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Ultra 105 series 2 B 30 error only on DHW call

Yesterday had our boiler serviced by reputable local firm. Previous contractor no longer available. (maybe he knew some tricks) When the boiler maintenance was complete, the tech called me down to show me that the boiler was throwing B30 code. He then showed me that there is no check valve in the return line from the water heater and pointed out that one was needed according to the boiler install manual. He blamed this but I told him we'd been running fine with DHW calls for months without the hydronic heat being on. He left without resolving and I have been monitoring the system.

Findings: Running hydronic heat, single zone, which cycles the boiler return pump on, will keep the boiler temp down at 108 when the DHW is also cycling. Now if I stop the zone by turning down thermostat, the return pump stops, but the DHW continues to call for heat and its pump is running. The problem occurs as soon as the boiler temp hits 110/112. The B30 error immediately pops up and the boiler stops firing. Temp must fall again before DHW cycle will begin, but it will still fail again at 110/112 with B30 code. Soft lockout and boiler cools off again. After 5 minutes, at 98, kicks back on for DHW and then cuts out with B30 again in a couple minutes at 112. This constant cycling is NOT normal. And my hot water will never reach the thermostat setting on the water heater at this rate.

Problem is, before this service I had to fix the return temp sensor in June and so I documented boiler running just for DHW cycle (first digit of 4 on LED, 3 is for heat). I have pictures showing that the boiler was heating up to 168 and never throwing a B30.

The tech that serviced the boiler yesterday was using standard maintenance kit, gaskets, ignitor, etc. He cleaned venturi, heat exchanger, burner. But he is adamant that his maintenance did not cause this new problem and that the check valve missing in water heater return line is the real culprit. Of course, I know the system has been running without that check valve since it was installed in 2007.

What am I missing here? Is there some cutoff for the DHW or boiler that has defaulted to 112?


  • delaneybill
    delaneybill Member Posts: 4
    I called Weil McLain directly and did my best to present this problem as I have documented it above. But they quickly cut me off and told me that my issue MUST be a water flow issue in the hot water side. I banged heads with them for a bit but in the end they directed me back to the contractor and said that a 15 yr old installed system probably is not having this problem due to a missing check valve. And that it MUST be a water flow issue. Will update this post after I get the contractor back out.
    HVACNUT Member Posts: 4,654
    You've gone through these steps?
  • delaneybill
    delaneybill Member Posts: 4
    Took me all morning just to come back to the same old return temp sensor problem. Only this time it was trickier because instead of giving me a hard lockout code, it was just reporting a much lower temp. I realized something was up as soon as I checked the info mode and noted that my return temp was like 30 degrees below ambient. Impossible!
    So, back to unplugging and cleaning, but I really need to replace the sensor soon since the corrosion is so bad. For now, just happy to have it running again.
    I will be kind to the contractor as I want to do more business with them. But I did mention the sensor and showed the tech I had a replacement. A little more attention to detail and this lengthy troubleshooting session could have been avoided.
  • delaneybill
    delaneybill Member Posts: 4
    Thanks HVACNUT. I just saw your reply. It was in the list for b30 error. :blush: