Koker 160 Fire Bed Too Small

Hi All, I have a koker 160 with direct vent and thermostat. This is my second season using the koker, thought I had it figured out but am having an issue with the fire bed. Last night when I got home from work the back bedroom, which is furthest run from the stoker was only at 66 degrees, the room is normally 70 - 72 degrees. When I checked the stoker, when calling for heat, the fire bed was about only 1/2 of what is normally is. So it is not putting out like it was. Not sure why. Typically I have about 1" if ash before it falls into the can. Now there is about 3- 4 inches of ash. I checked the draft and it was at -0.02 as specified. Checked the pushed bar and nylon cam and that seems to be working fine. I did try to increase the coal feed a turn at a time for 2 turns but it didn't seem to make a difference and I wasn't sure about doing this since it has been working overtime this winter with no other issues. I did 2 clean outs this year, just the direct vent and stove pipe. I haven't cleaned under the grates since the end of last last year. The last clean out was February 9th but it has been working hard since then. I also did just get 4 ton of coal, from south Tamaqua, which visually looks good and was burning fine. I am planning on shutting down after work today and give it another cleaning for now. The way this winter has been going I really don't want to shut it off for the season yet and when I do I want to make sure it is good to go next season. Any advice or comments would be appreciated. Thanks

I'm pretty sure you need to remove the combustion motor and vacuum out the cavity under the grate. You should also run an appropriately sized drill bit through all the holes, by hand, to make sure they're open completely.
As the fines in your coal work their way down through the holes, they get blown forward and begin to collect, blocking the airflow up through the grate at the front. If you have a lot of fines in your coal, this will happen sooner rather than later.
My best guess.
Good luck,
-Len

If your stoker mechanism looks good, maybe empty your coal hopper and make sure you don't have a blockage and make sure your pusher bar is moving the required full length it needs to (possibly getting bound up by excessive fines??). Maybe your air holes are plugged up on the coal bed grate, towards the end of it.

I would suggest shutting it down for a good cleaning. Clear all the holes in the grate w/ drill bit and vacuum out under neath them by taking the combustion blower off and attaching a long tube to a vacuum hose. That would eliminate that possible problem, then take a look at the other previously mentioned ideas. This is also a good time to make sure your chimney/stove pipe is nice and clear (yes I know you said your draft is good, but it never hurts to check things out).

Added : sorry for the duplication. Coalen added his comment before I hit submit, so I didn't know he had commented.

Thanks Rob and Len. I will be doing a good cleaning tonight. I appreciate the comments. I did notice that the new coal does seem to be a bit, I would call it dusty. Maybe that and the fact that it has been working hard all winter contributed to the build up of fines under the grate.