Aquastar 125 BO flue gas sensor

[chasimoto]

Anyone out there hazard a guess on this problem?

I've been through all the service bulletins for a non-working Bosch Aquastar  (AQ 125 BO), and have done all the tests I can think of, but still the pilot light won't remain lit. Thermo-couple is putting out about 25 mVDC, right in spec with what it should be, and that leaves me with only the flue gas sensor and the electromagnet assembly as possible culprits. I'm not sure how the flue gas sensor is supposed to work, but as it's sitting on the exchanger coils, I'm guessing heat either opens or closes the contacts inside, thereby making or breaking the connection from the thermo-couple to the electromagnet assembly. This unit sits dormant all winter, and has given me trouble before when getting it ready for use in the spring. At this point, nothing I do seems to be able to keep the pilot light lit, including jumpering out the suspect components (ECO, flue gas sensor).

I'm just about ready to remove the unit and scrap it. Any ideas out there?

 

Thanks in advance!

Chas

[Cactus Bob]

sorry , i just saw you had already jumped the flue gas sensor , so i am out of ideas

this was an edit , sorry

Edited March 11, 2013 by Cactus Bob

[Budget Appliance Repair]

Have you done a basic continuity check on the safety magnet to make sure that it isn't open?

[jumptrout]

These might help.

http://www.bosch-climate.us/bosch-hot-water/aquastar-service-bulletins/

[chasimoto]

OK, fellow Samurai-ista's, here was my problem(s)...

 

First, an intermittent continuity problem in one of the leads going to the flue gas sensor. The wire connector under the shrink wrap was broken, but occasionally it would make contact and work for awhile. Hence, when I jumpered it out, that didn't work cause the break was in the wire connector. I should have noticed it being a bit too flexible, but hey, they looked skookum and I didn't even suspect that would have been it. I was all set to blame it on a failed electromagnet, but not so! 

 

I also seem to have a bad flue gas sensor which if wiggled, or even breathed on, will break continuity, so it needs to be replaced too. 

 

I've got it working now, but will still go ahead and replace the thermocouple as well as the flue gas sensor so all the components and connections will be new, just to get it back up to snuff. 

 

A thorny problem that I eventually figured out...Thanks for the replies, one and all.

 

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