Hi OP - Delayed welcome, as it looked like a low number post
Your coach should be able to handle the cold pretty dang good. So yes you either have some of the controls not set properly, and or a functionality problem is need of repair.
I would double check you manuals, to be sure you have all of the settings set properly to support maximum heat generation. With most Aqua/HdroHots that I know of, that means setting on both Electric (The single and or double (Depending upon model.) electric heating elements heat the tank of boiler fluid that is used to circulation to the heat registries within the coach. Our coach has a HydroHot with a 'single' electric heating element. It does a good job of providing hot water for washing dishes, shaving, and even a few navy showers. It will also maintain the heat in the coach down to around the high 30's to low 40's. Especially if only heating one zone of the coach. Where as a 'double' electric heating element equipped unit - will cover almost 65-75% of the water and coach heating demands that the propane/diesel fuel burner heating unit will.)
OK, so some AquaHot's are run on diesel, probably the bulk of them. But some are also run on propane. In the control area, you should have in addition to the Electric option, either a Diesel/Gas/Fuel option (My coach says Diesel.)
When hooked up to 50A or 30A shore power, I suggest turning them both on. That way the electric heating element(s) will take care of the much of your heating demands, and then the Diesel/Gas/Fuel option of firing up the burner portion of your AquaHot will kick in only when needed.
Suggest that you turn on one zone of your heating, set it up to 90, then check that the registers (Where the heat comes into the coach. This basically a mini radiator that pulls the hear out of the circulating fluid, and then fan fed out into the coach.) are putting out heat. If you do not detect heat air flow, still feel up close to the register, and see if you can feel any heat at all. (If you feel heat, then you know the circulation system is delivering hot boiler fluid to that register, and the fan may have gone out.) Check each register in that zone. Note any with problems, then change over to the next heating zone in the coach, until you have checked all registers.
This way you can point out to a service tech where you feel you are having heating problems, if any. They can then check or if you want to you can too, the various circulation pumps within the AquaHot bay. As mentioned already, a little finesse with a well paced 'tap' to the circulation pumps, can sometimes shake them awake
Once you get all things working, I recommend you add a regular exercise maintenance to the system. (Even when not using the coach or not needing say heat and or cold, I do run all systems once every 6-8 weeks. The old 'use it or lose it' saying. I'm lucky as we do not need to winterize. So when not in use, I go and get the coach every 6-8 weeks, and go drive it for about an hour. Get the tires up to temperatures. Run the Over The Road heater and AC. Run the Generator the full time I'm driving. Run the roof AC's, run the Heat Pumps. Before leaving, I fire up the Diesel/Propane/Fuel option of the HydroHot. Let it run long enough for the diesel to get the boiler fluid up to temperatures. I run the heater in all zones. This is sort of a pre check flight, before the drive. I run the generator at this time too, as I want to get as much time as possible on the generator, while doing this exercise (Do keep at least a half load on the generator at all times during this exercise. Even if you don't really need to. Even just running the AC units on High Fan only, will put some load on the generator.)
And my final tip to you. When posting for help on a thread, try to provide as much info as you can. For example on this post. Taking the time to post the model of the AquaHot, would have allowed some of the veteran's on this forum to provide you with more finite info.
Ok, not my final tip
! If you know the weather forecast is showing a freeze ahead. Top off your water tank, put your hose away for overnight (Both water and sewage.). If in extreme cold, some coaches need to have some of their inside cabinet doors open to allow some inside coach heat to the water lines running in the outside walls. (Suspect your coach will not require this until way down low temperatures hit.)
Enjoy yourself, and best,