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Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 20735
Experience:  Licensed Master plumber with 40+ yrs. experience.
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My Bosch aquastar tankless HW heater does not fire. The

Customer Question

My Bosch aquastar tankless HW heater does not fire. The pilot goes on but the main burners do not ignite
Submitted: 1 year ago.
Category: Plumbing
Expert:  Rick replied 1 year ago.

I can link you to the troubleshooting guide for this type of issue. You'll need a multi-meter to troubleshoot this. The troubleshooting is too involved for me to tell you what to do here. It would take forever. Or are you just looking for some likely causes so you don't get hosed by a repair tech? Let me know if you want the guide. I can answer follow up questions if you have any while following the guide.

Customer: replied 1 year ago.
I have the guide from the manual but itt is not too helpful
Customer: replied 1 year ago.
If possible I woulld like to repair it myuself. I have good homeowner skills but live in a rural area where not many service techs available
Expert:  Rick replied 1 year ago.

I just noticed your model number. It looks like this model has a standing pilot so the service bulletin I was referring to doesn't apply here. The most common reason for the unit to not respond is a clogged inlet filter on the cold water inlet. Have you cleaned this filter/screen?

Customer: replied 1 year ago.
No, I have not cleaned the water filter, but the flow through is normal so I thought that was not the problem. Am I wrong?
BTW, it is a piezo ignitor. Come on when I run water but pilot shuts in 10 secs or so without igniting burner.
Expert:  Rick replied 1 year ago.

Cleaning the filter is the first thing you need to do whether you think the flow is good or not. It's also the easiest thing to do

Customer: replied 1 year ago.
OK, I will do that and get back to you when I am done.
Expert:  Rick replied 1 year ago.

I'm not going to be on much longer. If you don't get back to me in time just relist the question and one of our West Coast experts should pick it up. Or I can get back to you in the morning ~8 am EDT

Expert:  Rick replied 1 year ago.

If cleaning the filter doesn't work and you've tried cleaning the flame sensor (as described in the manual) then we're down to the water valve (not the shut offs). Thw water valve is what senses the water flow and modulates the burner flame accordingly. It is a maintenance item. Here is the service bulletin for rebuilding it

You can also move on to item 7 in the manual, checking the voltage at the electro valve

Customer: replied 1 year ago.
The filter was clogged but also had a hole. I took it out but the problem was not solved.
Expert:  Rick replied 1 year ago.

Then you need to test the voltage as described above and possibly rebuild the water valve.