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Boiler cycles on/off continuously

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aprot
aprot Member Posts: 4
in Gas Heating
I have a 5 yr old Bradford white gas boiler for heat and hot water. The heat exchanger was clanking loud so I replaced the pump and purged air. Running quite again but the boiler doesn’t stay in the run position. It cycles continuously. Each cycle lasts about a minute and a half but is only in run position for about 30 seconds or less. Is this normal?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,284
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    No. But there is a multitude of possible causes... Did it do this before you replaced the pump?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • aprot
    aprot Member Posts: 4
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    Yes it was. At least when I noticed the sound in the heat exchanger. Heat exchanger is back to making noise so the unit is off now. The temp never gets above 140.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,520
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    @aprot

    pictures
  • coby
    coby Member Posts: 17
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    Is new pump working and what is high limit set at? Also since you bled system did you open all the valves up you may have closed.
  • aprot
    aprot Member Posts: 4
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    All valves are open. I think the high limit is 190. I replaced the expansion tank after noticing a slow leak. Fired it up and heated enough for a couple showers and warm the house up. In the morning it was short cycling again and had air in the heat exchanger. I’ve been reading that the flame sensor could be causing the short cycling. I’ll try and replace that. What would be causing air in the heat exchanger?
  • SuperTech
    SuperTech Member Posts: 2,160
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    > @aprot said:
    > All valves are open. I think the high limit is 190. I replaced the expansion tank after noticing a slow leak. Fired it up and heated enough for a couple showers and warm the house up. In the morning it was short cycling again and had air in the heat exchanger. I’ve been reading that the flame sensor could be causing the short cycling. I’ll try and replace that. What would be causing air in the heat exchanger?

    It sounds like it was not properly purged after the expansion tank replacement.

    Purge the system, make sure your air eliminator is working. 1/8" air vents typically should be replaced when the tank was replaced
  • aprot
    aprot Member Posts: 4
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    Where can I find the air vents and how do I properly purge?
  • coby
    coby Member Posts: 17
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    So you have a trap in the back of the boiler on the bottom. That needs to be cleaned. For that take out and flush water through until it comes out both sides. Noted when you take out or off the black tube on the bottom of the heat exchanger ( it connect's heat exchanger to trap) you will get a bit of water if it's plugged, be prepared. That is probably the water in the heat exchanger noise and maybe part of your problem. Also take out and clean the flame sensor and spark electodes try this before replacing them, though not a bad idea to replace every 5 or so years. The 2 red wires in the front lead to them 2 screws on each, make sure you put them back in the correct spot ( do 1 at a time). These things should get you going, but recommend spending the money on a Qualified Techinician to come out and maintain every year for best results. Goodluck let us know how it turned out. P.S. from the picture could not see air vent, but typically on top of air seperator where the expansion tank is screwed into and also should have one of top of heat exchanger of that unit.

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