Apa calda intermitenta sau centrala (termica pe gaz Viessman Vitodens 050) nu mai incalzeste ACM

We have a problem with a gas boiler without error, the problem is that the domestic hot water no longer heats to the set temperature and fluctuates, we practically have no hot water. The problem is reported on a Viessmann Vitodens 050 boiler, the same boiler in two different places but the problem can occur with any boiler, obviously, each manufacturer has its own construction particularities. The costs were minimal, in the first case we bought the cleaning agent and in the second we had no costs for materials. We also had other interventions on this boiler model, here is the clip: Gas boiler loses pressure - diagnosis and repair (Viessmann Vitodes 050)    • Centrala termica pe gaz pierde presiune - ...