We have recently moved to a house with this boiler, regularly serviced but believed to be about 20 years old. Problem is with the temp of the hot water & heating. The control thermostat dial is set at the lowest (the smallest dot) and yet the water is boiling?. Not at all familiar with oil and no manual, but we have used 500 litres in 3 months, this is with very little central heating on and this seems very high usage. We just want the boiler to run at a lower temperature, can this be adjusted as the thermostat can not go down any lower?. Thanks.