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Short cycling

Hello I have a steam boiler that is short cycling I’ve had a plumber here and he said that it’s just how it work which I find hard to believe, what’s happening is it is reaching the cut off 5 psi fast and loosing it going down and in 2 min it’s back on again 
I have 3 radiators down stairs where the thermostat is one works good the other two take a long time 
if it’s 68 and I want 71 the thing turns on and off 20 times before it’s satisfied , then usually loses it quick I keep a electric heater  or the hot tv next to the thermostat so it dosent turn on and off so much, I don’t think there are enough radiators 2 were taken out and not replaced with the buy of the house ,
also in the extension part of the house they are turned off completely because they smell so bad,,but this dosent effect the man room where the thermostat is  the plumber told me I’m probaly loosing pressure somewhere but it’s ok cus that’s how it’s supposed to work it hits it’s max psi turns off and goes back on when it reaches bout 3 psi I said but is it short cycling turning on and off so much he said yea but that how it’s supposed to work, I no this can’t be normal what should I do? Will adding more radiators work. ? Also the gas lines are all brand new and pressure tested recently, so that’s not it . 


  • KC_Jones
    KC_Jones Member Posts: 5,745
    First, pressure is too high if it’s actually hitting 5 PSI.  Second, the pressure is a function of boiler size compared to the radiation and venting rate.  If someone removed radiators and you keep some turned off you are amplifying the problem of short cycling.  Turn all the rads on.  Do you know why the previous owner removed them?  What is heating those areas now?

    The next few steps to diagnose if you have to live with this or if it can be fixed will take some calculation and posting some pictures.  You need to measure all the radiators, develop an EDR for the system, then compare that to the EDR rating of the boiler.

    The next step will be main venting.  Start with how much you have currently, I’m going to guess not enough.  To verify how much you need will require measuring the length and pipe size of the mains.  With that information we can recommend how much moan venting you need.

    If the boiler is too grossly oversized, you will most likely only get “so good” on short cycling.

    For pictures post some of the boiler and piping above it, also post pictures of a typical radiator and it’s connections, and finally pictures of any main vents you have.

    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15