Skin boils on the lower legs?

My father is a 77-year-old heart patient. For the past 3 months he is getting boils (water filled) on his lower legs. They usually increase in size for 2-3 days then bursts and becoming a wound. As long as the first boil heals another one is appearing . This has been going on for the past 3 months. Somebody advised that it may be happen due to poor blood circulation in the legs. To clarify this we got color Doppler of the lower legs arterial flow of both lower legs but that was normal. Can anybody explain why the boils (I don't even know if they are boils or not) are forming on the lower legs again and again. Is this a dermatological condition or an issue related to blood circulation? My dad has CAD with left ventricular dysfunction is this anything to do with the boils? Can you suggest the ways to properly diagnose this condition and find a treatment? Any other tests to carry. He is not a diabetic. His recent creatinine level was 1.5.