Question about Bosch 2700ES Natural Gas AquaStar AquaStar 2700ES Tankless Water Heat

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Bosch AquaStar 2700ES NG - C7 error

I installed the unit myself and on power on got a C7 error msg.
According to the manual, the primary fan is not rotating.
I checked the power supply and grounding as well as visually inspected the unit inside to make sure there are no loose cable connections.
Any help is appreciated.

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  • gtodorov Feb 01, 2009

    Fixed the problem myself.

    The cables in the control panel attach to the PCB board with connectors that are little flaky.

    The pins in the connector on the multi-wire cable feeding the primary fan were bent outwards and were not making contact with the copper fingers on the PCB board. All it took to fix the problem was a screwdriver and a pin to adjust (bent inwards) the connector pins.

    Overall, a great unit after two days of use but I didn’t expect to have to take it apart to make it work. It’s German engineered after all.

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Hope this helps. Be careful of electrical shock!
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/2700ESTechSupport/Troubleshooting/tabid/1288/Default.aspx
Copy and paste in URL:/Location bar

Posted on Jan 30, 2009

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C7 error code


C7 code has to do with your main fan. Either its not working due to it being blocked or having gotten wet/damaged/power surged, or your control unit isn't supplying the correct 120V to the fan. Your control has a ceramic fuse that you can test as well.
First, look for 120V to either the left or right pair of wires in the molex plug on the fan. if you have voltage, then the fan is bad. If you dont, its either just a fuse, the board is bad, or the fan is bad causing the fuse to blow. Insert the supplied spare fuse, and power up the unit. If it blows the fuse again, its the fan.

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1 Answer

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C7 is displayed when the primary fan (the one in the middle just under the copper heat exchanger) does not spin or the computer does not recognize that it is spinning. There is a plug on the back of the fan. Make sure it is plugged in all the way.
This also happens when the computer gets damaged because the unit is plugged in to an extension cord, power surge or poorly adjusted combustion (most contractors lack the proper equipment to adjust the flame on high efficiency equipment). I have been to over 500 tankless water heater installations and found every one of them were not adjusted at all! It can also be a damaged fan caused by an improperly installed exhaust pipe.

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1 Answer

Water heater continues kick off and we receive a flashing message of c-1


I believe that is C7 as there is no C1 code. This is a fan issue. There is no measure of fan rotation. The unit may have been hit by a power surge and knocked out the fan. It is possible that it may be receiving lower voltage if it is plugged into an extension cord. If it is affected by a surge, the computer may have been hit also. You will need a multi meter to check this out.

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My old Aquastar tankless natural gas water heater used 1/2" gas line. My new Bosch 2700ES -NG says it requires no less than 3/4" inside diameter gas line. Do I have to replace all the gas supply lines...


None !!
3/4 pipe from gas meter or regulator. At low pressure there may not be enough gas flow through a smaller pipe for the boiler when on full bore.
The boiler input pipe will be 1/2" needing a reduction from 3/4 so there is some leeway.
I have about 8' of 1/2 pipe on mine [Bosch Worcester] from the reg. and it is ok.
You could use the existing 1/2 and try. No harm done if insufficient-just replace. If you have some other gas takeoff on the same line a 3/4 pipe up to that take off is most likely.

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Actually, this comment if coming from the math building at LSU!!!! How nice.

Any ways......You probably have a faulty thermo couple. It is the easiest and cheapest thing to do so try that. Most units have reverse threads so keep that in mind when removing. It is identified by a copper wire that leads to the main control unit. It should also be held in-place by some clips that just pinch the copper in place. Replacing the new one will be just the reverse of the removal.

Hope this helps

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