Here, we'll go through the most frequent combi boiler issues and how to fix them. The following are the five most common combi boiler issues:1-Boiler pressure drop2-Leaky radiator3-No hot water despite the heating4-The condensate line has become clogged or frozen. 1-Boiler pressure dropA combi boiler's most typical pressure is 1. 5 or below, this is commonly an indication of a water leak. You might not think this is a major problem with your combi boiler, but it might cause it to shut down.