Bosch 2400ES tankless is overheating the water


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Old 09-14-15, 08:40 PM
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Bosch 2400ES tankless is overheating the water

Hi all,

I've been having issues with my Bosch 2400ES unit. This is actually a replacement for an earlier model because the earlier model was also overheating the water. I call for 114 degree water. The old unit would overheat the water on the minimum burn rate during the hottest summer months when the incoming water temp was up.

The new unit has a much lower minimum BTU output and until this year, I haven't had any issues with it. I've had it for probably 4 years installed, and when on, the flame graph shows I have steps lower than the current fire rate.

Symptom: Call for water from unit, Unit fires, 114 flashes as the unit comes up to temp and then it stays solid indicating the temp was reached. Use the water without any increase or decrease in flow rate and the output temp begins creeping up.

I flushed the unit with 4 gallons of white vinegar for approx 45 minutes and no noticeable change.

Recently, I have been getting an AE error code and unit fails to fire. I need to hit RESET and it's back working.

I have a two lead thermometer I can slap on inlet and outlets to determine the call doesn't exceed the minimum temp rise. I don't suspect that as an issue as the unit generally holds the temp well enough. The creeping is kinda of hit or miss with more hits lately.

I called bosch but their repair manual is not for consumer distribution. I did install the unit myself and I worked in HVAC design, but apparently that doesn't qualify.

Anyone have any good bits of advice as to what to test?
 
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Old 09-14-15, 09:04 PM
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I've located some Bosch TSB's that pertain to your unit.
Bosch Tankless Water Heaters: Bosch 2400ES/2700ES Service Bulletins


Possibly more help here....
Technical Support for Bosch Tankless Water Heaters Support
 
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Old 09-18-15, 05:30 AM
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thanks! will investigate this weekend
 
 

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