Confusing when it happens, but if you randomly touch a radiator and discover it is on during the summer, you are bound to question why? Well, your radiators being on may be a sign of an issue within your plumbing system. Radiators work using a thermometer, if the temperature within the room goes below a certain level that you choose, the radiators will turn on to warm it up to this level. So, your radiators being on in the summer either means your room is below your ideal temperature, or there is an issue within your heating system causing it to believe the room is cooler than it is. Ideally, you want to call out a professional plumber to take a look and solve the issue. If they discover there is no issue, the best idea for you will be to turn your radiators completely off at the boiler until you need to use them in the cooler months.