Bosch Water Heater Error Codes — Meanings, Causes & Repair in Greater Vancouver

Seeing a fault code on your Bosch water heater? This guide explains what the most common Bosch water heater error codes mean, what’s safe to check yourself, and when to call HeatLand’s licensed, TSBC-certified gas technicians for Bosch water heater repair across Metro Vancouver and the Fraser Valley.

The codes below apply across common Bosch models (Greentherm, Therm). Meanings follow Bosch’s documented fault codes — always confirm against your unit’s own manual, because exact wording can vary by model, control board and firmware.

How to read Bosch water heater error codes

Two-character alphanumeric codes shown on the front-panel digital display. Letter prefix groups the fault: 'A' = monitoring / temperature-sensor codes, 'C' = combustion / fan / venting codes, 'E' = lock-out / overheat / ignition codes, 'F' = ignition-rod / gas-valve codes. Older Therm/AquaStar models share the E0/E1/E2/E9/EA/EC core codes. Most soft faults are cleared by a single reset (hold the On/Off button ~3 seconds on touch-control Greentherm units, or press RESET on the front panel of Therm units). Bosch domestic-hot-water heat-pump units use a separate E07-E11 lock-out scheme.

Bosch water heater error codes & what they mean

These are the Bosch water heater codes our Greater Vancouver technicians see most. Anything marked pro repair involves gas, electrical, sealed-combustion or control-board work that must be done by a licensed gas technician (TSBC-certified in BC) — never open gas or electrical components yourself.

Code	What it usually means	Common causes	Safe to check yourself
A0	Cold-water or hot-water temperature sensor fault pro repair	Loose or corroded sensor wiring connector; Failed inlet/outlet temperature sensor	Power the unit off and back on (single reset)
A1	Temperature inside the cabinet is above 158 F (70 C) pro repair	High surrounding/ambient air temperature; Flue gas leakage inside the cabinet; Restricted air circulation around the appliance	Confirm the area around the unit is not unusually hot and has clear airflow; Power the unit off and back on (single reset)
A2	Flue gas limiter activated / tank temperature sensor not properly installed (hot flue gas detected in the cabinet on condensing models) pro repair	Blocked or improperly terminated exhaust venting; Damaged heat-exchanger gasket allowing flue gas into the cabinet; Tank/contact temperature sensor not seated correctly	Visually confirm the outdoor vent terminal is clear of snow, debris, or nests; Power the unit off and back on (single reset)
A3	Flue (exhaust) gas temperature sensor fault pro repair	Disconnected or damaged flue-gas sensor wiring; Failed flue-gas temperature sensor	Power the unit off and back on (single reset)
A4	Cabinet air temperature sensor fault pro repair	Disconnected or damaged cabinet air sensor wiring; Failed cabinet air temperature sensor	Power the unit off and back on (single reset)
A5	Primary heat-exchanger gas temperature sensor fault pro repair	Disconnected or damaged sensor wiring; Failed heat-exchanger gas temperature sensor	Power the unit off and back on (single reset)
A6	Inlet water temperature sensor fault pro repair	Disconnected or damaged inlet sensor wiring; Failed inlet water temperature sensor	Confirm the water supply to the unit is fully on; Power the unit off and back on (single reset)
A7	Heat-exchanger / outlet water temperature sensor fault (poor sensor contact, loose wiring, or defective sensor) pro repair	Sensor not making good contact with the copper pipe; Loose or corroded sensor wiring; Failed outlet/heat-exchanger temperature sensor	Power the unit off and back on (single reset)
A8	Outlet water temperature sensor fault pro repair	Disconnected or damaged outlet sensor wiring; Failed outlet water temperature sensor	Power the unit off and back on (single reset)
A9	Incorrect output power, or hot-water temperature sensor not properly installed (commonly a sensor-contact / wiring status condition) pro repair	Incoming gas pressure outside specification; Hot-water/outlet sensor not seated correctly against the pipe; Loose sensor wiring	Confirm the gas supply valve to the unit is fully open; Power the unit off and back on (single reset)
AA	Flue gas temperature above 356 F after the primary heat exchanger and/or above 176 F at the exhaust sensor pro repair	Scale build-up reducing heat transfer; Inlet water temperature above the allowed limit; Restricted exhaust venting	Confirm the outdoor vent terminal is clear and unobstructed; Power the unit off and back on (single reset)
AD	Maximum power output of the water heater has been derated (reduced) due to insufficient combustion air or restricted venting pro repair	Insufficient air supply / blocked air intake; Blockage in intake or exhaust piping; Installation not meeting venting requirements in the manual	Confirm both the intake and exhaust vent terminals outside are clear of snow, debris, or nests; Power the unit off and back on (single reset)
C1	Combustion / venting fault group: obstruction in the venting or clogged burner (dust, pollen, debris, or insects) pro repair	Obstruction in the intake or exhaust venting; Burner clogged with dust, pollen, debris, or insects; Dirty air filter	Confirm the outdoor intake and exhaust terminals are clear of obstructions; Power the unit off and back on (single reset)
C2	Combustion / venting fault group: obstruction in the venting or clogged burner pro repair	Obstruction in the intake or exhaust venting; Burner clogged with dust, pollen, debris, or insects; Dirty air filter	Confirm the outdoor intake and exhaust terminals are clear of obstructions; Power the unit off and back on (single reset)
CE	Combustion / venting fault group: obstruction in the venting or clogged burner pro repair	Obstruction in the intake or exhaust venting; Burner clogged with dust, pollen, debris, or insects; Dirty air filter	Confirm the outdoor intake and exhaust terminals are clear of obstructions; Power the unit off and back on (single reset)
CF	Combustion / venting fault group: obstruction in the venting or clogged burner pro repair	Obstruction in the intake or exhaust venting; Burner clogged with dust, pollen, debris, or insects; Dirty air filter	Confirm the outdoor intake and exhaust terminals are clear of obstructions; Power the unit off and back on (single reset)
C5	Fault in the bypass valve pro repair	Loose or damaged bypass-valve wiring connector; Failed bypass valve	Power the unit off and back on (single reset)
C7	Fan not working (no fan rotation detected) pro repair	Loose or disconnected fan wiring; Blocked or seized fan; Failed combustion fan or speed sensor	Confirm the outdoor vent terminals are clear; Power the unit off and back on (single reset)
C8	Main water valve disconnected pro repair	Disconnected or damaged water-valve wiring connector	Close and reopen a hot-water tap to re-trigger demand; Power the unit off and back on (single reset)
C9	Barometric pressure sensor fault pro repair	Failed barometric pressure sensor on the Electronic Control Unit (ECU)	Power the unit off and back on (single reset)
E0	Internal control-unit hardware/software failure pro repair	Control-unit (PCB) fault; Transient electrical glitch	Press RESET on the front panel (single reset), or hold the On/Off button ~3 seconds on touch-control units
E1	Outlet (hot water) temperature too high – outlet temperature above ~203 F (95 C). Often associated with scale build-up in the heat exchanger pro repair	Scale / lime build-up in the heat exchanger; Outlet sensor not properly attached or scaled over; Low water flow	Confirm the water supply is fully on and a hot tap is producing adequate flow; Press RESET / hold On/Off ~3 seconds (single reset)
E2	Inlet (cold) water temperature sensor fault – cold-water sensor detects a temperature below ~36 F (2 C) pro repair	Very cold incoming water near freezing; Failed inlet water temperature sensor; Loose sensor wiring	Confirm the water supply is fully on; Press RESET / hold On/Off ~3 seconds (single reset)
E9	Overheat sensor (ECO / temperature limiter on the heat exchanger) has tripped or shows an open circuit pro repair	Heat exchanger overheating due to scale / lime build-up; Blocked or out-of-spec venting; Open or broken overheat thermal fuse / damaged limiter wiring	Confirm the outdoor vent terminals are clear and unobstructed; Confirm the water supply is fully on; Press RESET / hold On/Off ~3 seconds (single reset)
EA	Ignition failure – the burner attempted to ignite (typically three times) with water flow sensed but no flame ionization was detected pro repair	No or insufficient gas supply / wrong fuel type; Gas pressure below specification; Faulty or dirty spark/ignition electrodes	Confirm the gas supply valve to the unit is fully open and other gas appliances work; Confirm the outdoor vent terminals are clear; Press RESET / hold On/Off ~3 seconds (single reset)
EC	Flame loss during operation – combustion was established but the flame dropped out (no ionization) while hot-water demand continued pro repair	Gas supply pressure dropping during operation; Wrong fuel type for the unit; Rain / condensation entering the exhaust	Confirm the gas supply valve is fully open; Confirm the outdoor vent terminals are clear and properly terminated; Press RESET / hold On/Off ~3 seconds (single reset)
F7	Ionization (flame-sensing) rod problem – flame signal detected when no flame should be present pro repair	Dirty or shorted ionization/flame-sense rod; Damaged ionization wiring; Gas-valve leakage	Press RESET / hold On/Off ~3 seconds (single reset)
FA	Gas valve circuit fault – gas valve circuit not closing (possible gas valve not de-energizing) pro repair	Faulty gas valve; Gas-valve wiring or relay fault on the control board	Press RESET / hold On/Off ~3 seconds (single reset)
E07	Heat-pump water heater code – reserved for internal technical use only (not a field-serviceable fault) pro repair	Internal diagnostic state	Power the unit off and back on (single reset)
E09	Heat-pump water heater lock-out – fault in the compressor system pro repair	Compressor thermal-protection contact open; High- or low-pressure switch tripped; Circulation pump malfunction or low water flow	Confirm the water supply / tank is filled and flow is present; Power the unit off and back on (single reset)
E10	Heat-pump water heater lock-out – fault in the electrical backup heating element (over-temperature detected) pro repair	Backup element over-temperature trip; Scale build-up on the electric resistance element; Failed resistance element or thermostat	Power the unit off and back on (single reset)
E11	Heat-pump water heater lock-out – fault in the compressor system (similar conditions to E09) pro repair	Compressor thermal-protection contact open; Pressure switch tripped; Low water flow / pump fault	Confirm the water supply / tank is filled; Power the unit off and back on (single reset)

Bosch water heater codes we get called for most

EA — Ignition failure – the burner attempted to ignite (typically three times) with water flow sensed but no flame ionization was detected

Typical causes include no or insufficient gas supply / wrong fuel type; gas pressure below specification; faulty or dirty spark/ignition electrodes. A few things are safe to check yourself (Confirm the gas supply valve to the unit is fully open and other gas appliances work; Confirm the outdoor vent terminals are clear), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes EA on Bosch water heaters throughout Greater Vancouver.

EC — Flame loss during operation – combustion was established but the flame dropped out (no ionization) while hot-water demand continued

Typical causes include gas supply pressure dropping during operation; wrong fuel type for the unit; rain / condensation entering the exhaust. A few things are safe to check yourself (Confirm the gas supply valve is fully open; Confirm the outdoor vent terminals are clear and properly terminated), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes EC on Bosch water heaters throughout Greater Vancouver.

C9 — Barometric pressure sensor fault

Typical causes include failed barometric pressure sensor on the electronic control unit (ecu). A few things are safe to check yourself (Power the unit off and back on (single reset)), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes C9 on Bosch water heaters throughout Greater Vancouver.

E1 — Outlet (hot water) temperature too high – outlet temperature above ~203 F (95 C). Often associated with scale build-up in the heat exchanger

Typical causes include scale / lime build-up in the heat exchanger; outlet sensor not properly attached or scaled over; low water flow. A few things are safe to check yourself (Confirm the water supply is fully on and a hot tap is producing adequate flow; Press RESET / hold On/Off ~3 seconds (single reset)), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes E1 on Bosch water heaters throughout Greater Vancouver.

Is it safe to keep running a Bosch water heater with a fault code?

Most Bosch fault codes put the water heater into a safe lockout for a reason. You can safely check the basics — the gas supply on, the pilot light or igniter, the temperature dial setting, the breaker on (power-vent/electric/hybrid models), and no water leaking around the tank — and restart it once. If the code returns, stop and book a technician. If you smell gas, leave the building and call your gas utility’s emergency line or 911 first. If a carbon-monoxide alarm sounds, get everyone out and call 911. Never cap or block the temperature & pressure (T&P) relief valve, and don’t keep relighting a pilot that won’t stay lit.

Bosch water heater repair across Greater Vancouver

HeatLand has kept Metro Vancouver homes comfortable since 1999. Our licensed, insured technicians diagnose and repair Bosch water heaters — pilot and ignition faults, gas-control (status-light) codes, sensor and thermostat errors, vent and air-intake blockages, leak shut-offs, and (on hybrid/heat-pump and tankless models) control-board and component faults — including units we didn’t install. We’re brand-agnostic, carry common parts, and give you an honest repair-or-replace assessment with upfront pricing and a free estimate. If your water heater is beyond economical repair, we’ll show you right-sized, high-efficiency replacement options and the rebates available.

Need it sorted fast? We offer priority emergency water heater repair. Explore Water Heater services, browse all water heater error codes by brand, or request a free estimate.

Bosch water heater service areas

We repair Bosch water heaters across Greater Vancouver and the Fraser Valley, including:

Bosch water heater error code FAQs

Can I reset my Bosch water heater myself?

Yes — power-cycling the reset button once is generally safe after you’ve checked the basics (the gas supply on, the pilot light or igniter, the temperature dial setting, the breaker on (power-vent/electric/hybrid models), and no water leaking around the tank). If the water heater faults again right away, stop and note the code — repeatedly resetting a water heater that keeps locking out can mask a real problem. Call a licensed, TSBC-certified gas technician to diagnose it.

What does the Bosch A0 code mean?

On Bosch water heaters, A0 commonly indicates cold-water or hot-water temperature sensor fault. Confirm the exact meaning against your unit’s manual — codes can vary by model and series — and have the repair done by a licensed, TSBC-certified gas technician. HeatLand fixes this across Greater Vancouver.

Do you repair Bosch water heaters you didn’t install?

Yes. HeatLand is brand-agnostic and services Bosch water heaters throughout Metro Vancouver and the Fraser Valley, whether or not we installed the unit. We carry common parts and give you an honest repair-or-replace assessment.

Is a Bosch water heater fault code an emergency?

No heat in cold weather is worth treating urgently. If you smell gas, leave the building and call your gas utility’s emergency line or 911 first. If a carbon-monoxide alarm sounds, get everyone out and call 911. Never cap or block the temperature & pressure (T&P) relief valve, and don’t keep relighting a pilot that won’t stay lit. For priority water heater repair across Greater Vancouver, call (604) 330-3812.

How much does Bosch water heater repair cost in Vancouver?

It depends on the fault. Many Bosch codes point to sensors, ignition or pump parts — usually far cheaper than replacement. We give upfront pricing and a free estimate before any work.

More Water Heater error-code guides

HeatLand repairs every major water heater brand across Greater Vancouver. More brand guides: