STOP STOP STOP !!!!.
The glass is getting dirty for one of two reasons assuming you are burning wood.
The most likely is that you are using primary air UNDER the fire, wood burns from the top down, once the fire is established the ONLY air you want entering the stove is via the secondary air supply which comes down the inside of the glass. On the Herald 8 the primary air supply are the two slides in the lower part of the doors, the secondary air supply is the slide above the center of the two doors.
Set your new fire on a bed of old ash, that protects the grate and makes it last longer. Start the fire with primary and secondary air fully open and even the doors slightly open for a few minutes. Once the sticks are going put smallish bits of wood on and close the doors, once they are going then on with full size logs and close the primary air supply slides, the fire is now managed with the secondary air supply slide above the door.
The other reason for dirty glass is crerosote on the glass, always load your stove with the cut ends facing the side of your stove, thats where gases that contain the crerosote come out. If the cut face is just inside the glass the crerosote will get onto the glass before the fire can ignite it, again the fire will burn it off but it will take some time.
Your fire when managed properly will burn off crap on the inside of the glass after an hour or two. You will get a small build up of smoke right along the bottom inch or so of the glass, this is because by the time the secondary air supply which forms a curtain between the glass and the fire gets down to the bottom it has all been pulled into the fire.
A squirt with smoke remover from your local stove shop will shift it, Mr Muscle kitchin will also do an acceptable job.
If you are burning smokeless fuel then leave the secondary open all the while and control using primary air supply, keep the grate clearish of ash when refulling. Smokeless fuel burns from the bottom up hence the different settings.
I am surprised that your stove retailer did not either send you detailed instructions in addition to those supplied by the manufacturer or come and give you a hands on driving lesson. Maybe you bought it online.
A happy xmas to you all.
A