Hi just to give you a heads up, i was commissioning 2 x oil boilers both with riello rdb pumps, when using vacuum gauge on vacuum port on the pump i had a oil leak after putting the allen key screw back in. Here is the problem, the rubber seal which is green is slightly too big and while screwing out the vacuum port screw the seal stays in the port and can get nipped. So if this happens try and recover the green O ring undamaged before you put in your vacuum gauge. It will save you an oil leak. Hope this helps.