Viessmann Boiler Error Codes

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

158 Viessmann Boiler error codes and diagnostic codes, with causes and troubleshooting steps for each. Select a code, or find your model below.

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Viessmann Boiler error codes list

Code	Meaning	Severity
A.12	Real-time clock battery flat	Low
A.18	Possible condensate back-up in heat cell	Medium
A.19	Temperature limiter has responded	Medium
A.20	Service interval could not be activated	Low
Connection error	Display link lost to HMU	Low
F.5	Sensor circuit fault at plug 33 (X6)	Low
F.7	DHW storage tank sensor open circuit	Medium
F.8	DHW storage tank sensor short circuit	Medium
F.11	Solar collector sensor open circuit	Low
F.12	Solar collector sensor short circuit	Low
F.13	Outside temperature sensor open circuit	Low
F.14	Outside temperature sensor short circuit	Low
F.15	Storage tank sensor open circuit (solar/backup)	Low
F.16	Storage tank sensor short circuit (solar/backup)	Low
F.29	Low loss header sensor open circuit	Low
F.30	Low loss header sensor short circuit	Low
F.49	Flue gas temperature sensor open circuit	High
F.50	Flue gas temperature sensor short circuit	High
F.57	Room temperature sensor open circuit	Low
F.58	Room temperature sensor short circuit	Low
F.59	Supply voltage too low, burner locked out	High
F.62	High limit safety cut-out tripped	Critical
F.63	Flue gas temperature limiter tripped	Critical
F.67	Ionization current outside permitted range	High
F.68	Flame signal present at burner start	High
F.69	Ionization current outside permitted range (valve/electrode check)	High
F.70	BCU internal error	High
F.71	Fan speed too low	High
F.72	Fan idle state not reached	High
F.73	BCU internal communication error	High
F.74	Water pressure too low, burner locked out	High
F.77	BCU data memory error	High
F.89	Internal circulation pump blocked	High
F.91	DIO module communication error	Medium
F.92	ADIO module communication error	Medium
F.94	PlusBus voltage error	Medium
F.100	PlusBus voltage error	Medium
F.104	External fault message input active	Medium
F.142	CAN bus communication error	High
F.143	Fan overheating (air mass flow sensor / recirculation)	High
F.160	CAN bus communication error (external/internal)	High
F.161	BCU data memory access error	High
F.163	BCU memory checksum error	High
F.180	Gas pressure too low	High
F.182	Outlet temperature sensor short circuit	Medium
F.183	Outlet temperature sensor open circuit	Medium
F.184	Supply temperature sensor / high limit short circuit	High
F.185	Supply temperature sensor / high limit open circuit	High
F.299	Time and date incorrect	Low
F.342	BCU communication error	High
F.345	Temperature limiter tripped, auto restart after cooling	High
F.346	Ionization current calibration error	High
F.348	Gas modulation valve fault	High
F.349	Air mass flow not detected correctly	High
F.350	Ionization current outside permitted range (BCU)	High
F.351	Ionization current outside permitted range (BCU)	High
F.352	CO limit inside appliance exceeded	Critical
F.353	Insufficient gas supply, output reduced	High
F.354	Gas modulation valve tolerance outside range	High
F.355	Analogue signal reference check: flame signal at start	High
F.357	Insufficient gas supply	High
F.359	No ignition spark	High
F.361	No or weak flame signal at burner start	High
F.366	Gas valve supply does not switch off	Critical
F.367	Gas valve supply does not switch off	Critical
F.369	Flame loss right after ignition (safety time)	High
F.370	Fuel or modulation valve will not close	Critical
F.372	Repeated flame loss during calibration	High
F.373	Heat transfer too low during calibration	High
F.377	Ionization post-adjustment conditions not met	High
F.378	Flame loss during stabilization or operation	High
F.379	Flame signal missing or insufficient	High
F.380	Flame loss right after ignition (safety time)	High
F.381	Flame loss during operation	High
F.382	Error counter limit exceeded	High
F.383	Possible gas line contamination	High
F.384	Possible gas line contamination	High
F.385	Short circuit on ionization signal 1	High
F.386	BCU faulty	High
F.387	Ionization current ground fault	High
F.388	BCU faulty	High
F.395	IO electrode ground fault	High
F.396	BCU faulty	High
F.399	IO electrode ground fault	High
F.400	BCU faulty	High
F.401	IO electrode ground fault	High
F.402	BCU faulty	High
F.403	IO electrode ground fault	High
F.404	BCU faulty	High
F.405	IO electrode ground fault	High
F.406	BCU faulty	High
F.408	BCU faulty	High
F.410	BCU faulty	High
F.416	Flue gas temperature sensor mispositioned	High
F.417	BCU faulty	High
F.418	BCU faulty	High
F.425	Time synchronization failed	Low
F.430	Gateway communication error	Low
F.446	Supply sensor / high limit deviation	High
F.447	Ionization current signal deviation	High
F.448	Ionization current signal deviation	High
F.449	Program run monitoring error	High
F.450	Program run monitoring error	High
F.451	Program run monitoring error	High
F.452	Program run monitoring error	High
F.453	Sequence synchronization error	High
F.454	Wrong BCU software version	High
F.455	Program run monitoring error	High
F.456	Program run monitoring error	High
F.457	Fan sluggish or blocked	High
F.458	Reset sequence fault	High
F.463	Contaminated combustion air / flue recirculation	High
F.464	Ionization current too low during calibration	High
F.467	Gas supply insufficient during calibration	High
F.468	Ionization current too high during calibration	High
F.471	Sensor circuit fault (call for heat)	Medium
F.473	HMU communication error	High
F.474	Program run monitoring error	High
F.477	Solar differential temperature monitoring	Low
F.517	Remote control not working	Low
F.527	Wrong HMU parameter set	High
F.528	Wrong BCU parameter set	High
F.530	Solar sensor missing or open	Low
F.538	System return sensor open (SDIO)	Low
F.540	Condensate back-up in heat cell	High
F.544	HC2 mixed supply sensor open circuit	Medium
F.545	HC2 mixed supply sensor short circuit	Medium
F.546	HC3 mixed supply sensor open circuit	Medium
F.547	HC3 mixed supply sensor short circuit	Medium
F.548	HC4 mixed supply sensor fault (open circuit)	Medium
F.549	HC4 mixed supply sensor short circuit	Medium
F.574	HC1 room sensor not available	Low
F.666	DHW preheating sensor TS3 open circuit	Low
F.667	DHW preheating sensor TS3 short circuit	Low
F.668	DHW reheating sensor TS4 open circuit	Low
F.669	DHW reheating sensor TS4 short circuit	Low
F.670	Buffer sensor TS3 open circuit	Low
F.671	Buffer sensor TS3 short circuit	Low
F.672	Thermostat-function sensor TS3 open circuit	Low
F.673	Thermostat-function sensor TS3 short circuit	Low
F.691	No combustion air supply feedback	High
F.762	System pressure too low	High
F.763	Gas pressure too high	High
F.764	Lag boiler reports a fault	Medium
F.765	Lead boiler communication error	Medium
I.56	External demand active	Low
I.57	External blocking active	Low
I.59	Parameters restored	Low
P.1	Service interval reached	Low
P.4	Top up heating water	Low
P.8	Service due after burner hours	Low
S.60	Summer mode active	Low
S.74	Heating suppression	Low
S.75	DHW recirculation pump active	Low
S.94	No demand, external hook-up HC1	Low
S.95	No demand, external hook-up HC2	Low
S.96	No demand, external hook-up HC3	Low
S.154	Internal flow switch open	Low

Find codes by Viessmann model

B2HE-85 B2HE-120 B2HE-150 B2HE-199

Boiler troubleshooting guides

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Uneven heating All brands · Boiler
Won't fire All brands · Boiler
Acknowledged fault comes back Viessmann · Boiler
Actuator test: drive fan, burner, pump and 3-way valve by hand Viessmann · Boiler
Clear the service message (P.1 / P.8) Viessmann · Boiler
Condensate not draining, burner shuts down Viessmann · Boiler
Filling and purging programs (20 min auto-stop) Viessmann · Boiler
Lag boilers lose contact with lead boiler (cascade) Viessmann · Boiler
Open the Service menu (password viservice) Viessmann · Boiler
Where the fault history lives Viessmann · Boiler

Homeowner help: Boiler Not Heating: What to Check

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.

Viessmann Boiler error codes list

Find codes by Viessmann model

Boiler troubleshooting guides

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