HTP Error Codes & Diagnostic Codes

Updated October 16, 2026 · by Aurora Star Tech Inc.

HTP error codes and diagnostic codes: look up a code to see what it means, the likely causes and the steps to fix it.

HTP error codes by equipment type

HTP Boiler error codes

Code	Meaning
CASCADE MASTER READY	Cascade master ready
CASCADE NO FOLLOWER	Cascade - no follower
CASCADE NO SENSOR	Cascade - no system sensor
DHW	Temperature blocking - DHW demand
E03	System sensor failure (cascade)
E07	Flue temperature high
E19	Line voltage frequency out of range
F00	Water high temperature (ECO)
F01	Flue temperature switch / low water
F02	Supply sensor failure
F03	Return sensor failure
F04	Flue sensor failure
F05	Supply temperature high
F06	Return temperature high
F09	No flame on ignition
F10	Flame loss
F11	False flame signal
F13	Fan speed error
F20	Condensate full
F31	Program error
FL	Low water flow
FLU	High flue pressure
FOU	Outdoor sensor fault
GAS VALVE ON / RUN	Ignition then run status
LOCKOUT	Lockout (display message)
LOU	24 volt supply low
MAINTENANCE REQUIRED	Service reminder
PP	Control programmed
PRO	Low water pressure
SERVICE PUMP CH / DH / SH	Pump service mode
SERVICE RUN	Test mode running
TT	Temperature blocking - thermostat (TT) demand

Find codes by HTP model

EL-80 LP EL-80 N EL-110 LP EL-110 N EL-150 LP EL-150 N EL-220 LP EL-220 N EL-299 LP EL-299 N EL-399 LP EL-399 N

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.

HTP error codes by equipment type

HTP Boiler error codes

Find codes by HTP model

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