Viessmann B2HB 35 intermittent EE/E7 fault

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DevoThePlumber

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Viessmann B2HB installed in 2012 and heat exchanger was replaced on recall due to small hole in back of heat exchanger in march of 2023. I was not the initial installing contractor as our client purchased the home in august of 2023. I did a service on the unit in September of 2023 not knowing the heat exchanger issue and the boiler was due for a service, no trouble with faulting to this point. Replaced the ionization rod and the ignition electrode as part of the service. Come January of 2024 customer had to reset unit due to fault code EE, boiler ran for a week to ten days and the fault returned, went back and checked heat exchanger and flame current as well as gap on ignitor and flame rod, both were good. Noticed that the exhaust termination was at the same elevation as intake so fixed the exhaust with adding a gooseneck to bring the exhaust 15" higher than intake. With the code continuing to appear went back to check gas pressures/flame current/heat exchanger and vent length and fittings, all were in allowances even with adding the gooseneck. Boiler is continuing to fault intermittently with code EE and sometimes an E7 code, our local salesmen has suggested to replace the control console and gas valve which we did April 4 this past week, I also removed the rear refractory and the middle baffle plate to check the second pass heat exchanger, found some grit and particles back there which I cleaned and later heard from viessmann that was unnecessary as there is zero combustion that happens in that compartment but it clearly had some build up due to who knows what. Received an email from customer last night saying that it faulted again but this time he had to reset it 3 times before it would stay running. We are lost on what to do next and have already invested $2000 in parts on this unit plus the labor with no help or suggestion from viessmann on what the problem could be. Just wondering if anyone out there has had a similar issue and if you found a solution to the issue, any help would be appreciated!
 

Fitter30

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There is no mention of a flue analyzer with just a visual it's a guess. All manufacturers have in house service people that have full access to engineering. Wouldn't doubt that they have way to connect into the main board to record what is going on. I'd ask your sales person if they contacted the factory. Problems that you have need a new set of eyes and i don't care how much someone has work on a piece of equipment everyone needs help at some time.
 
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