Bosch Therm 250SX, GWH 635ES and 2400E gas tankless error code C7
No fan speed signal from the fan
Which models this applies to. This page covers the Bosch Therm 250SX, GWH 635ES and 2400E gas tankless codes.
What is specific to the Therm 250SX, GWH 635ES and 2400E gas tankless platform
Condensing gas tankless platform with a condensing heat exchanger, an induction fan and a flue gas limiter. Four of its codes, A2, A7, A9 and C1, mean something completely different on the Greentherm T9000 platform, and the gas pressure ranges published for it differ from the T9000 ranges, so the code has to be read against the model family rather than as a Bosch code.
Your control board prints the code as text, for example F01 or EE3, so you read it off the display rather than counting blinks. The printed number is the fault itself, not a position in a table.
Quick answer
On Bosch Therm 250SX, GWH 635ES and 2400E gas tankless, C7 is a fault. It means no fan speed signal from the fan. A first thing to check: Water or condensation damage from improper installation.
- Applies to
- Bosch Therm 250SX, GWH 635ES and 2400E gas tankless
- Bosch Therm 250SX, GWH 635ES and 2400E gas tankless codes · Water Heater
- Type of code
- Fault
- Urgency: Needs attention soon
- First safe check
- Open the fan through the air scoop and inspect it for debris, water damage or physical damage.
What C7 means on this model
The control is getting no fan speed feedback at all. Bosch associates this with water or condensation damage from improper installation, and warns that a water damaged fan means the gas valve is probably damaged too, so replacing the fan alone will not fix the heater.
Symptoms you will notice
- The unit shows C7
- The unit will not complete a start sequence
- No hot water
- Evidence of water or condensation inside the unit, especially after a flood, a leaking roof or a new installation
Common causes
The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:
- Water or condensation damage from improper installation
- A damaged or failed fan assembly
- Debris blocking the fan
What you can safely check
These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.
- Open the fan through the air scoop and inspect it for debris, water damage or physical damage.
- Check the flue pipe for a blockage once the fan checks out.
- Look for evidence of where water entered, because a fan that has been wet tells you the problem is larger than the fan.
Do not do these
- ×Do not replace the fan and declare the heater fixed when the fan assembly was damaged by water. Bosch states the gas valve is likely damaged as well.
- ×Do not return a water-damaged heater to service on a new fan alone, because the gas valve is the part that has to be trusted to shut gas off.
When to call a technician
Book a technician, do not keep resetting it
This fault will not clear on its own. Every power cycle gives the control one more failed attempt, and repeated attempts are what turn a cheap part replacement into a seized or contaminated system.
- This is a fuel-burning appliance, so treat anything involving a burner, gas valve or flue as technician work. If you smell gas at any point, leave the property and call the gas utility from outside rather than continuing to diagnose.
- If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.
A technician job. This one implies water intrusion and a possible gas valve replacement, and Bosch explicitly warns against a fan-only repair.
What it costs to fix
Parts
Fan assembly $150 to $400. Gas valve $180 to $400, and it is the part most likely to be needed after water damage.
Labor
Two to four hours once the unit is drained and the heat exchanger is out of the way.
DIY or technician
A technician job. This one implies water intrusion and a possible gas valve replacement, and Bosch explicitly warns against a fan-only repair.
Typical US part and labor ranges, 2026. They vary by region, model and contractor, so treat them as a planning figure, not a quote.
Scope of this code
- Code table
- Bosch Therm 250SX, GWH 635ES and 2400E gas tankless codes
- How this model reports the code
- Printed on the control display
- Models in scope
- Bosch Therm 250SX, GWH 635ES and 2400E gas tankless
- How this platform differs
- Condensing gas tankless platform with a condensing heat exchanger, an induction fan and a flue gas limiter. Four of its codes, A2, A7, A9 and C1, mean something completely different on the Greentherm T9000 platform, and the gas pressure ranges published for it differ from the T9000 ranges, so the code has to be read against the model family rather than as a Bosch code.
- Checked
- Confirm on your own unit
- Find the model number on the data plate, then check this code in the service manual for that model. Manufacturers revise code tables between model years, and a revised board can renumber a fault.