Honeywell CT3600 Thermostat---Cycle Setting Question

Fred

First, you are right, it's not just guys! Now if we could combine this site with a "Match.com" we might have a winner. To your other point, if the thermostat is set for 1CPH, the boiler should not cycle on more than once an hour unless it shut down on pressure or low water before the Thermostat was satisfied. I'd look at the Thermostat settings and double check that it is, in fact, set for 1 CPH. Maybe something is wrong with it???

Captain Who

Well I don't have a Honeywell but my White Rodgers which is currently set at the 0.6 F anticipator setting (only other option is 1.2 F !), will do a number of short test cycles in a row, apparently so as not to overshoot the mark too much. I know that when it first starts this series of short firings (can be only 3 to 4 mins on time sometimes), when it first shuts off, there is NO WAY that the thermostat has felt any temp rise in the room yet, as the steam has just barely entered the rads at that point. You'd think that it would've learned by now that it is OK to fire for longer but that's just the way the algorithm inside is written apparently.

Captain Who

PS: unless it is extremely sensitive to slight increase in radiant energy of the radiator from across the room. I doubt it but an experiment might be to cover the front of thermostat with some heavy duty aluminum foil already at room temp (without blocking the vents) the next time it starts one of those series of firings, and see if it makes any difference in the duration of the firing.

Fred

Are you guys sure you don't have a short in the Low Voltage wiring or the Thermostat or a control on the boiler? I can see that happening on a mercury switch that may be just tetering on the edge but not on an electronic device.

vaporvac

Well, I don't think so. A VERY compentent boiler man hooked up my burners and did the analysis. I did the Tstat, so it could be user error, but I did check on the voltage meter before hooking it all up. Tell me more.

Captain Who

Fred said:

First, you are right, it's not just guys! Now if we could combine this site with a "Match.com" we might have a winner.

Good idea lol.

Fred said:

To your other point, if the thermostat is set for 1CPH, the boiler should not cycle on more than once an hour unless it shut down on pressure or low water before the Thermostat was satisfied. I'd look at the Thermostat settings and double check that it is, in fact, set for 1 CPH. Maybe something is wrong with it???

I'm not so sure. If I understand correctly it could run a great deal longer than that, if need be to satisfy the setpoint, like for example when recovering from a setback or if a sudden heat loss occurred in the building like someone opening all the windows. Once the setpoint is reached though, it will then have a lockout period of 30 min (for the 1CPH setting) where it will under NO CIRCUMSTANCES turn on again, even if something happened suddenly to drop the temp of the house down to 40 degrees, for an extreme example. Then it might have to fire for another couple hours straight before it reaches the setpoint again. Lather Rinse Repeat.

Captain Who

Sorry maybe I misunderstood what you were saying Fred.

Fred

If the thermostat is set for 1CPH, it will run for ever (theoretically) if the thermostat is not satisfied. Once satisfied, it should not come back on for an hour after the thermostat was last satisfied (1 hour, not 30 minutes. If it is locked-out for only 30 minutes, then that would be 2CPH).
I believe any change to the thermostat setting (like raising the temp requirement from 70 degrees to 72 degrees) resets the clock at that point and the boiler will come on immediately and stay on until the new temp is achieved and then the lockout occurs at the point of thermostat satisfaction.
What i don't know is (as in your example) a drastic or sudden change in room temperature say 5 degrees or more (maybe only just a couple degrees) kicks some sort of software default into play that would override the CPH clock until the thermostat is again satisfied. It would make sense that that would be the case but I have never tested that and don't know if I want to just to see what happens. I'm sure there is some rudmentry logic in the Thermostat that says "If this happens, then do this".

Captain Who

I agree except that according to the other thread I read which I gave the link for they said that the lockout would be 30 min, which makes sense to me because a 1 cycle per hour setting (CPH =1) would theoretically be 30 mins on followed by 30 mins off. 30 mins + 30 mins = 1 hour cycle duration.

Fred

Not so. It is 1 hour after the thermostat was last satisfied. Many times a boiler will only run 10 or 15 minutes. 30 minutes later would be 40 or 45 mintes total and 2 cycles per hour. I do know for a fact that my boiler will not kick back on for 1 hour after the last boiler shutdown on a satisfied thermostat. Like clockwork (pun intended). It is a rolling one hour from last boiler shutdown to next boiler startup (if the Thermostat calls for heat or at any time after that 1 hour period if it should happen the Thermostat doesn't call for heat at that specific hour.

Captain Who

Well I certainly won't argue with your actual results. It is interesting.

Here's the info I got in the other thread and what I was referring to:

"http://www.heatinghelp.com/forum-thread/127201/How-does-a-digital-thermostat-really-work-inside

The last few postings go into a lot of detail on how the cycle rate program operates on a digital thermostat.

Basically, the thermostat measures the room temp and compares it to the setpoint. Assume the room temp drops to the lower threshold ( setpoint minus differential ) for a call for heat and fires the boiler. When the room reaches some predetermined temp approaching setpoint, it initiates the timing cycle. For 1 CPH the timing interval would be 30 minutes on, 30 minutes off. So the thermostat stops the call for heat and then checks again in 30 minutes to see if setpoint has been reached. If it has, it waits to fire the boiler again until the low temp call for heat threshold is reached. If setpoint has not been reached, it fires the boiler again and repeats the cycle. By stopping firing before setpoint is reached, and then waiting half the cycle time before again checking, the thermostat prevents overshoot in a similar manner as the anticipator did on analog thermostats."

In my mind when the poster above says setpoint "reached" or "not reached", they are referring to "reached" = temp between lower threshold and setpoint, and "not reached" = temp at or below lower threshold.

Captain Who

correction: "reached" = temp greater than lower threshold, ie. could be between lower threshold and setpoint, could be greater than setpoint even.

PMJ

I really think you guys (and gals) would really like messing around with a unit where you write your own code instead of trying to figure out the fixed logic inside these other ones. Less than $100 too. No limit to what you can come up with to make your boiler do what you want when you want it to. You just keep tweaking the code. Just sayin.

Fred

I read that thread and it seems to me that most of what was said was more pertinent to the software in that thermostat designed for Forced air and not what happens for Steam. I suspect when you initilly program the number of cycles per hour, you are essentially telling the thermostat which software (actually firmware) parameters to use. 1CPH, steam perameter, 1 Cycle per hour, rolling hour after tstat was last satisfed and any other "if this happens, do this senarios pertinent to steam , 2CPH, Hot water scheme, 3CPH, 4CPH, 5CPH etc., what ever schemes are designed into those senarios. In the example given where on a 6CPH model, what was said was 5 minutes running at which time the Tstat does essentially a status check, not that it actually shuts down (although it may depending on that status). On forced air, a "shut down is not like a boiler shutdown. With forced air theburner is frequently shut down based on an upper limit switch on the heat exchanger and the furnace fan continues to run until the heat exchanger gets down to a "Low limit" or a timed delay even after the burner has shut down so the homeowner doesn't necessarily know that the burner shut down for a quick status check. On a Steam boiler it is obvious when the burner shuts down. With hot water, I don't know if the circulator pump shuts down during a status check or not. I suspect not as it is probably on a delay of some type as well.
Having said all that, I can assure you, at least with the Honeywell RTH-7000 series, the boiler is shut down for 1 hour after the thermostat was last satisfied except when other defaults apply. I can't speak to White Rogers or any other brands/models. Certainly, even with other brands, I can't imagine they would kick the boiler on for a minute or two as part of any status check. The Thermostat basically is sleep until a temperature drop of somewhere around .5 degree or another default action awakens it.

Fred

MarkS said:

I read somewhere that people can't detect room temperature change narrower than 1.8 deg F. I think whoever wrote that clearly wasn't married.

Funny!

Fred

PMJ said:

I really think you guys (and gals) would really like messing around with a unit where you write your own code instead of trying to figure out the fixed logic inside these other ones. Less than $100 too. No limit to what you can come up with to make your boiler do what you want when you want it to. You just keep tweaking the code. Just sayin.

It would be great if there were a thermostat out there that had some type of "Open source" firmware coding that would let you select and/or create specific functionality and load it onto a chip in the Thermostat, maybe using a PC as the development/input vehicle.

PMJ

I use a PLC with a standard programmable thermostat as an input and the burner circuit as the output.

Fred

That is probably a bit too complicated for the average homeowner. I'm thinking something that you use a USB port on PC, load a program on the PC that has virtually all possible options that a person can pick and choose from, have the app tell the user if any of his/her selections conflict with other selections and when done, load it into the Thermostat. That would probably satisfy 95% of the heating market and the remaining 5% with the know how could code specific functionality and still let the app identify and potential conflicts. I want all of that for $129.00 (I know somebody is going to say "we don't discuss pricing here" but this is just theoretical. Aren't PLC set-ups kind of expensive and don't you basically have a PC dedicated to that functionality100% of the time?

PMJ

Simple PLCs have become cheaper than thermostats that have any special functions at all. Software is free. They are 1000 times more reliable than PCs and can be left running your boiler without worry that they will stop. No, the PLC is not for the average homeowner. But then I'm not thinking this group is average. For anyone who does like/want to tinker with changing run times vs call times or anything else you can dream up the PLC offers unlimited possibilities. They can appear intimidating at first but really aren't that tough to learn. The cost is so low I just thought to suggest some people here might want to look at it.

Captain Who

@PMJ - I for one am very interested. Can you point us to some links to start learning more about how to do it?

KC_Jones

I used to work for an electric utility and we used PLC's all the time in control systems for the power grid. I agree about how stable they are. Probably the most rock solid piece of equipment we put on the system.

PMJ

Captain Who said:

@PMJ - I for one am very interested. Can you point us to some links to start learning more about how to do it?

Go to factorymation.com and click on the link to programmable controllers. Lots of info there.

SWEI

PMJ said:

I think all systems have about 30% more boiler than is needed once the delivery piping is heated up. The piping doesn't cool down enough to talk about in 10 min if it is insulated properly.

Which is exactly why two stage firing should be a standard option, available on every steam and hot water boiler.

PMJ

SWEI said:

PMJ said:

I think all systems have about 30% more boiler than is needed once the delivery piping is heated up. The piping doesn't cool down enough to talk about in 10 min if it is insulated properly.

Which is exactly why two stage firing should be a standard option, available on every steam and hot water boiler.

Agreed. Without it there does seem to be a rather large hole in the control picture of the standard setup. I find it a bit shocking that some of the old coal systems had modulation and we don't even get 2 speeds.

Fred

The PLC looks like a great option for anyone who isn't satisfied with the limited control available on a standard thermostat alone. I'm wondering why (or maybe when?) Boiler manufacturers might integrate them into the boiler configuration to help control cycles, cycle duration, burner modulation/staging, maintenance management, diagnostics, water management. (At the residential level of course. Some or all of this may already be in place in the industrial market). Maybe overkill in the residential market?
Thanks for the insight.

Fred

vaporvac said:

Well, I don't think so. A VERY compentent boiler man hooked up my burners and did the analysis. I did the Tstat, so it could be user error, but I did check on the voltage meter before hooking it all up. Tell me more.

Hi Vaporvac. I don't know how your tstat is set up but my comment was related to the fact that a thermostat is basically sleep until a programed or default function wakes it up. The one function that would wake it up is a call for heat (sensor trips because the temperature is outside the "acceptable/normal range). The question I can't answer is what other functions you may have programed into your thermostat but under normal default settings, a Thermostat won't wake up, start the boiler for a minute and before any heat is generated, shut it down unless it thinks it needs to call for heat. If that's the case, is there any programable adjustment to change the sensitivity of the temperature range between "within range- no call" and "outside of range - call for heat" ?

vaporvac

Hi Fred. I didn't take offence. While I'm SURE the is burners are hooked up correctly, I only THINK that the Tstat is and your point about a loose wire is a good one. It does come on and off which was an improvement over running up and down stairs to switch the burners!
When I originally posted about this , it was pointed out that the temp swing is fairly small. http://forum.heatinghelp.com/discussion/152167/honeywell-wifi-tstat-problems-any-solution#latest
I reprogrammed my cycles just in case they were wrong (it was really hard getting it to the correct number the first time), so I'll see how the cycling goes today.
SO, to clarify: if the temp drops after the 1 CPH will it start back up to fulfill the temp requirement or wait until an hour passes?
Update: Just went off 10 minutes ago and has started back up. I'm tracking the time and going to check the pressure.

Fred

On mine, (again a model Honeywell RTH - 7000 series) it is off for an hour (give or take 3 to 5 minutes) after the Thermostat was last satisfied. If you have your Thermostat programed correctly for 1CPH, it sounds to me like some other control may be coming into play. Do you have an auto water feed on your system? Is it a Cyclegaurd? They will shut a boiler down, wait about 10 minutes and then restart the boiler if the Thermostat wasn't satisfied on the last call for heat. Do you have an outdoor reset? I'm not sure how/if that may override the cycle setting on the thermostat. I'm assumming thee boiler isn't short cycling on pressure (off for 10 minutes is longer than a typical pressure short cycle)In any case if none of those things come into play, it definitely should not come back on in 10 minutes. It sounds like the thermostat is cycling for forced air or there is a short somewhere in the low voltage line/components.
-I once had a forced air furnace thwould kick on and over-shoot the thermostat setting by 10 to 20 degrees. After checking all the controls, my last resort was to replace the wiring. As I was doing that, I found a trim nail was driven into the thermostat wiring about two feet from the thermostat and when a person walked on a specific area of the floor in that room, it applied just enough pressure to short that wire. walk back across the floor, break the short. Amazing but resolved!

Captain Who

The CycleGuard only tests for 90 secs. If you have the "SmartCycle" feature enabled it will only shut down the burner to test if it has been 10 mins since the burner last fired up. Everytime the burner fires up, it re-initializes that timer at zero.

Mark N

Vaporvac maybe your thermostat is just defective.

vaporvac

That could be. I'm calling HW Monday to see what I should be seeing when resetting the CPH. Currently when I press the two buttons together to reset it, it shows me the default setting, so I don't know if that's just for the reset, or if somehow, it keeps going back to the default.
I don't have auto refill ore odr (I wish), and run in a vacuum unless coming back from a setback. (In that case, it runs until the temp is satisfied... no cycling), but I'm leaning toward a short. We replaced part of the line as it had broken. It's possible there's another small break in the closet that could be jiggled when hanging coats. Unless it's the Tstat itself.
What does yours show, Fred when you go to change the CPH: what you had it set for or the default? (I know that's a lot to ask, but I'm stymied).
P.S. It comes on when it's just a fraction off of the set point.

Fred

The default setting from the factory is 5CPH for forced air. To set my CPH, I press the system botton, release it then press and hold the Fan button until the screen changes.The first screen is for year, month and date setting, to go to the next programable function, press "Next" the next screen is "System Type" use the up or down key to select your system type as described in your installation guide, press next and you get the "Heating Cycle Rate" press "1" for gas/oil steam or gravity systems. Press done and the programing should be set (On yours I'm sure there re other settings for WiFi and whatever but if those are working ok, just press "Done after the "Cycle Rate" screen and those will be saved as they are.

My CPH screen shows what I have it set for which is "1"