Brilliant news, thanks everyone! There are three main types of gas condensing boiler to choose from: a combi, system and conventional. A this is found on older boilers, which don’t switch off when an optimum house temperature is reached, but rather send the heat to an ‘overflow radiator’ this can waste a lot of energy, so can be a big incentive for a replacement boiler. See our new commercial plumbing page under the services tab! If your plumbing problem is.