Safety first: Allow the boiler and piping to cool. Turn off power before working on pumps or valves.

Step 1 – Check all valves: Confirm that all isolation and zone valves are open when there is a call for heat. Manually open motorized valves if possible to test flow.
Step 2 – Verify pump operation: Listen and feel for the system and primary pumps running. If a pump is hot but not circulating, it may be seized and require replacement.
Step 3 – Clean strainers and filters: Shut off valves and clean any strainers on the boiler return or system piping. Debris can severely restrict flow.
Step 4 – Descale heat exchanger: If the system uses hard water and has not been maintained, the heat exchanger may be scaled. A professional can perform a chemical descaling using a pump and approved descaling solution.

Repeated E016 errors indicate a serious flow or scaling issue that should be corrected promptly to avoid heat exchanger damage.

Boiler displays E016 and stops heating, often after running for some time

Possible Causes