Visible water leaking from the bottom of the Pahlen heater cabinet.

Safety first: Turn off power to the heater and shut down the circulation pump. Close isolation valves to the heater to stop water flow. Allow hot components to cool.

Step-by-step checks:

• Locate source of leak: Remove the front and side panels and use a flashlight to trace the leak upward. Look at the inlet/outlet unions, heat exchanger headers, and internal piping.
• Check unions and gaskets: Tighten union nuts slightly by hand, then with a wrench if needed (do not overtighten). Inspect and replace flattened or cracked union gaskets.
• Inspect heat exchanger: Look for green/blue staining (copper) or rust streaks (steel) on the Pahlen heat exchanger. Active dripping from the exchanger body usually indicates a crack.
• Assess freeze damage: If the heater was exposed to freezing temperatures without proper winterization, multiple components may be cracked. In this case, professional evaluation is recommended.

When to stop: If the heat exchanger or manifold is leaking, replacement is typically required and should be performed by a qualified technician.