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How can we prevent boiler from short cycling?

Hi all,

Looking for some extra tips or troubleshooting when it seems that my boiler is short cycling. Thermostat will click on for approximately 3 minutes or so before turning off. We've changed all of the vents on our radiators to vari-vents, which has helped in achieving a more even heating of my 1931 tudor, but I still get a quick on/off out of the thermostat. Thermostat is in a central location, away from other radiators so I'm thinking something my be off with it. Any suggestions?


  • Jamie HallJamie Hall Posts: 11,466Member
    If it's the thermostat that's clicking on and off -- it's the thermostat. If it's the type with an anticipator, it could be that it is just very badly misadjusted. Otherwise, may I suggest a new thermostat? They're not all that expensive, provided you don't carried away with gadgets and frills...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • JUGHNEJUGHNE Posts: 6,224Member
    Are you sure the thermostat is actually turning off the boiler or is the pressure switch on the boiler doing the switch off? If you turn the t-stat all the way up to max, does the boiler stay on? If not than probably the pressure control on boiler is in charge.
    Did you just change out the T-stat?
  • jimvansjimvans Posts: 5Member
    Thermostat is definitely shutting down the boiler. Have been considering a new thermostat for a while now, so recommendations would be welcome. Unsure of the age of the thermostat, but I've attached a photo. It is a Honeywell thermostat, but I can't tell the model.
  • FredFred Posts: 8,105Member
    Honeywell makes a good thermostat, just make sure the one you buy has a setting for Steam (1 CPH) hot water (2CPH) and many will have 3, 4 and 5 CPH's as well. Some skip the 2 CPH for some reason and you definitely want that option if you decide you want to try 2 Cycles per hour to even the room temps out a little more than 1 CPH will do. I have the Honeywell 7000 series programable thermostat.
  • KC_JonesKC_Jones Posts: 4,281Member
    Do you know what the CPH setting is currently? In the manual go to page 17-18 and make sure you are set to steam heat depending on which one you have you want either function 5 or 6 set to 1. If it is set to anything else that could be the problem. If it is already set to 1 I would be inclined to agree with the above the thermostat has a problem and might need replaced.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • jimvansjimvans Posts: 5Member
    Thanks everyone. I just found the manual and went through the settings. Turns out I was at 5CPH. I've now set it to 1CPH. Obviously, I'll have to wait and see how this affects things. Really appreciate the help! I'll report back if this doesn't seem to do the trick.
  • FredFred Posts: 8,105Member
    That will do the trick!
  • ChrisJChrisJ Posts: 10,244Member
    You're going to find that works much better on 1 CPH than on 5.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Jimbo_5Jimbo_5 Posts: 202Member
    Did the old "round" thermostats have CPH? What is the advantage of CPH?
  • Mark NMark N Posts: 1,068Member
    On the Honeywell T87 you set the cycle rate by the proper setting of the anticipator. With an electronic thermostat you skip the anticipator and set the cycle rate.
  • Mark NMark N Posts: 1,068Member
    edited February 2015
    If you use a Honeywell thermostat and don't set the proper cycle rate you heating system will most likely perform unsatisfactorily. The installation instruction cover how to set it.
  • Jimbo_5Jimbo_5 Posts: 202Member
    My problem is the CPH causing the boiler to fire and run for 10 minutes, thus running very low supply & return water temps in that 10 minutes. I am worried about condensating due to low temps. Is there any advantage to digital thermostats? Neither Well McLain nor Honeywell has an answer.
  • FredFred Posts: 8,105Member
    Jimbo said:

    My problem is the CPH causing the boiler to fire and run for 10 minutes, thus running very low supply & return water temps in that 10 minutes. I am worried about condensating due to low temps. Is there any advantage to digital thermostats? Neither Well McLain nor Honeywell has an answer.

    If you get a thermostat, like a Honeywell, you can select the number of cycles from one per hour up to five per hour. Just make sure to read the specs on the thermostat you intend to purchase. Some of them, even some Honeywell models will not have the 2 CPH option programable on them (the model I have, a series 7000 does have 2CPH and it is defined as being for Hot water heat, which it sounds like you may have???)
  • jimvansjimvans Posts: 5Member
    It's been a few days since I changed from my thermostat being at 5 CPH, down to 1. I've seen a huge difference in the way my home heats. Getting to the setting to change this is not very intuitive, but extremely simple once you know how. I'm still considering a new thermostat, as I'd like to have more features. We do not have central air and are considering adding a split-system AC unit in our finished attic. I've seen some compatibility with Honeywell's RedLink system and Mitsubishi split system units, so I'm curious if anyone has any experience with the RedLink thermostats?
  • icesailoricesailor Posts: 7,265Member
    Keep the existing Honeywell you have for your heat. If you put in the AC for other areas, they come with their own thermostats. Let those T-States do their job.

    Unless you want to try to make that thermostat do another different job, and avoid a second thermostat, leave the old one alone. It works now. Just remember what a PITA you had until you re-set the CPH setting. Try to make the old Honeywell do two, and you will be resetting the CPH switch twice per year.

    Wisely, with a steam system, you are running that T-Stat on "Hold" which over rides the clock feature. Steam systems seem to be happiest when left alone and to run at their own speeds.
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