ALso, what is your exhaust? Direct Vent or standard chimney?
The adjustment screw can be backed out about 2-4 turns depending on how low you want it to idle.
Are you using a standard Thermostat (dial or digital) or a Coaltrol?
If you can't hear it clicking on/off when you turn up the standard thermostat, then something with the relay box or thermostat is not working.
Yes, it might need cleaned, if you are getting a good burn on the grates, but low, something is not making it kick up to full burn.
The grates can be removed and cleaned under them, many small fines fall thru, you could remove the combustion blower from the back and vacuum it out with a small tube in and under the grates without removing
Heres a write up I did a while back. hope it helps.! I'm going on my 12th year with my keystoker. as long you clean it out faithfully in the spring and oil everything. it shouldn't give you too many problems.Cleaning & Sealing Burn Grate