Bosch Water Heater: Won't Start or Turn On
On gas units, typically a thermocouple or igniter fault; on electric, a tripped reset or failed element. Upload a photo of your Bosch Water Heater and fixRAgent's AI pinpoints the exact failed part.
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In the next five minutes
Safe first steps, before the call. Nothing here needs a tool.
If you smell gas, a carbon monoxide alarm sounds, or anyone feels dizzy or sick: don’t touch any switch or plug, leave and get everyone out, then call 911 or the gas company from outside.
No gas smell? Turn the water heater’s gas control knob to OFF if it’s gas, or switch off its breaker if it’s electric.
Take a photo of the tank, the floor and its label, without opening anything.
Everything else about this problem
Is it an emergency?
Is a Bosch water heater that won't start an emergency?
Rarely an emergency. Check its breaker and, on a gas unit, the display or the label by the gas control. Stop and call a pro if it keeps tripping the breaker, smells like burning, or you smell gas.
Symptoms & causes
Your Bosch water heater may show no signs of life, no pilot light, or no display, indicating a complete power failure or a lockout. Common root causes include tripped circuit breakers, a faulty thermostat, a failed igniter, or issues with the gas supply to the unit. For tankless models, a clogged filter or a sensor malfunction can also prevent startup.
Tools & parts
You will need a multimeter to test electrical continuity and voltage, which can be purchased. A replacement Bosch igniter or flame sensor might be required. Additionally, a screwdriver set and a wire brush for cleaning connections are essential.
Safety first
Always begin by shutting off the electrical power to the water heater at the circuit breaker and turning off the gas supply valve to prevent electrocution or gas leaks. Ensure proper ventilation and be aware of potential carbon monoxide hazards if the unit is gas-fired and not combusting properly. Never attempt repairs if you smell gas; evacuate and call a professional immediately.
When to call a pro
If the main control board or gas valve is suspected to be faulty, these are complex components that typically require a certified Bosch technician for testing and replacement. Issues involving the heat exchanger or internal plumbing leaks also fall under professional repair due to the specialized tools and knowledge required. Furthermore, any persistent error codes that cannot be cleared by basic troubleshooting indicate a deeper system failure best addressed by an expert.
Questions people ask
What if my Bosch water heater's pilot light won't stay lit?
A common cause for a pilot light not staying lit is a dirty or faulty thermocouple, which senses the flame and tells the gas valve to stay open. Try gently cleaning the thermocouple with fine-grit sandpaper or replacing it if cleaning doesn't resolve the issue.
My Bosch tankless water heater shows an error code, what should I do?
Consult your Bosch owner's manual for the specific error code meaning, as it often points directly to the failing component or system. Many codes can be resolved by simple actions like cleaning filters or resetting the unit, but persistent codes may indicate a sensor or board issue.
Could a power surge prevent my Bosch water heater from starting?
Yes, a power surge can trip the circuit breaker or damage the control board, preventing the unit from turning on. Check your home's circuit breaker panel and reset any tripped breakers, and inspect the water heater's internal fuse if accessible and applicable to your model.
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Find The Broken Part
Upload a photo of your Bosch Water Heater or its model number tag. The Triage Profile says what it is, how urgent it is, and who to call.