on the pressure
switch. Adjust setting to that of the old pressure switch.
2.7.6.7. Control Box
1. Unplug all the electrical connections.
2. Remove the four screws that secure the control box in
place.
3. Fit replacement in reverse order.
2.7.6.8. Centrifugal Fan/Motor
1. Disconnect the electrical connections to the centrifugal
fan section.
2. Remove the side panels of the section for access to the
fan and motor.
3. Fit replacements as appropriate and reassemble in
reverse order.
Note: If a 3ph motor is being replaced ensure that
the direction of rotation is correct. If it is not inter-
change any two of the three phases connected to
the motor.
2. Remove the electrical plug connections from the top of
the multifunctional control.
3. Release the flanged connections at the inlet and outlet
of the multifunctional control and remove the multifunc-
tional control.
4. Reconnect the new valve in the reverse order to that
above ensuring that the valve is correctly orientated.
Renew the sealing 'O' rings if necessary.
2.7.6.2. Burners
1. Remove the burner assembly as described in Section
2.7.2. Page 26
2. Remove the end plates of the burner assembly and the
central burner support plate.
3. Exchange burners as required and reassemble compo-
nents in reverse order.
4. Re-commission the appliance as described in Section
2.6. Page 22
2.7.6.3. Electrode Assemblies
1. Disconnect the electrode leads from the DMN control
box as appropriate.
2. Remove the screw securing the electrode assembly to
the burner assembly side plate and withdraw the assem-
bly.
3. Fit replacement and reassemble in reverse order.
Check that the spark gap is 2.5mm (See Fig. 9 page 27)
and the rectification electrode is 10 - 12mm forward of the
burner.
2.7.6.4. Fan/Limit Thermostat
Thermostat settings:-
Fan Off
Fan On
Limit
NVx 10-140 86°F/30
o
C 122°F/50
o
C 212°F/100°C
1. Squeeze the casing sides inward and pull casing
forward.
2. Remove the electrical connections from the thermostat.
3. Remove the screws securing the thermostat to the
bulkhead and withdraw.
4. Fit replacement thermostat in reverse order.
Important: In this application the brass link is removed.
Fig 10 Thermostat Fan / Limit – Honeywell L4064B
2.7.6.5. Exhaust Fan
1. Remove the four screws securing the flue outlet socket.
2. Disconnect the fan electrical connections from the main
terminal strip
3. Remove the screws securing the fan mounting box to
the exhaust header plate.
4. Remove fan assembly.
5. If needed, transfer the fan mounting box to the replace-
ment fan.
6. Fit replacement exhaust fan, using new gaskets and
silicon sealant as necessary, and reassemble in reverse
order.
2.7.6.6. Air Pressure Switch
1. Remove the two screws securing the cover and remove
cover.
2. Disconnect electrical connections.
3. Pull off the sensing tube from the air pressure switch.
2. Disconnect the spark and rectification leads from the
control box and remove the electrical plug connections
from the top of the gas control valve assembly.
3. Remove the burner heat shield, 3 screws.
4. Release the inlet connection flange from the gas valve
by removing the four screws.
5. If required remove the manifold by removing the four
screws securing it to the burner assembly.
6. Remove the two screws that secure the top of the
burner assembly to the bulkhead and lift out burner
assembly.
7. Using a stiff brush, not a wire brush, brush the burners
to dislodge accumulated deposits. Inspect the burners
both internally and externally to ensure that they are
clean. Examine the injectors and if damaged or deteriorat-
ed, replace with new ones of the correct size and marking.
If deemed necessary, clean the injectors. Do not broach
out with wire.
8. Reassemble the injectors, manifold and burners in
reverse order to that above.
2.7.3. Ignition and Rectification Elec-
trodes
Note: The ignition electrode is located at the
bottom of the burner assembly, the rectification
electrode is located at the top of the burner
assembly.
Inspect the electrodes, making sure that they are in a
sound and clean condition. In particular check that the
ignition electrode is clean and undamaged. Check that
the spark gap is 2.5mm and that the rectification probe is
10 - 12mm forward of the burner.
Fig 9 Ignition Electrode Spark Gap
2.7.4. Heat Exchanger
Whilst the main burner assembly is removed from the
unit, check that the primary sections that the burners fire
into are clean.
2.7.5 Main Fan Assembly
2.7.5.1. NVx/F & /CCF Models
1. Inspect the fan blades for any damage or excessive
buildup of deposits that could give rise to an imbalance.
Remove the assembly for cleaning as follows.
2. Slacken the cable gland on the heater casing through
which the fan electrical cable passes.
3. Disconnect the fan leads from the electrical terminals.
4. Withdraw cable through entry grommet.
5. Remove the fan and motor assembly complete by
removing the hexagon headed screws that secure the fan
to the rear panel.
6. Reassemble in reverse order.
2.7.5.2. Centrifugal Fan/Silencer Sec-
tion
1. Remove section side panel(s) and inspect the fan
blades for any damage or excessive buildup of deposits
that could give rise to an imbalance. Remove the assem-
bly for cleaning as follows.
2. Slacken the cable gland on the casing through which
the fan electrical cable passes.
3. Disconnect the fan leads from the electrical terminals in
the contactor enclosure.
4. Withdraw cable through entry grommet.
5. Remove the complete fan assembly by removing the
fixings securing the fan to the base rails.
6. Reassemble in reverse order.
2.7.6. Replacement of Faulty Compo-
nents
2.7.6.1 Multifunctional Control
1. If there is movement available on the incoming gas pipe
work e.g. a flexible connection has been used go to step
2 otherwise remove the burner assembly as previously
described in Section 2.6.2. Page 28
WARNING:
Always switch off and disconnect
electricity supply and close the gas service valve
before carrying out any servicing work or
replacement of failed components.
NOTE: If a suspended air heater is to be
serviced do not lean ladders against the heater.
Ensure that an access tower or equivalent is
used.
NOTE: The access door to the controls section
may be removed to improve access. Open the
door to 90°, remove the earth cable at the
bottom, and then lift the door vertically upwards
to disengage the hinge plates. Refit in reverse
order. Ensure that the earth cable is refitted.
NOTE: Whenever the electrical supply to the
heater is interrupted and subsequently restored
it will be necessary to reset the limit thermostat
interlock relay by pressing the reset switch on
the front panel.
2.7.1. General
Full maintenance should be undertaken not less than
once per year by a qualified person. After any servicing
work has been complete, or any component replaced,
the air heater(s) must be fully commissioned and tested
for soundness as described in Section 2.6 Page 24
2.7.2. Main Burner Assembly Removal
1. Ensure that the gas service valve is turned OFF and
then unscrew the union nut situated immediately down-
stream of it.
2.7 Servicing
10.0
10.0
9.0
9.0
8.0
8.0
7.0
6.0
6.0
5.0
5.0
4.0
4.0
3.0
3.5
4.0
3.0
2.0
1.0
0.3
2.6.6.1. Standard Units
This is set for the required heat input before despatch. In
the case of Hi/Lo and Modulating units both high and low
pressures are set. Pressures should be checked in the
following manner.
2.6.6.1.1. Standard Units
1. Set external controls to ensure that the main burner is
off.
Open the side access door. Connect a pressure gauge to
the burner pressure test point on the multifunctional
control.
2. Set external controls so as to turn on the main burner.
Compare the measured burner gas pressure to that
stated on the data plate. If necessary adjust the burner
gas pressure by turning the regulator screw anticlockwise
to decrease the pressure, or clockwise to increase the
pressure.
3. In addition it is advisable to check the gas rate using the
gas meter dial pointer. Ensure that no other appliances
supplied through the meter are in operation.
4. If required, after checking or setting the burner pres-
sures, the CO2 content in the flue gases can be checked
by sampling in the first section of flue fitted to the flue
outlet of the unit. Nominal CO2 values are given for guid-
ance in the Table at the bottom of the previous page.
5. Turn off the main burner and disconnect the pressure
gauge and replace the sealing screw. Turn on the main
burner as above and test for gas soundness around pres-
sure test joint using a leak detection fluid e.g. soap
solution.
Governor adjustment screw under cover cap (Honeywell
VK4105A1001B)
Fitted to the NVx 10 to 50
Governor adjustment screw under cover cap
(Honeywell VR4605AB1027)
Fitted to the NVx 60, 75, 90 and 90S
Governor adjustment screw under cover cap (Honeywell
VK425AB1007)
Fitted to the NVx 120 and 140
2.6.6.1.2. High/Lo Regulator
1. Set external controls to ensure the main burner is off.
Open the side access panel. Connect a pressure gauge to
the burner pressure test point on the multifunctional
control.
2. Set external controls to turn on the main burner and
maintain high fire. Compare the measured burner gas
pressure to that stated on the data plate. In addition it
is advisable to check the gas rate using the gas meter dial
pointer ensuring that no other appliances supplied
through the meter are in operation.
3. Repeat 2 above with external controls set to maintain
low fire.
4. If it is necessary to adjust either the high fire or low fire
pressures proceed as follows after levering off the plastic
cover from the Hi/Lo regulator.
Note: High fire setting must be adjusted first after
which the low fire setting can be set. Any adjust-
ment of the high fire setting alters the minimum
setting.
Maximum Setting
With the controls set to high fire use an adjustable or 8mm
spanner to turn the adjustment screw for high fire pres-
sure, clockwise to increase and counter-clockwise to
decrease, until the required pressure is obtained. Turn the
burner On and OFF several times to check the pressure
setting and then turn off.
Minimum Setting
Disconnect electrical connection of high/low regulator and
turn burners back on and wait until the burner pressure
has stabilized. Use a screwdriver to turn the slotted
adjustment screw for low fire pressure, clockwise to
increase and counter-clockwise to decrease, until the
required pressure is obtained. Reconnect high/low regu-
lator and check high fire pressure. Repeat both steps if
necessary and then replace cover cap.
5. Turn off the main burner, disconnect the pressure
gauge and replace the sealing screw. Turn on the main
burner and test for gas soundness around pressure test
joint using a leak detection fluid. Replace access panel.
2.6.6.1.3. Modulating Regulator
1. Set external controls to ensure that the main burner is
off. Open the side access panel. Connect a pressure
gauge to the burner pressure test point on the multifunc-
tional control.
2. Set external controls so as to turn on the main burner
and maintain high fire. Compare the measured burner gas
pressure to that stated on the data plate. In addition it is
advisable to check the gas rate using the gas meter dial
pointer ensuring that no other appliances supplied
through the meter are in operation.
3. Repeat 2 above with external controls set to maintain
low fire.
4. If it is necessary to adjust either the high fire or low fire
pressures proceed as follows after removing the plastic
cover from the Modulating regulator.
Note: Minimum fire setting must be adjusted first
after which the high fire setting can be set. Any
adjustment of the minimum fire setting alters the
maximum setting.
Minimum Setting
Disconnect electrical connection of modulating regulator
and turn burners back on and wait until the burner pres-
sure has stabilized. Turn 9mm adjustment nut for low fire
pressure clockwise to increase and counter-clockwise to
decrease until the required pressure is obtained. Recon-
nect modulating regulator and check high fire pressure,
readjust if necessary.
Maximum Setting
Disconnect electrical connection of modulating regulator
and turn burners back on and wait until the burner pres-
sure has stabilized. Push shaft gently downwards to the
maximum adjustment screw and hold there. Turn 7mm
adjustment nut for high fire pressure, clockwise to
increase and counter-clockwise to decrease, until the
required pressure is obtained. Release shaft. Repeat both
settings if necessary and then replace cover cap.
5. Turn off the main burner, disconnect the pressure
gauge and replace the sealing screw. Turn on the main
burner and test for gas soundness around pressure test
joint using a leak detection fluid. Replace access panel.
Page 26 NVX Range Users, Instructions & Service Instructions Issue 5.5 August 2015
2.6.6.2. Modulating Interface Board
Fig 8 Modulating Interface Board
The MIB interfaces between a 0-10VDC control signal
and the modulating regulator. The following are applicable
to this application.
1. The setting of the slide switches 1 & 2 should both be
to OFF.
2. Potentiometer P1 (Default setting 100%)
The control current of the V7335A is controlled by P1,
varying between 50% and 100% of the input signal.
E.g.
-When P1 is set at 100% (fully clockwise) maximum
power (165mA @ 22VDC) is provided to the modulation
coil with a 10VDC input control signal.
-When P1 is set at 50% (fully anticlockwise) maximum
power (165mA @ 22VDC) is provided to the modulation
coil with a 5VDC input control signal.
3. Potentiometer P2
Controls the minimum drop-out voltage between 0% and
40% E.g.
- When P2 is set at 0% the drop-out voltage with an input
control signal of 0-10V-DC is 0.3V-DC.
- When P2 is set at 40% the drop-out voltage with an input
control signal of 0-10V-DC is 4.0V-DC.
4. Potentiometer P3 (Default setting 100%)
Controls the maximum hold-in voltage. Its proportional
value is added to the P2 setting E.g.
- When P2 is set at 0% and P3 is set at 5%, the hold-in
voltage of the burner relay is adjustable between 5% and
100% of the input control signal. If the input control signal
is set at 0-10V-DC the hold-in voltage of the relay is
0.5V-DC.
- When P2 is set at 40% and P3 is set at 5%, the hold-in
voltage of the burner relay is adjustable between 45% and
100% of the input control signal. If the input control signal
is set at 0-10V-DC the hold-in voltage of the relay is
4.5V-DC.
The following table shows the relationship between P2
and P3 settings.
2.6.6.2. Flame Current
1. To measure the flame current connect a multimeter
capable of measuring micro amps as shown in the follow-
ing diagram.
2. Minimum current reading is 0.5mA and normal value
should be 1.5mA or higher.
Fig 8 Flame Current Measurement
2.6.6.3. Air Heater Controls
1. Close the gas service tap and ensure that the gas valve
is heard to close within 1 second and that the lockout light
is illuminated. Note that the heater may attempt five re-ig-
nitions before going to lockout. Open the gas service tap
and reset the unit from lockout.
2. Check that the room thermostat and all automatic
controls are operating satisfactorily.
2.6.7. Fan/Limit Thermostat
Thermostat settings:-
Fan Off
Fan On
Limit
NVx 10-140 86°F/30
o
C 122°F/50
o
C 212°F/100°C
Note: NVx 10 to NVx 75 units have one fan/limit
thermostat whereas NVx 90 to NVx 140 units
have two. The second thermostat is at the oppo-
site end of the heater to the burner/controls end.
The fan circuits are wired in parallel (either
thermostat will turn on the fan) and the limit
thermostats are wired in series (either thermostat
will shut down the burner)
2.6.8. Handing over the Air Heater
Hand these instructions to the user or purchaser for reten-
tion and instruct in the efficient and safe operation of the
air heater and associated controls. Adjust the automatic
controls to those values required by the User.
Finally, advise the user or purchaser that, for continued
efficient and safe operation of the air heater, it is important
that servicing is carried out annually.
In the event that the premises are not yet occupied turn
off the gas and electricity supplies and leave instructional
literature adjacent to gas meter.
P2%
0
10
20
30
40
0.5
2.5
1.5
4.5
1.0
2.0
5.0
2.0
3.0
6.0
3.0
4.0
7.0
4.0
5.0
8.0
5.0
6.0
9.0
6.0
7.0
10.0
7.0
8.0
8.0
9.0
Drop Out
5
10
20
30
40
50
60
70
80
P3%
90
100
9.0
10.0
10.0
Hold-in Voltage
Volts
7.0