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 Bosch Aquastar low flame issue
Author: adkroot (NY)

My Bosch Aquastar 125blp recently wasn’t getting water as hot as usual, and it got progressively worse over a few days. The water valve selector screw made minimal difference in flame height/intensity which is very low. Burner is clean and free of any debris. Cleaned the cold water intake screen, and removed the water valve to flush and clean it, with no change in heating capability. The venturi was pretty corroded, but the openings were clear and unobstructed. I installed a new pushrod assembly in the water valve, and still no change. When I manually pushed the piston on the gas valve, which operated smoothly, I could bring the flame up to its maximum output. The watervalve selector screw seems to have some wear at the end that actuates actual adjustment, but I’m not positive that this is the issue. I ordered a replacement watervalve and I’m hoping that there’s wear issues with the old one that I can’t see that the new one will remedy, but I’m also wondering if that nearly $300 upgrade might be money thrown away if the issue is in the gas valve and after installing the water valve I won’t be able to return it. I’m also assuming the gas regulator right at the unit is operating fine since when I manually pushed the piston on the gas valve I was able to get the flame up, but maybe I was pushing it farther than the watervalve pushrod needs to. I just put a new heat exchanger in this heater, and this is an offgrid cabin with an electric system that would struggle with a heater with electric requirement, and there’s no room for a tank water heater.
Any ideas? Thanks, Dan

*EDIT* The watervalve was the issue. Under 5 minute swap out with replacement valve and the heater is good as new.



Edited 1 times.

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