You can clean the cyclone by first removing the exhaust pipe, then unbolt the flange where the pipe connects to the boiler, that will give you access to the cyclone. Clean the cyclone with a wire brush. Then make sure ash is cleared from the funnel at the bottom of the cyclone. That hole can be accessed from the bottom as well.
Leave the cyclone disassembled.
Next, remove the fan assembly which will give you access to the swirl chamber. Clean inner and outer sections of the heat exchanger with a long handled wire brush and a shop vac.
Make sure you clear the hole between the cyclone and the heat exchanger. This is best done by running a brush through the hole from the cyclone side. Check to see if anything fell into the heat exchanger from cleaning that hole. If so, remove the debris.
Reassemble the boiler. It is best to install a new gasket at the cyclone flange.
Also, the Coal Gun should be operated at a high enough temperature to have 150 degree return water. That should eliminate condensation. Thus, your operating temperature becomes relative to the amount of return water in your zones. I would generally suggest 180 as the best minimum operating temperature.