Heat exchanger safety high limit or flue gas temperature limiter has tripped.
Check flue gas safety high limit and leads for interruptions or shorts, and replace if defective.
Check heat exchanger safety high limit and leads for interruptions or shorts, and replace if defective.
Check the operating pressure.
Check temperature limit; replace if defective.
Check pump capacitor; replace pump if defective.
Check PCB fuse, replace if blown (6.3 A fuse according to IEC default).
Purge the appliance
Check heat exchanger on the DHW side; replace if clogged.
