Boilers groaning

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Thom Walsh

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Hi to all,
I installed five Unical modulating condensing boilers on my street last year. You probably haven't heard of Unical. They are popular in Europe but don't have a big presence in the USA. Anyway I talked my neighbors into purchasing these boilers together from the only distributor in the USA , located in Iowa. I am a retired technology/vocational teacher. I did the research on condensing boilers and hydronic systems and a former student of mine (a highly qualified HVAC tech) actually did the installs.
The boilers operate and function great. But two of my neighbors boilers will, on high fire intermittently growl. It sounds like a muted fog horn. The tech has been back to check the parameters on high and low fire and everything checks out. It doesn't happen when he is there (of course!). I also noticed in the installation manual it asks for a static gas pressure of 7.0 W.C. I called the gas company to check the regulators and pressure. They swapped out a defective regulator on one and raised the pressure to 8.0 W.C. Eureka! Two days went by and no noise. Saturday night my wife yells to me that the boiler is groaning again. Has anyone encountered this problem before? I could deal with this if it was my boiler but I feel responsible since I talked everyone into these boilers. By the way, everyone is very impressed with the savings compared to our old oil burners.
Thanks to all for any suggestions- Thom Walsh
 

Thom Walsh

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Support for Unical means getting in touch with the rep in Iowa. He never calls me and will only communicate by email. Probably not the wisest decision to buy long distance without a good support network. They do seem like good boilers though. I live on Long Island, NY.
 

Tom Sawyer

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I think you may have a problem with the incoming gas pressure fluctuation. The utility company should be able to help you
 

Tom Sawyer

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I would have thought that too but he said it went away when the swapped a regulator. I'm guessing the street pressure is varying a lot.
 

Thom Walsh

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It may be a gas pressure issue, but more likely a water flow problem. You will have send a picture of the near-piping.
I'll send a picture of mine. It is pretty representative. Mine has more zones and copper headers but thats it. My house is directly across from the groaning boiler and my regulator is set to a static 7.0 W.C.
Thanks Guys
 

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BadgerBoilerMN

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But then it came back.

A combustion analyzer is a must on combustion boilers, but flow control can't be overlooked.

Another good argument for local distributors and support. Even when I design a system, out of state or out of country, I start with "available" boilers and know the companies before I recommend them.
 

Thom Walsh

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Good point. My installer is going to check combustion again. Water flow doesn't seem to be an issue.
 

Tom Sawyer

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A combustion analyzer that reads continually will expose a gas pressure issue as the CO or O2 level will change when the pressure does.
 
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