The diagram to the right shows how a combi boiler is usually installed the cold feed enters the boiler, is heated in the heat exchanger and then passes out of the domestic hot water outlets when a hot tap is opened. What do you do if a pipe bursts? who do you turn to when you’re looking for an emergency plumber vallejo to inspect a gas leak or unplug a stubborn drain that’s suddenly clogged? Connect with us on linkedin,.