We install and service Triangle Tube Excellence boiler here in St. Paul, MN and find them like any other "Combi" boiler/water heater...of limited use. That is, one must carefully size any combi-heating appliance to cover both the space heating load and the domestic hot water load. Since these separate loads are almost always imbalanced, the heating greater than the water, or peak demand for DHW exceeds the design load for heating, it makes specifying the Excellence a little tricky. They can be great for a couple of showers but the only way to fill a large tub--more than 60 gallons--is with standing water sized to the load. Say the Triangle Tube 110 with a 60 gallon Smart Tank.
The reason you only experience the cold water in the winter is the domestic water you start with being colder in winter and it takes more heat to raise the temperature to the same level. This is a symptom of designing to close to the spec. The Excellence has a small storage tank on-board and will outperform any "tankless" water heater with a similar output since a little storage goes a long way. Like a tankless the Excellence Combi Boiler will keep up with a typical shower if the flow is restricted so the boiler can keep up--something tankless water heaters do automatically.
Performance, and reliability will suffer if the boiler is not serviced regularly by qualified technicians.