To permit partial load operation, a control arrangement is provided to effect, in dependence upon an operating load of the boiler, {TAIL ~ control} of at least one of the flow rate of the combustion air into the boiler, and {HEAD ~ the operating pressure} in the combustion chamber of the boiler 
To permit partial load operation , a control arrangement is provided to effect , in dependence upon an operating load of the boiler , { TAIL ~ control } of at least one of the flow rate of the combustion air into the boiler , and { HEAD ~ the operating pressure } in the combustion chamber of the boiler
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