The bar pressure keeps going into the red. I regularly drain off excess water. It has been proven that water is not entering via the double filling valves. How else can the system fill itself and if it is a faulty part what costs are involved to replace same.
You could simply have trapped air in the system. This will cause a high pressure at the gauge. Open the vent at your highest radiator checking for trapped air.
When you state that water is not entering via the double filling valves do you mean it is not possible that the valves are defective allowing water to pass? Remember if a valve is defective it can still indicate that it is closed but it is passing water. Although unlikely you could also have a faulty pressure gauge.
Try shutting the boiler down completely and waiting until the water temperature has equalised. Drain any water off such that your boiler circuit pressure is less than the mains water pressure on the other side of your filling valves. Check the pressure gauge over a period of time to see if it is increasing. If it is then you have defective filling valves that are passing water.