Are the radiators not functioning, or getting hot just partially? Maybe it is time to refill your Central Heating System. This sounds difficult, but with the following steps you can do it easily yourself. First, you have to check the pressure gauge. If the pressure is below 1, it is time to refill the system.
How to refill the Central Heating System? Please check the following instructions:
You will need:
If you need more instruction, please check this video of the Energiewacht (in Dutch)
After refilling the Central Heating System you have to vent all the radiators.