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Lochinvar high temp limit help

New to the site so hopefully this isnt the wrong way of doing this. I did search for this thread on the "wall" and found something similar, but it seemed to of fizzled out and no resolution was posted.

I have a Lochinvar model SBN1500 the is throwing a manual reset alarm for HX #2 high outlet temperature. Sometimes it will also throw a low airflow alarm for HX #2, but its kinda rare and usually right after the high temp limit alarm. It heats up to about 220 degrees before tripping. Also, on start up, HX 1 sounds fine, but HX 2 sounds like it has rocks in it tumbling around and the HX actually shakes. Looking in the sight glass, the burn pattern looks bad. No blue and it just looks like a bunch of hot spots across the burner.

Anyways, I started by swapping the outlet temperature sensors between HX #1 and #2, but the problem stayed with #2. HX #1 runs well with no problems, so a intake / exhaust being plugged can almost be ruled out being that they are common between the two HXs. I have confirmed the pumps are running, I have pulled and confirmed the strainer was clean, I removed the burner and cleaned and cleaned the HX but really didn't need it. I saw no rips in the burner and no damage to the HX. I called and talked with tech support and confirmed gas pressure.

Now my plan is to return with a combustion analyzer, share the results with tech support and see if they can help me adjust the inducer motor if need be. If that doesn't seem to fix the issue, I am thinking about pulling the unit apart as best as I can on the HX water inlet side with a hunch that maybe it is scaled up, causing a poor water flow and in turn high temperatures.

I think that's about everything. Any help with this matter is appreciated.


  • Jamie Hall
    Jamie Hall Member Posts: 22,050
    It does sound rather like you have a problem in HX2. What you may be hearing is localized flashing of steam on hot spots, then the steam collapsing -- sort of water hammer, but internal to the boiler. This could be bad circulation in that heat exchanger -- but it could also be the poor flame pattern which you mention.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • neilc
    neilc Member Posts: 2,501
    how long has the issue been occurring?
    and how is the circulator? and system piping?
    can we see a general distant picture of the boiler and all its piping around it
    known to beat dead horses
  • areese
    areese Member Posts: 2
    To Neilc, my company has just recently acquired this account so its hard to say how long, plus the boilers are only used in the cold weather times so they have just been started up for the season. Customer says that the high temp is new, but he has seen the low air flow in the past but the previous company could never give him an answer on it.
    piping and circulator appears to be okay, gain, my history with the building is limited. Im hoping to return maybe tomorrow or Friday and i will take some pictures.

    I also should have mentioned that HX1 was already replaced almost 2 years ago...

    To Jaimie, I agree with what you are saying about the improper flow and thats kinda where my head was at. I feel like it makes sense that the HX has a flow issue and that the noise and high temp are the symptoms.

    I am eager to get the combustion analyzer to this boiler and talk through it with tech support and hopefully tune this thing in a bit more and get to the bottom of this. Ill definitely get some pictures posted and keep this updated to hopefully help someone else.

    Thank you for the replies.
  • pedmec
    pedmec Member Posts: 804
    Sounds like you have two issue with the sync.

    1) Check the airflow accordion tubing for connections to the airboot. any rips or tears in it. Also make sure the airboot is installed correctly and not falling apart. I have seen the airboot installed wrong after cleaning a heat exchanger.

    2) Each heat exchanger has there own circulator. You either have trap air in the heat exchanger or dead circulator. If its the upper heat exchanger you most likely have air as both heat exchangers head to a welded tee fitting between each heat exchanger. Factory made manifold.

    also be careful with the gas piping to the inducer. Its another preformed piece of pipe going into the inducer. Because the bend wasn't correct the nozzle for the gas did not sit flush with the inducer. They use fine thread torx head machine screws to mount the nozzle to the inducer. The misalignment caused the threads to rip out of the inducer. It was drawing air between the gas nozzle and inducer allowing to much air in with the gas and not allowing ignition. Took a couple of hours to realize this. It was hard to notice.