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HEMNVx & HEMSL Range Users, Installation & Servicing Instructions Doc Ref M103 issue 3.6 Mar 2020.
Important: The heater must NOT be
controlled by switching ON and OFF the
main electrical supply to it.
1) Standard Units
The ignition sequence commences each time the
external controls e.g. Time clock, room thermostat etc.
call for heat. The internal exhaust fan will run and, when
sufficient combustion airflow is proved by the air pressure
switch, the ignition spark will be generated, the main gas
valve opens and the burners light. The heater fan must
start a maximum of 2 minutes after the burners light.
When the external controls are satisfied the burners
will be turned off and the main fan is required to run on
sufficiently to dissipate the heat from the unit. If the
burners fail to light the control box will make another four
attempts at ignition.
2) High / Low & Modulating Units
When the burners are alight, the heat output will be
controlled either to high fire or low fire or, in the case of
modulating units, to any point between high and low fire;
depending on the requirements of the space being heated
and the external controls fitted.
3) Overheat Thermostat
This operates if high temperatures within the heater are
detected, the burners are turned off and a Red indicator
switch light on the front panel is illuminated. The fault
condition must be identified and rectified.
When the unit has cooled, push the Red indicator switch
inside the front panel to reset the limit thermostat
interlock relay, the red indicator light will go out and the
unit is operational again.
Note: The limit thermostat(s) can only be reset
once the unit has cooled down.
Unless the cause of the fault condition is
readily obvious, for example a power cut whilst
the heater was operating, a service engineer should be
contacted.
To maintain efficient, reliable and safe operation of the
heater it must serviced annually by a qualified person.
If the heater has not been left operational
proceed as follows.
The following preliminary checks should be made before
lighting the heater(s)
a) Ensure that the ELECTRICAL supply to the heater is
switched OFF.
b) Check that any warm air delivery outlets are open.
c) Check that the thermostat is set.
d) Check that the clock control is set to an ON period.
e) Check that any other controls are calling for heat.
1. Switch on the electrical supply at the isolator
2. If the Red Limit indicator lamp is illuminated, identify
the limit stat, remove the black cap and press the reset
button.
3. The startup sequence will commence. After a short
delay the burners will light and the green ‘ON’ indicator on
the front of the heater will be illuminated.
4. If the burners fail to light the control box will
automatically restart the ignition sequence. If after 5
attempts at ignition the burners have still failed to light
the control box will go to lockout and the Amber lockout
lamp on the front of the heater (or on the low level remote
reset, or MC200/MC300 if fitted) will be illuminated. To
restart the ignition sequence depress the reset button on
the low level reset for about 1-2 seconds.
WARNING: If it is not possible to light the
heater after several attempts, contact the
installer or local service company.
1) For Short Periods:
Turn the room thermostat to the OFF, or set to 'Summer
Mode'.
2) For Long Periods:
Complete step 1 above. Wait for 5 minutes and then turn
OFF the electrical supply at the isolator.