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HEMNVx & HEMSL Range Users, Installation & Servicing Instructions Doc Ref M103 issue 3.6 Mar 2020.
To commence servicing, firstly open the air handler
compartment door.
1. Ensure that the gas service valve is turned OFF
and then unscrew the union nut situated immediately
downstream of it.
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
deteriorated, replace with new ones of the correct size
and marking. If deemed necessary, clean the injectors. Do
not broach out with wire.
8. Inspect the heat exchanger tubes (See section 2.7.8)
9. Reassemble the injectors, manifold and burners in
reverse order to that above.
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.
2.5mm
Ignition
Electrode Spark
Gap
Whilst the main burner assembly is removed from the
unit, check that the primary sections that the burners fire
into are clean.
1. Disconnect the fan electrical connections from the
main terminal strip and the air pressure sensing tube
from the fan.
2. Loosen the six screws holding the main control panel,
lift the control panel up and clear of the fixing position
(taking care not to snag the wiring) and move to one side.
3. Remove the screws holding the fan box assembly to
the exhaust header and remove the assembly.
4. Clean impeller by brushing with a stiff brush
5. Re-assemble using a new sealing gasket to the fan
mounting box. Use silicon sealant around the joints.
1. Disconnect the fan electrical connections from the
main terminal strip and the air pressure sensing tube
from the fan.
2. Loosen the six screws holding the main control panel,
lift the control panel up and clear of the fixing position
(taking care not to snag the wiring) and move to one side.
3. Whilst supporting the fan motor remove the three
screws securing the fan motor mounting plate to the fan
casing and carefully withdraw the motor, mounting plate
and impeller.
4. Clean impeller by brushing with a stiff brush
5. Reassemble in reverse order.
6. Re-commission the unit