You can hire from most hire shops. Diy is not as hard as it looks but kep in mind, when hard water is heated, calcium and magnesium contained in the water can build up a limescale in the central heating system, especially in boiler's heat exchanger. This creates an insulating layer, reducing heat transfer to the water and reducing efficiency of the boiler. A 1 mm layer of limescale will cause a 7% increase in energy input to the boiler to meet the same heat demand, so more gas is burned and fuel bills are much higher. Limescale can also restrict or block water passageway in the central heating system (especially in boiler heat exchanger) affecting water flow rate and reducing water temperature. That is not o straight forward to remove.
