This product worked well for about five years. Then I noticed that when it shut down after use, the vent fan would keep running. It didn't run smoothly as normal but vibrated and made a pulsating sound about at a one per second rate. Shutting the unit off and turning back on the fan would continue to run and the unit would not heat water when faucets were opened. I attempted recallibrating but the fan turned on when the switch reached a certain point but there was no spark. Finally I had a certified Bosch service person check it out. He replaced the water valve and the callibration switch and cleaned the critical areas. This was a $600 plus visit from him. Things worked well for about 2 weeks. Then returned to the same behavior as described above. Requested a revisit from the Bosch tech. He opened 3 or four faucets and the unit started right up. Worked another 2 weeks then stopped working again in the same previous manner. I try to start it up every 4 months or so and it will run properly for a couple of days and then. stop. The repair tech has stated that this unit should run relatively trouble free for at least another 10-15 years with limited maintenance. What can I do? Any ideas?


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I sugest putting a higher quaility Nortiz, Takagi, or Rinnai in. You have already wasted $600 on that unit. Better to put the money into a new unit than continue pooring money into fixing that old unit, only to have it fail again 3 years from now in some other way.

Those Bosh Auquastars are a low end unit to begin with. Home Depot used to sell them.

They are lagitamatly hard and time consuming to diagnose (exspensive). Many times, believe it or not, even the manufacturers don't know how to work on them. Even with the correct serial # and model # they will still send you the wrong parts... None of which is the fault of your plumber, which means it is fair for him to charge you for all that time...

I'll check the high limits for continuity. Make sure the flame sensor doesn't have minerals built up on it. And take a quick look for something obvious beyond that. But I won't get into changing out fans, control boxes, or gas valves. To many times it turns into a waste of my customers money.

Even if you don't want to upgrade to a higher quality tankless brand, a new equivalent model Bosch only costs about $600 wholesale (what you plumber can get it for), and with the water, gas, and flue already being there, most plumbers would install it for less than $500...

Rates may vary in your area, but you get the idea... If I'd have been your plumber that's what I'd have been sugesting you do from the start. Some of the guys on this forum will disagree with me, but now that you are $600 in, without a working heater, I'm sure you can follow the logic behind my thinking...



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i have gotten calls from homeowners to put in Bosch units they purchased at HD...i always say no thanks.....sounds like they have to call 20 plumbers just to find someone willing to install it...they have a horrible reputation.....i think your lucky to get 3 years out of it trouble free...id recommend replacing it with a Noritz and cut your losses

i dont know if there are too many experts who repair Bosch tankless units...my opinion was always that it was cheaper to replace it than fix it...the ones i see at HD cost $600

The only Bosch tankless water heaters that are any good are the ES series. But the cost of them is a bit higher than a Navien or some of the other manufactures.

The Rinnai is by far the most popular brand used in my area. They are a high quality unit.

The problem with Rinnai is the venting very expensive if you have a long run. Navien, Bosch ES models and Eternal use PVC venting.