Chappee stove burning problems

I am wondering if anyone has info on Chappee hand fed boilers. My business partner has one and it is set up to burn coal although he is a wood burner.( I am converting him) The problem is finding parts for it and it is difficult to regulate. He is trying to find the aquastat that was on it previously to make it more responsive to temp swings.
Today while I was there he showed me what it is doing. It had a nice fire going and the water temp was just over 180. He opened the door and put in enough coal(nut) to cover the burning bed. It immediately started to ignite and the blue flames were dancing on the top. Within 5 minutes his water temp dropped to 170 and continued down to 155 even though there was no call from the house. I have observed this in my flue temps but not in the water temps. It took 20 minutes to start to regain the heat in the water. And because someone will ask, no he does not have a baro in the flue. I am convincing him to install one but the lack of one does not explain loosing 30 degrees of temp in at least 30 gallons of water. How can it cool the water down? I told him the info in the Harman post about how to add coal to a hand fed boiler. We shook down the grates gently until several nuggets fell through. I put my hand over the draft door held wide open and I could feel a good draft. There must be at least a foot or 16 inches of burning coal over the grates. It seems to be operating well but at times it just goes out or does not seem to produce any heat for the fire in it.(baro)

i had a chappee hand fired coal boiler about 25 years ago.
any honeywell aqastat should work that will give you the temp spread that you are looking for, i think a honeywell came with it.
in the winter the heat in your house travels through the walls, windows ect towards the cold which is out side, the cold does not travel towards the heat.
i believe that it is a law of physics if i remember correct.
the coal that you are putting in the boiler is a lot colder than the coal that is burning under it.
the heat from the burning coal travels towards and into the cold unburnt coal, the cold coal also is in contact with the metal water jacket,
the heat from the water in your boiler is also going through the metal water jacket into the cold coal. after the temperature equalizes and the cold coal can no longer absorb any more heat it will ignite because it is at its flash point for ignition. then all the coal will be hoter than the steel and water and the heat will reverse and travel into the metal walls of the boiler then into the colder water.
this roughly how it works, if i am wrong someone will correct me, that has more hand burning knowledge than me.
after you shake the coal down you want to see quite a few embers fall not just a few, then put as much air flow from the bottom of the grates up through the coal that you can. you also want some air over the top of the coal to burn off any coal gas it is giving off. after 5-10 minutes when you open the top door it should be as hot as standing at the entrance to hell. try only putting in half the coal needed and wait 5 more minutes with the high air flow through the bottom of the coal bed, then put in the rest of your coal. your temp swings will flatten out.
if you don't put the air right to it from under the grates after you shake it, but just put the coal in after you shake it you will see these large temp swings, some times the new coal will put the fire out,
if you adding more new coal than what is burning.

eskimo