Help with Hydronic Heating- main burners not kicking on

Discussion in 'HVAC Heating & Cooling' started by mookie3333, Apr 1, 2009.

  1. mookie3333

    mookie3333 New Member

    Messages:
    45
    Location:
    NYC
    I have a problem that needs to be solved soon, because my tenants have no heat!!! I was wondering if anyone knew what could be causing this problem. I have a HB Smith G200-W-3INT forced hot water heating system. The pump is constantly spinning, because the thermostat is calling for heat but the water that is circulating is cold water. When I switch off the system and switch back on, the pilot light comes on for about 45 seconds, and then shuts off after unsuccessfully trying to light either of the 2 main burners. Anyone know what could be causing this problem? Thanks in advance for any help!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,268
    Location:
    New England
    There are numerous safety interlocks on a boiler: low pressure switch, high overtemp switch, aquastat, flame sensor, (and maybe a flue pressure detector). There could be others. It sort of sounds like the system is not detecting the flame, and then does a safety shutdown. Often, it will sit for say 10-minutes or so to allow gas to dissipate, then try again. After a few tries, it gives up. There's often an indicator light that may be flashing a code. Course, you need to know where it is and what the code means.

    Sounds like you don't have the knowledge or skills to fix this, so it's time for a pro. There should be a wiring diagram somewhere pasted inside of the cover. If you can decipher the symbols, you should be able to follow the interlocks to see where it is open. If you are lucky, it could just be you need to clean the flame detector. You might need some new parts...hard to say without being there. The low-voltage interlock signals are usually 24vac, so if you can follow that path, see where it stops and that's the switch or interlock that isn't working. Now, it could be a bad device, or it could just be open because the thing it is measuring is out of tolerance...you'd need to know what it is measuring, and test for that. Sometimes, you can take it out and say put it in a pan of water on the stove (on say an aquastat) and see when it opens or closes as you monitor things with a themometer and a meter. It's not rocket science, but it can get complicated, especially deciphering the symbology on the diagram.
  3. mookie3333

    mookie3333 New Member

    Messages:
    45
    Location:
    NYC
    After some research, I figured it was more than likely the thermocouple. I shut down the boiler, opened up the covers, disconnected the pilot tube, and removed the pilot apparatus. My boiler doesn't have a normal "copper tube" thermocouple- What I saw instead was, right underneath the head of the pilot tube, a small cylindrical solid tube which is the same as a regular thermocouple, but instead of being attached to copper, it was protruding out of a bigger ceramic tube. At the end of this tube was an orange wire, which is the sparker. My question is, what type of apparatus is this called, and is that single wire able to produce the spark, as well as return a signal via thermocouple saying that the pilot light is on? My plan was to just replace the wire/ceramic tube/thermocouple, but of course all the local plumbing supply stores were closed! I'll have to do it this upcoming weekend, but I was just wondering if anyone knew what this was called and/or how it works. Thanks.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,268
    Location:
    New England
    That may not be a sparker...it may be a glow device...they apply power to it until it is red-hot, then turn on the gas. Once that happens, they measure the signal from it to determine if the flame actually came on. I had one like that on my old boiler.
  5. mookie3333

    mookie3333 New Member

    Messages:
    45
    Location:
    NYC
    That sounds about right, as the tip of it does turn red hot while sitting in the pilot light. Either way, it's been working flawlessly since I removed it, cleaned, and re-installed after realizing the plumbing supply was closed. Either way, if it happens again I'll just replace that whole apparatus. Very simple to replace, and it obviously was what was causing the problem. Now that was much better than calling in a boiler guy, who knows how much they would have charged to fix this! Thanks for your help, jadnashua.
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