Plumbing, Heating and Pool Repair Guides

Bosch Aquastar 2700ES Water Heater Troubleshooting


WeT HeaD KnowledgeIf you are experiencing problems with your Bosch Aquastar 2700ES Tankless Hot Water Heater than put that money back in your wallet. This Troubleshooting and repair guide should help you isolate and solve whatever problem you may be faced with (hopefully). Being that a hot water heater is an investment, doing the repairs yourself should hopefully help you see more on your return. This article addresses the possible issues that may arise with this hot water heater. Anything from temperature problems, leaks, odors, pressure control and many other things. If you feel that you can not complete these repairs in a safe manner, I urge you to please contact a professional.

PROBLEM: Hot water temperature fluctuates at the tap.

SOLUTION: Unequal pressure in the water flow paths can cause temperature issues, make sure the inlet filter is clean and that there are no obvious blockages. Occasionally the heater is deactivated if the temperature valve is set too high, to fix this you might have to adjust the cold water valve to make sure the temperature is regulated. Make sure your pressure setting is between 40-60 PSI.

PROBLEM: Low water pressure.

SOLUTION: Be sure that you aren’t overloading the hot water heater with multiple applications, the unit can handle up to two of them at one time. Do a gas pressure reading to make sure it is at the appropriate level. You can try lowering the temperature so that the motorized water valve will fully open up to optimize pressure flow. Make sure there are no blockages in the connections either internally or externally.

PROBLEM: Water is not hot enough.

SOLUTION: Make sure the temperature knob is at the right setting and also ensure that the inlet filter is clean. Make sure that all water connections are not obstructed in any way, also be sure that the gas pressure is at the appropriate level. You should also check for a plumbing crossover, to check for this there is a simple test you can do. First, turn off the cold water supply and disconnect the hot water supply. Then put a bucket under the hot water supply, turn the water on and if there is water coming out then you have a plumbing crossover.

PROBLEM: Water is too hot.

SOLUTION: Make sure the temperature knob is set to the right setting and also make sure that the inlet filter is clean. Check the gas inlet screen at the bottom of the unit to make sure there are no obstructions. Also be sure that there are no blockages in any of the water paths internal or external to the hot water heater. A plumbing crossover (mentioned in the previous section) can cause the water to be too hot as well, if this is the case you can do the test that is mentioned above. Lastly, be sure that the gas pressure is at the correct level.

PROBLEM: Too much noise while heater is on.

SOLUTION: Make sure that there is proper ventilation, if the pipes or fittings are the wrong size or the wrong material it will cause the unit to run much louder than normal. Check to see if any of the combustion seals are leaking, the exhaust vent adapter for example needs to be fitted with the proper gasket. Be sure that your hot water heater is getting enough combustion air, the pipes need to be long enough and the room needs to be of a suitable size. Cross contamination between intake and exhaust can also cause burners to operate in a more noisy fashion.

PROBLEM: Burner does not ignite when hot water is turned on.

SOLUTION: Check to see that the outlet the hot water heater is plugged into a properly functioning outlet and that the on/off switch is turned on. Check to see if the fuses on the control board are working correctly. Make sure the cold water supply connection is on the right side of the water heater. Be sure that the inlet filter is clean and that there are no internal or external blockages in any of the water flow connections. As stated in previous sections you want to be sure that you don’t have any plumbing crossovers. You can perform the test mentioned in the section on “water is not hot enough” to see if you need to address a plumbing crossover. The water pressure needs to be at or above 0.65 GPM to avoid shutting off the heater.


  1. I have an Aquastar 125B LP that emits a gas smell when I try to ignite the pilot . It has always been hard to start also .

  2. Pilot light keeps going out and cold water supply line is getting hot like it is pushing hot water backwards and rattling water lines under house

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