In doing research for a future Entegra Coach purchase, kits are available for the Aqua Hot units that contain the necessary new nozzle, filter and seals for the yearly maintenance. Also I believe I read where the units have a tool used to the igniter probes.
Some complain about access to perform their own servicing on their Aqua Hot equipped coaches. So depending on the coach layout you may be working on the AH from the compartment next to where it lives via an access panel
When I lived in Alaska I installed a diesel fired Beckett burner, diesel tank and plumbed the 3 story house for Hydronic heat, later adding a hot water heater that was an additional zone from the boiler for domestic hot water. Sure did beat the electric baseboard heat the house was built with.
Couple decades ago my X wife and I visited her parents on the shore of Lake Michigan. They had a 2 story rental unit that had radiant ceiling heat. If you sat in the main living area (1st floor) you were cold. To warm up you stood up where all the heat was living. Now that was a joke of a heating system. 80 degs at the ceiling and 65 degs at the floor.