We had a boiler and hot water tank installed in Sept 2012. A fan was also installed to both of them to the outside (we were told this fan would work for both). The problem we are having is that the vent from the boiler to the fan "sweat". There is enough condensate dripping that we have to put a cloth underneath to absorb it. We have not had to turn the thermostat up as yet as we have electric heaters that do a sufficient job. That being said, the heat does automatically kick in when it goes below 10 degress celsius. Even so, there is still condensate on the vent. We have been told that we HAVE to turn the thermostat up to about 20 degress to eliminate the condensate on the vent. So, silly question ... shouldn't we be able to turn the thermostats up or down when we like and not just to "dry the condensate on the vent"? Is the guy trying to pull a fast one on us? We thought we could save on our gas bill, but it looks like it will be costing us more if we HAVE to keep it on. The other option that he gave us yesterday was that we should get another fan ... he says its the hot water tank that is causing the condensate. I've included a picture. The area circled is where we get the condensate. He's already shortened the vent leading to the fan, but that didn't help. Is there something else that can be done. Thanks.