Aquastar 170 way too hot!

[aktartt]

My Aquastar 170 natural gas tankless has been working faithfully since about 1985. My handyman recently descaled it, and since then the water output has been way too hot. It's been several years since the temperature control knob had any effect, but I've always managed to add enough cold water previously to get the desired water temperature at the faucet, but now if too much cold is added, the burners shut off. (I should mention that the temp sensor was bypassed years ago because the heater wouldn't work at all otherwise.) No doubt the themostat is shot, but of course the most essential parts haven't been available for years now. Does anyone know a workaround for a bad thermostat?

 

[Dana]

Is there any knobs or setscrew adjustments (under sheet metal) that can limit the maximum flame?

Is this the right manual?

See the diagram on p.20. If yours is similar, back off the adustment screw and see if you can get the piston to move up/down with a flat tool, and see if the flame goes up/down in response. Even if the feedback aspects don't work, you may be able to set the flame level to some lower fixed-rate with the set screw if the piston moves.

 

[Sponsor]

 

[aktartt]

Is there any knobs or setscrew adjustments (under sheet metal) that can limit the maximum flame?

Is this the right manual?

See the diagram on p.20. If yours is similar, back off the adustment screw and see if you can get the piston to move up/down with a flat tool, and see if the flame goes up/down in response. Even if the feedback aspects don't work, you may be able to set the flame level to some lower fixed-rate with the set screw if the piston moves.

Thanks for your response. Yes, that is the correct manual. However, backing off the calibration screw doesn't cause the flames to modulate in any way, and there is very little up-and-down movement of the piston. The flames don't change either when I turn the temp control knob from 2 to 8 and vice verse. They are just stuck at a roaring high level. In the troubleshooting section of the manual, it says that if the calibration screw is screwed down all the way and the water is still too hot, then the thermostat is bad. I don't see any way to limit the gas flow without messing with the main gas valve at the wall. I was wondering if anyone had a workaround involving a generic thermostat.

 

[Dana]

It's the up/down of the piston that should be modulating the flame. The set screw is only a limiter/adjuster for the thermomechanical feedback. If the piston is sticky it won't move when the setscrew is adjusted. If you can get enough free-space between the mechanical arm that SHOULD be moving the piston to slip a flat screwdriver in there or a pair of tiny needle-nosed pliers you might be able to get it to move and adjust the flame, even if it can no longer move freely enough for it to automatically adjust the flame.

 

[aktartt]

It's the up/down of the piston that should be modulating the flame. The set screw is only a limiter/adjuster for the thermomechanical feedback. If the piston is sticky it won't move when the setscrew is adjusted. If you can get enough free-space between the mechanical arm that SHOULD be moving the piston to slip a flat screwdriver in there or a pair of tiny needle-nosed pliers you might be able to get it to move and adjust the flame, even if it can no longer move freely enough for it to automatically adjust the flame.

Okay, thanks, I tried this. By backing off the adjustment screw, I was able to insert a flathead screwdriver between the bottom of the piston and the support arm. With the burners activated, I'm able to push the piston up and then push it down. But the burners don't modulate at all. It's worked great for more than thirty years, so I guess I should be willing to accept the fact that I probably need a new tankless. Thanks for your suggestions.

 

[Dana]

If you're looking for a similar, almost drop-in comparable & inexpensive tankless replacement, Marey imports some pretty good "dumb as a box o' rocks" tankless units with similar innards for under $350 (can even be ordered through Home Depot, but may be cheaper elsewhere.) Any of the 16 liter versions have comparable maximum firing rate to the ELM Aquastar 170, but much better modulation/temperture control at low flow rates than the ELM ever had even when new.

If you never needed the max output of the -170 the 10 liter version is even cheaper (under $250) and has even better temperature control at low flow. It's still good for one full-flow shower, but not two.

 

[aktartt]

If you're looking for a similar, almost drop-in comparable & inexpensive tankless replacement, Marey imports some pretty good "dumb as a box o' rocks" tankless units with similar innards for under $350 (can even be ordered through Home Depot, but may be cheaper elsewhere.) Any of the 16 liter versions have comparable maximum firing rate to the ELM Aquastar 170, but much better modulation/temperture control at low flow rates than the ELM ever had even when new.

If you never needed the max output of the -170 the 10 liter version is even cheaper (under $250) and has even better temperature control at low flow. It's still good for one full-flow shower, but not two.

Thank you! I'm definitely looking for something as simple as my Aquastar. I don't need bells and whistles.

 

[Ladiesman217]

I own an Aquastar 125vp.

https://terrylove.com/forums/index.php?threads/elm-aquastar-125vp-ng-tankless.73861/

The thermostat probe modulates the burners as the water temperature varies.

https://www.bosch-climate.us/files/201109161831010.TWH-V-04_Checking_the_tstat.pdf

If the thermostat is bad, the hot water temperature can only be adjusted with the temperature knob. The temperature knob will vary the flame intensity as you turn the temperature knob up and down.

I would temporarily remove the calibration screw and pull out the thermostat piston assembly from the housing. Inspect the piston per the pdf above. Then test the unit too see if the burners activate when you draw water.

https://www.bosch-climate.us/files/201109161858280.TWH-V-06_Replacing_tstat.pdf

 

[Ladiesman217]

Aquastar service bulletins.

https://www.bosch-climate.us/bosch-hot-water/aquastar-service-bulletins/vp-series-bulletins.html