Even if the water is *very* hard it only holds so much mineral. The washer used new water continuously but the heating system is a closed system. The only time new minerals are added is when the water is changed. I'm betting on air or something mechanical is blocking.
Start at the boiler and follow the pipe to see where it gets cold. Do you have several "loops" in the system? follow each "loop". The circulator is probably pumping water into the boiler so the other pipe would be the hot coming out of the boiler. Following that pipe, see how many times it branches off and that's how many "loops" you have.
Multiple thermostats? If so then you have "zones" and some sort of solenoids or valves to operate the "zones" independently. That would be a potential source of trouble.
If you shut the boiler down and put a hose on the drain, then open the makeup valve that adds water to the system and open the drain to get a good flow it should flush out sediment and more importantly a good flow will push out large pockets of air. Then shut the drain valve and let the system come up to the cold pressure marked on the boiler gage. It will probably be graduated in feet. At cold pressure it should be more feet on the gage than the highest point in the system is above the boiler, in feet.
Fire the boiler and when the temperature comes up the water will precipitate air which will have to be bled. The best way is to have someone stand by on the makeup valve and don't let the pressure drop while you follow the pipes and crack every bleeder to release the air. It *WILL* have to be done more than once.
You should be able to make the room hot with no insulation and the windows leaking, it's just more expensive.
You didn't mention what kind of heaters you have but you said "wall panels" so I would assume you have baseboard heat of either cast iron or more likelyn finned pipe surrounded by a sheet metal enclosure. Look inside the enclosure, particularly any place the pipe turns down, for air bleeders.
No, your insurance doesn't cover unless you got some kind of warranty when you bought the house.
Sleep with a hot woman or several dogs.
