This is a write up about a three way valve controller I decided to build. Project started when we had a Nibe air to water heat pump installed. We left our old oil based system more or less intact, in case it was needed when the temperature got too low for the Nibe. We also made a connection from the oil boiler to the Nibe so we could use it as a external heating system. Nibe has a maximum input temperature of 65 degrees Celsius. So we needed a controller to control the water temperature. First we installed a commercial solution, but for some reason it didn’t close the valve when the maximum temperature of 55 was reached. One solution would of been reverse engineer and fix the controller, but wheres the fun in that. So I decided to build my own.