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Is my boiler short cycling?

My oil fired boiler gets up to heat fine. Typically takes 50-65 minutes to heat the house depending on the delta T. Water does not surge and does not need to be replenished to often. However after it has run for that initial time it will turn back on a minute latter for a minute or two, and does this two or three times, on then off, on then off. I had it overhauled in January and the contractor at 2 Rivers did a very thorough job cleaning all the parts of the boiler and adding an anti corrosion solution to the water.

When the boiler is running, the psi gauge reads just under 2 psi.

Any idea why it does this?


  • jpf321
    jpf321 Member Posts: 1,568
    most likely...

    most likely you are cycling based on your pressure controls .. and they seem to be set slightly high .. but within reason .. the consensus is to have the stardard pressuretrol set at 0.5psi with a differential of 1psi..read OFF at 1.5psi and back on at 0.5psi.

    it would seem that your thermostat is still calling for more heat but that your pressure tells the boiler to take a breather. is this the actual case? has your t-stat not been satisfied when the boiler starts with it's ON/OFF cycles?

    there are a variety of reasons why this could be the case possibilities include:

    -- uninsulated mains/returns/both

    -- improper venting (likely too slow) either mains or rads or both.

    -- you are recovering from a deep setback (most recommendations suggest a setback of no more than 5degF)

    -- your windows are open (or you do not have the proper amount of radiation for your expected heat-loss)

    -- stuck/dirty/painted-over rad vents (causing slow venting as noted above)

    -- partially/fully closed down radiator inlet valves (these should be fully open at all times)

    -- i'm sure i'm missing several things .. but here are a few places to begin with..

    i'm sure that the tempting thing to do is to raise the pressure setting .. THIS WOULD BE WRONG. If anything, see if you can bring the pressure down to 0.5psi and 1psi-diff .. and then troubleshoot why you are cycling on pressure.

    less likely is that you are cycling based on Low Water .. do you see sufficient water in the gauge when you begin the on/off cycles?

    let us know.
    1-pipe Homeowner - Queens, NYC

    NEW: SlantFin Intrepid TR-30 + Tankless + Riello 40-F5 @ 0.85gph | OLD: Fitzgibbons 402 boiler + Beckett "SR" Oil Gun @ 1.75gph

    installed: 0-20oz/si gauge | vaporstat | hour-meter | gortons on all rads | 1pc G#2 + 1pc G#1 on each of 2 mains

    Connected EDR load: 371 sf venting load: 2.95cfm vent capacity: 4.62cfm
    my NEW system pics | my OLD system pics
  • Steve_175
    Steve_175 Member Posts: 238
    More info

    Thanks for the reply JP.

    The mains and returns are all insulated.

    All vents on rads work great.

    New Gorton mains on the boiler a year ago.

    Rad valves fully open.

    Plenty of water in the gauge before and after the boiler runs.

    BTW I posted some pictures but do not see them here.
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