I agree, you're right, there is potentially that effect, but the heat would have to last long enough to keep the thermostat above room temp so that it delays it coming on as the room drops. With thermostats there isn't enough mass there for the effect to last more than what? Ten, fifteen minutes? He wouldn't get his several hours, that's for sure.
I would agree that it's a thermistor, but how you couple that to a mass of any real consequuence in the typical modern thermostat, IDK. And it would have to be a heck of big mass to get hours of delay. I guess he could modify it, remove the thermistor, put it on wires, put it between a large mass like two bricks.....
OP here. If there's a "high limit" switch, it hasn't activated. (that would be on the aquastat, right?)
I don't really want the furnace cycling on/off repeatedly, just to maintain a specific setting on the thermostat by (say) +/- 1 degree, or even 2 degrees.
I don't mind a drop of 3-4 degrees (or even a bit more) between having it run.
What's really so hard to understand about that?
Having said that, I guess there really isn't a product on the market that can do this. If I was creative, I'd -build- one. Just to prove it could be done.
I may try using the DIP setting that's supposed to limit cycling to once per hour, and let it go at that.
What is hard to understand is what you don't want to cycle. Do you mean the burner on and off? The thermostat does not control that. Yes, the aquastat does.
The thermostat senses the need for heat. It turns on the circulator pump so hot water moves through the radiators. When warm enough, it stops the circulator as no more heat is needed.
Meantime, back on the boiler (not a furnace) the water temperature is sensed by the aquatstat and it turns the burner on and off to maintain the water in a given temperature range. High limit is usually about 190 degrees. You don't want to exceed that as the pump can cavitate.
You have to clarify what you want to get the best answer. Do you want the burner to cycle less? Do you not care about burner cycling but just want to limit the time period is runs in an hour?
Technical terms: Furnaces heat air. Boilers heat water. They have different controls.
Since he won't explain why he wants the system to run only once every three hours, maybe we should work the other way. Let's list reasons that one would not want the system to cycle *excessively".
1 - Each time a motor starts, there is some additional energy usage to get it going and some additional wear/stress.
2 - Each time the system starts/stops there will be some small amount of energy wasted as losses, for example heat left in the pipes in the loop inside walls, etc.
If a system was cycling on and off 10 times an hour, I can see the above being factors that would be of concern. But not if it cycles on and off two or three times, at that point the above issues become negligible. The systems are designed for that kind of usage over their normal lifespan. And with the latter cycle rate you can keep the temp of the house constant, which I would think would be far preferable to wide swings.
He also didn't answer the question of how he was achieving this with his old thermostat. Was he? I've never seen any residential type thermostat that could do what he wants.
Thanks for that information. This sounds almost like what I'm looking for.
I just want the furnace (boiler?) to come on when the temperature drops to a point I specify, and shut off when the temperature increases to a point that I specify.
I want it to "cycle", but not too often. Apparently a "normal" home thermostat can't be set up to behave this way. At least not with a "spread" as wide as what I would prefer.
Oddly enough, I don't recall this happening with my old thermostat (that had an old-style predictor/anticipator lever). But the new thermostat which has DIP switches instead of the anticipator doesn't seem to control the furnace as well the old one did.
It seems to turn it on, then shut it off prematurely. Also, it seems I have to set it considerably higher (desired temperature, top indicator) then the lower indicator (actual room temp?) indicates.
Maybe I just have a bad thermostat.
All this began because the furnace wasn't working properly. It wouldn't go through the ignition process reliably. The plumbing/heating guy cleaned the flame sensor and put on a fresh spark/sensor cable. He also replaced the thermostat with the one I have now.
It looked ok when he left, but then the ignition/startup problems began to recur. Furnace would try to start and you'd hear a "chattering" inside the intermittent control module (old Honeywell s86h). Sounded like there was a relay inside that wasn't holding. I could rap mildly on the side of the controller, and it would "catch", after which the furnace ran ok -- until the next startup, might do the same thing.
The module was 30 years old, and it was possible that it was failing. So, I replaced it myself with a new "universal" Honeywell module (checked documentation carefully so I knew it was the right replacement).
The furnace now starts reliably:
ignition spark on
pilot valve opens, pilot lights
flame rectification occurs, spark ends
main valve opens, burners light The LED light on the module shows normal operation.
But... again because of the thermostat, it seems to get shut down prematurely (if I set the thermostat to call for a "regular temperature", say 68 degrees).
IF I set the desired temp on the thermostat "way over" where it would be regularly set -- say to 85 degrees -- the furnace runs fine, UNTIL I set the thermostat back down to "way low" (say, 55 degrees). No overheating or thermal cut-off. It seems to run fine.
I can do this manually, but (of course!) would prefer it to run automatically without my intervention. But the new thermostat is giving me trouble.
I've set the internal DIP switches to 1 "CPH" (cycle per hour?), which isn't the recommended setting (it's the "recommended setting" that's giving me the problems!) but haven't had a chance to really observe the results yet.
I explained what began this entire problem in another post earlier this eve.
It was intially a -boiler problem- (ok, I'll call it a boiler, though it doesn't "boil" anything, just heats water to about 150 degrees). It wouldn't start up properly. Plumbing/heating guy cleaned the (combined) ignitor/sensor rod and replaced the spark cable. He also replaced original thermostat (which had old-style "anticipator" with a "lever" to adjust it) with new thermostat (has DIP switches to set cycle rate). Old thermostat was -at least- 40 years old, perhaps older.
At first, that seemed ok, but then later in the day the boiler had startup problems again. After investigating myself (and some reading and researching), it seemed obivous (to me) that the problem was located in the "intermittent module" (Honeywell s86h) that was 30 years old (came with the boiler in 1988). I replaced it with a new Honeywell universal module that had my old one "on the list of units it replaced".
After I did this, the boiler now starts up with a proper ignition sequence, there are no more problems in the startup sequence that I've observed.
The problem I have now looks to be that the thermostat doesn't seem to be controlling the boiler as it should. It shuts it off prematurely. Or at least it appears that way to me.
This DOES NOT seem to be a problem related to over-temperature or with the aquastat assembly. Here's why I believe this to be so:
If I set the thermostat "way up high" -- say, 85+ degrees -- the boiler starts and runs, and KEEPS RUNNING without any problems until I manually shut it down by turning the thermostat "way down" to, say, 55 degrees. Then the boiler just "clicks off" as it should.
If there were over-temp or other faults, wouldn't the aquastat take care of that, and force a shutdown? It DOES NOT do this. Aquastat is set (as far as I can tell) at about 182-183 degrees.
I just had it running a short while ago. I have the old thermostat sitting near the new one, so I can observe the room temperature on both. They are within 2 degrees of each other (indicated temperature).
The indicated temp was about 66 degrees. I set the thermostat to 71 or so. Boiler comes on and runs. Ran for about 30 minutes, then the thermostat shut it off. But indicated temperature reads 68 degrees. I'm just guessing at the discrepancies in the needles.
I've changed the DIP switch settings from the 3CPH setting to 1CPH. I'll see if that changes anything.
The thermostat I'm using is a Honeywell "round" model T87K1007.
I was using the DIP switch setting the manual recommended. That setting reads "High efficiency warm air (90%+), hot water, or heat pump (3CPH)"
That was causing problems -- boiler would start, run for a very few minutes, and shut off. The radiators wouldn't even begin to warm up. And it would repeat this at short intervals.
I changed the DIP switch setting to "Steam or gravity (1CPH)" to see if that would change things. And it DID -- it makes quite a difference. The boiler now starts, STAYS RUNNING until the radiators warm up, and then the thermostat shuts it off. The thermostat now keeps the boiler off until the radiators are cool, and then cycles again properly.
Seems much better. I won't say "that's it" yet. But "pretty close" to how things were running before I had problems a couple of weeks' back.
I should mention that my system isn't "steam". It's a gas furnace/boiler, hot water, cast iron radiators.
2-story house built in 1911, no insulation, plaster walls, original windows.
That's why I used the "gas hot water" setting first (it's what the plumbing/heating guy set it at, I guess he was going by the manual, too). But that setting clearly was wrong. At least for my system. The "steam" setting works much better.
I may investigate a programmable thermostat that allows the user to manually set the "temperature differential" (I think that's what it's called). The manual for this Lux unit:
formatting link
... says the swing setting can be programmed to 2.25 degrees F.
Question: If set to the 2.25 setting, does that mean 2.25 degrees
-below- the set temp and 2.25 -above it-, as well? That would be pretty close to "what I'm looking for".
J.Albert wrote: "should mention that my system isn't "steam". It's a gas furnace/boiler, hot water, cast iron radiators.
2-story house built in 1911, no insulation, plaster walls, original windows. "
My Gods Jim! Tighten up that draft stack you reside in: Insulate at least the attic, repair any cracks in the plaster walls and ceiling, and weatherstrip all exterior doors.
Then you can have your +- 2.25 degree temp swing using less of our precious resources.
Does the boiler run for domestic hot water also? That would account for running with no circulation.
After 100 years you'd think someone would be smart enough to insulate. You boiler will run much less once you do and it will pay for itself quickly, plus add comfort. Less run time, little temperature swing.
I think you have a boiler problem that you are trying to fix with a the rmostat. Not gonna work. Might as well just put an On-Off switch on the b oiler and run it manually until it breaks all the way.
When I grew up in Wisconsin, the thermostat controlled the boiler and t he circulating pump ran any time the boiler ran. That might not be the way yours worked. Radiators are slow to heat up and the room even slower, so there's no way our boiler cycled very often. In cold weather it never shut off and didn't quite keep up, but that's what sweaters and blankets are fo r.
When I lived in Germany the boiler maintained a loop temperature, zone valves opened for area demand, and each radiator had a thermostat on it. T he boiler loop temperature had a set back. If it was 0 F outside, it would run 160 F; if it was 60 F, it would run 120. Or something like that, I fo rget exactly. Of course the walls were a foot thick, masonry covered with plaster which totally eliminates infiltration, and triple pane windows.
Can't install insulation (at least the "blown in" kind). I also have original knob-and-tube wiring, and I believe that the recommendation is that blown-in insulation SHOULD NOT be used with K&T.
There is insulation in the attic -- directly under the shingles!
J.Albert wrote: "endation is that blown-in insulation SHOULD NOT be used with K&T. "
Understood. Not totally upon those details.
"There is insulation in the attic -- directly under the shingles! "
ERRRR!!
Unless there is finished living space in that attic, the insulation belongs in the attic FLOOR, not up between the rafters. The attic roof is open at the gutter sides, and serves as shelter against wind and precipitation.
In a home with unoccupied attic space, you insulate between the upstairs ceiling studs, not betw. rafters. Sheesh! Americans... No WONDER they consume billions of gallons of heating oil per season. Cain't even insoolayt properlee!
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