🔍 Key Concepts

• Fuel oil heaters often use steam or hot water on one side and fuel oil on the other, separated by tubes or plates • An internal leak means the barrier between the two fluids has failed, allowing one to get into the other • Think about which side is at higher pressure in normal operation

💭 Think About

• If the tube or coil inside the heater develops a crack, which fluid is most likely to be forced into the other, based on usual system pressures? • What would be the most direct and immediate result of that unwanted mixing inside the heater, before thinking about long‑term effects like carbon buildup or pressure changes? • Look at each choice and ask: which one describes a direct consequence of two fluids mixing across a failed barrier, rather than a secondary symptom?

✅ Before You Answer

• Identify which medium (fuel or heating medium such as steam/water) is normally at higher pressure in a fuel oil heater system • Decide which side (fuel side or drain side) that higher‑pressure medium would most likely flow into if a leak occurs inside the heater element • Rule out options that describe effects that are indirect or longer‑term symptoms, rather than the first, straightforward result of two fluids mixing