Lots of people love to clean siding with a power washer. But there are a few drawbacks I have learned. First, if your siding is just dirty and you just want to change color p/w is just fine. However, depending on the condition of your siding you need to exercise restrain. First, if there is dryrot the p/w will significantly reduce the quality of the boards by blasting out the rot leaving holes that then need to be properly treated before painting. Second, if there are cracks that high powere water will go under the siding and cause problems either in the house or outside as the water tries to evaporate. So, power washing may, or may not, be the answer for you. Hire someone in the know to give you an honest opinion. If you are going to spend the money to do the job do it right and it will last 10 years.