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  • #31
    Re: My boiler is short cycling

    I think I have done all I can thanks to everyone's suggestion. As I stated before, I'm not trying to save a few bucks as a DIY'er. I just want to troubleshoot a bit so I have a clearer idea of the problem(s) so when the pro comes over, I can explain the problem(s) in more details. I'm in the IT support field, so troubleshooting is in my blood.

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    • #32
      Re: My boiler is short cycling

      That T8600D has some goofy quirks about it. Listen to NHMaster and pitch it. But if you want to verify that the stat is the problem: 1) turn off the power to the boiler 2) disconnect both wires from the stat and tie them together 3) turn the power back on and time it just like you did before.

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      • #33
        Re: My boiler is short cycling

        With that info, I agree about changing the thermostat and I really don't see the need for anything fancy. If someone will be at home all the time you'll most likely want a pretty much fixed constant temperature. It might be an idea to lower it a little at night but there's nothing nice about waking up to a cold house.

        Now please get a good tech to come by and give everything a careful checking over. Do replace the thermostat and keep it simple. There's nothing more angering than having it too hot or cold and not being able to change the settings of some darn Yaupo Schight fancy thermostat. With a simple manual type You and not It are in control. The fancy programmable ones are only worth it if you are away for a long time during the day and just can't bother to lower it some on the way out the door.

        There are far better and more effective ways to save energy.

        Ruddacguy has the idea about the thermostat test. You could try it and make note of the current connections. When reinstalling the thermostat or installing a new one, do have a small level handy. They need to be level.

        Note to tech:
        1) Replace the pressure relief valve and add a proper discharge pipe so it won't blast steam on/at people if it ever does blow. 2) Check limit switch and replace if needed. 3) Check low water shut down switch. Replace as needed.
        4) With the boiler shut down and the tech there, be sure to give the boiler a good flush. It would be a good time to totally drain your system, fill it up just a bit and drain the boiler again and again until it comes out clean. Then fill the system and work out air. Do this with the tech there and be sure everything works correctly before he leaves.

        A boiler full of mud/rust/sludge will not operate properly and it isn't safe. Get the crud out of it now.
        Be 1000% sure the boiler has been shut off and allowed some time to cool before you drain it and/or your system.
        Never drain out or fill a boiler that is fired or has just shut off. Never add water to a fired boiler. If it seems to be low, shut it off fast, allow cool down time and then and only then add water.
        Never, ever skimp on safety devices. If in doubt replace them.
        Last edited by Woussko; 03-12-2008, 09:28 PM.

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        • #34
          Re: My boiler is short cycling

          Before I put the 2 Mods in my house, I had a 120k single stage controlled by a T8600D. Whenever coming out of setback from 64 to 70, the furnace would cycle at about 68 degrees. I finally figured out that stat did that on purpose to prevent overshooting the setpoint. There may have been a way to turn that feature off, or adjust it, I dont remember. I suspect this feature may be partially malfunctioning on your stat.

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          • #35
            Re: My boiler is short cycling

            Originally posted by zuffy View Post
            I'm in the IT support field, so troubleshooting is in my blood.
            It occurs to me that it might be a syntax error in the flame roll out.

            Couldn't resist.
            Ruudac just suggested a great idea...a better version of Wousko's thermostat idea.
            Tie the two thermostat wires together from the boiler and see if it continues to short cycle while running.
            When you connect the two wires, you close the circuit like a thermostat does when it calls for heat.

            And, NHMasters gonna blow a gasket..at least let the guy know you're not ignoring him!

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            • #36
              Re: My boiler is short cycling

              I'm not trying to ignore NHMaster. I heard him loud and clear.

              I went to a vocational high school and took up electrical. Definitely top 5 student so I have a good understanding of electrical.

              If I am replacing the thermostat, it will be a fancy programmable one.
              1) I love gadget
              2) Like the 7 day programmable vs the 5-1-1 or 5-2. Even though I leave the house at a constant temperature 24/7, I do adjust base on outside temperature
              3) I don't expect my grandmom to be at the house for too long so I like to have the programmable option for future usage

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              • #37
                Re: My boiler is short cycling

                Zuffy

                Please don't be another Yaupo Schight with trouble making toys. For now PLEASE just get a simple basic thermostat your grandma can deal with. Once she is gone (sad times for sure) then you can buy the new micro processor model with loads of memory so you can set the temp hour by hour over a full month just as you like. It can have an outdoor temp and humidity sensor and even be able to sense when you're in bed sawing away or when no one is home. It will be equipped to flash a bright strobe if the temp inside runs below or above set limits. That way your neighbor will phone you that something is wrong. They really do have such models if you want to pay big $$$ and deal with programing the damn thing.

                I like to follow the old K I S S rule and keep Murphy under control.

                Give Rudd's test a try and please report what happens. Something is wrong where the boiler shut down only to restart after just a few minutes.

                The best thing you can do is get a good tech over, let him be alone with things and for him to check it totally out. Also get the sludge out of the bottom of the boiler. My bet is the whole system needs a good flushing but that's something for warmer weather rather than now.
                Last edited by Woussko; 03-13-2008, 12:01 AM.

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                • #38
                  Re: My boiler is short cycling

                  You know what. I still bet it's the thermostat, but looking at the picture I may have over looked something. Rare but possible. The boiler has an electronic damper on the flue. The boiler will not fire with the damper closed. There is a micro switch that allows the circut to close and fire the burner. If the damper, motor, or switch are F'd up, I have seen this also cause short cycling. Not common, very rare, but possible. To check. Pull both wires off the switch and bug them (tech. term) together. Manually open damper. See if it makes a difference.
                  sigpic

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                  • #39
                    Re: My boiler is short cycling

                    I am off today so here is another test log.

                    approx 10:25am - set thermostat from 68 to 69. boiler is firing

                    approx 10:35am - boiler stop firing. psi 3. thermostat still calling for heat

                    approx 10:36am - boiler fire back on. psi 0

                    approx 10:39am - boiler stop firing. psi 3. thermostat still calling for heat

                    approx 10:40am - boiler fire back on. psi 0

                    approx 10:43am - boiler stop firing. psi 3. thermostat stop calling for heat

                    approx 10:55am - took the thermostat off and checked the voltage from the 2 wires connected to R and W. Measured at 21.7V

                    approx 11:00am - power off boiler and then crossed the 2 wires to close the circuit

                    11:04am - power on the boiler. boiler is firing. psi 0

                    11:11am - boiler stop firing. psi 3. I can hear the water boiling inside the boiler

                    11:12am - boiler fire back on. psi gauge needle is just above the first mark

                    11:14am - boiler stop firing. psi 3. I can hear the water boiling inside the boiler

                    As for the damper. When the damper opens, I know the boiler is about to fire up and when the boiler stop firing, I know the damper will close. Doesn't sound like the damper is mulfunctioning.

                    I was reading the Honeywell thermostat installation manual again. It say to change the cph to 1 for gavity/steam system, which I did from 3 to 1.

                    Base on yesterday and today's log, it seem like the boiler stop firing once the psi gets to 3, regardless if the thermostat exist or not. Is that a good thing or bad thing?

                    Time to push my in-laws again to get that guy over to check my system.

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                    • #40
                      Re: My boiler is short cycling

                      A very good thing indeed. If fact 3psi is a bit high for residential but if it's working don't mess with it.
                      sigpic

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                      • #41
                        Re: My boiler is short cycling

                        Can I assume I don't seem to have a problem anymore? The air vents in the bathroom and master room are not hissing loudy anymore after the cleaning. Since changing the cph from the default 6 to 3 and then to 1 which is the correct setting for my steam system, the boiler have not been short cycling. The last time the boiler came on around 11:12am, it just came on at 3:23pm and stop at 3:43pm. The thermostat did not call for more heat.

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                        • #42
                          Re: My boiler is short cycling

                          You should not get a voltage reading across R and W. Its the same side of the 24 volt circuit. R, comes from the transformer to the stat, and W goes back to the gas valve but may go through a limit or 2 first. This would be like pulling a SPST light switch off the wall and measuring 120 volts between the 2 wires. Something is weird there.

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                          • #43
                            Re: My boiler is short cycling

                            It's only a 2 wires system for heat only. That is how it's connected in the thermostat. If those 2 wires touch to close the circuit, why shouldn't there be voltage. Am I missing something?

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                            • #44
                              Re: My boiler is short cycling

                              There should be around 24V at the thermostat.
                              sigpic

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                              • #45
                                Re: My boiler is short cycling

                                Checking the voltage across R and W at the stat is absolutely worthless. Depending on the gas valve and what type of safeties the system has, you might get a reading of zero, or a small voltage reading. Doing this, you are measuring between R, and C including the resistance of the entire gas valve circuit and any inline low voltage safeties. Checking the voltage between R and a good ground WILL tell you something worthwhile. This will tell you what the actual transformer voltage is. On most residential systems you will see around 27 volts. On residential systems installed in commercial buildings with 3 phase power I usually see around 21. On 3 phase commercial systems with multi-tap transformers I usually see around 30.

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