I have a Navien CR210 and Navien HBC 100 closed loop heat box setup. The domestic side is a dual head shower and sink, the floor heat side is a 150sq/ft room and the seating in the shower (we don't heat this).
I believe this was installed around 2009, and I bought this house in 2017.
This is coming up on our second winter in the house. Last year, we had zero issues with the heat side, and intermittent issues with the DHW. I descaled the system (we actually have fairly soft water in our municipality), and also found that the air sensor on the CR210 unit needs to have the inner membrane re-seated from time to time. It's annoying, but not the end of the world. The shower also doesn't like to run for more than 10 mins without going into a fault mode.(no problem for me, but my wife generally takes her time)
The current issue - The floor heat isn't working. When I turn on the thermostat, the heatbox turns on, I see the flow icon for the water heater controller come on, but we get no heat to the floor. If I turn on a DHW tap, the heatbox turns off, and I get hot water to the tap. When I turn the tap off, the heatbox comes back on, and requests heat. It sounds like everything is cycling properly.
I know the water is circulating on one side of the heatbox because the lines get hot, and the heat exchanger is definitely hot. The lines on the closed loop side are room temp.
I drained the open side and looked at the DHW switch. Not much to it, and I am not sure how it works, but no scale or anything like that. I also noticed the pressure gauge shows no pressure on the closed side. There is no mention in the manual of what I should expect there.
The manual for this system is pretty vague. I am not sure how to go about draining and refilling the closed side. Is it regular water? glycol? do I need a hose to refill or will it take water from the domestic side? etc.. so I have not been able to inspect, or test the pump on closed loop side.
I don't really have the money to replace the system with anything better, and I would rather not pay a plumber to come in. I am an instrumentation tech, and I have experience doing maintenance on water cooling systems for large radars etc.
Does anyone have experience with this system that can offer some insight or advice? It is starting to get cold, so I either need to fix it, or drain it before we get freezing temperatures.