I have a boiler with the type ``Ideal Sprint Rapide 90NF Combination Boiler`` in my rented flat. The hot water is fine. However recently I try to use the central heating, I find overheating will come up within 20 minutes, although the radiators become hot. In this case, hot water and central heating will never come again, although the radiators become cold. I have to reset, the central heating will work, but overheat will come again within 20 minutes. I think there is something wrong. Could you please give me some advices? thanks