Is there a device to STOP oil burner short cycling?

 
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Post by SMITTY » Thu. May. 04, 2023 10:47 am

Back in the day I remember Beckett made something called the "Heat Manager" - an electronic magic box that was supposed to cut down on short cycling. It had mixed reviews - some called it a POS, while others loved it. Seems they don't make it anymore, so I guess the former was true, lol.

Anyway, my oil burner has been plagued with this short cycling issue for DECADES. It's just the nature of the system - 2 zone valves, plus a hot water zone - one circulator for the 2 heating zones. So if the water temp is below high limit and the differential, the boiler will fire any time there's a call for heat. Yeah .. that's what it's supposed to do .. BUT, when there's a light heating load, the 2 zones might call within seconds of each other, and drop out just as fast. That makes the burner light for 5 seconds, shut off, then refire seconds later and shut off again. Sometimes up to 3x this cycle will repeat.

This has been beating the *censored* out of this burner. I'm shocked the motor still works! Would've got 50 years out of it if not for the short cycling, though. Not to mention the waste of expensive heating oil. Since I plug in my stoker to the same aquastat power supply, it does happen on coal, too.

I'm thinking some kind of adjustable time-delay device in series with burner motor power is the answer for this. What say you?


 
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Post by franco b » Thu. May. 04, 2023 12:08 pm

If the thermostats have heat anticipation, then lower that setting all the way, and see what happens.

 
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Post by SMITTY » Thu. May. 04, 2023 12:14 pm

I tried that many moons ago, and the house would never reach the t-stat setting. We froze! I tried just about every single point in it's range with similar results, eventually going the other way where the t-stat was never satisfied, and the burner ran non-stop.

Where they're set now gets the house just about right on the t-stat setting, unless it's below zero out.

 
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Post by franco b » Thu. May. 04, 2023 12:29 pm

SMITTY wrote:
Thu. May. 04, 2023 12:14 pm
I tried that many moons ago, and the house would never reach the t-stat setting. We froze! I tried just about every single point in it's range with similar results, eventually going the other way where the t-stat was never satisfied, and the burner ran non-stop.

Where they're set now gets the house just about right on the t-stat setting, unless it's below zero out.
I am not referring to the temperature setting of the thermostat, but to the setting of the tiny built in heater under the thermostat cover. Usually a sliding pointer and the word "longer" on it, if Honeywell. That little resistance heater supplies just a little heat when the thermostat calls for heat to prevent overshooting the temperature setting. If too much heat is supplied, the thermostat will short cycle. Set it all the way to longer.

 
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Post by SMITTY » Thu. May. 04, 2023 12:31 pm

That's what I was talking about - whenever I changed the position of the anticipator, it changed the temperature of the house, regardless of the t-stat temperature setting.

 
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Post by franco b » Thu. May. 04, 2023 12:42 pm

SMITTY wrote:
Thu. May. 04, 2023 12:31 pm
That's what I was talking about - whenever I changed the position of the anticipator, it changed the temperature of the house, regardless of the t-stat temperature setting.
Setting it to longer should tend to make the house temperature overshoot. I suspect the voltage supplied to the thermostat is wrong, that the zone valve is supplying the current rather than the Honeywell control transformer. Assuming a Honeywell mercury tube thermostat, with bi-metal coil.

 
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Post by SMITTY » Thu. May. 04, 2023 1:01 pm

Like I said, I set it everywhere throughout it's range with corresponding results.

I don't think the issue has anything to do with the t-stat. I've studied this thing for hours over the past 20 years. It's just the way it behaves with the 2 zones, if they happen to call, close, then the other calls immediately after. Happens frequently in the shoulder season. If there was something that would interrupt the burner from firing for a minute or so, I believe this issue would disappear.

I appreciate your help, Franco. Don't mean to sound like I'm shooting you down - I've pretty much tried everything to cure this over the years.


 
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Post by coaledsweat » Fri. May. 05, 2023 7:35 am

Sounds like the aquastat is goofy, have you checked it for proper operation? It should run from low set point to high and shut down. If there is a call for heat during a temperature drop below the differential setpoint it will fire during that call. Anything else is wonky. Also check the bulb, may need some goose grease to help transfer the heat? The thermostats themselves should have no bearing on what the boiler is doing I would think.

 
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Post by Retro_Origin » Fri. May. 05, 2023 9:48 am

SMITTY wrote:
Thu. May. 04, 2023 10:47 am

Yeah .. that's what it's supposed to do .. BUT, when there's a light heating load, the 2 zones might call within seconds of each other, and drop out just as fast. That makes the burner light for 5 seconds, shut off, then refire seconds later and shut off again. Sometimes up to 3x this cycle will repeat.

This has been beating the *censored* out of this burner. I'm shocked the motor still works! Would've got 50 years out of it if not for the short cycling, though. Not to mention the waste of expensive heating oil. Since I plug in my stoker to the same aquastat power supply, it does happen on coal, too.

I'm thinking some kind of adjustable time-delay device in series with burner motor power is the answer for this. What say you?
Are you saying your heat zones are satisfied in only a minute or two? I need to move into your house!

 
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Post by Rob R. » Fri. May. 05, 2023 10:06 am

Whenever the burner is fired due to a heat call there is the chance that the heat call will end right after the burner fires. If you have small zones and an oversized boiler, that makes it even worse.

There are controls that will vary the differential to help with this - like the Beckett product you mentioned. Beckett didn't discontinue the Heat Manger because it didn't work, instead they came out with an aquastat with that functionality already built in.
Since I plug in my stoker to the same aquastat power supply, it does happen on coal, too.
You are running your EFM stoker off an aquastat in the oil boiler? That is a bad idea for multiple reasons. To fix this the right way you need to rewire your controls.

What are you using for zone valves and how are they wired?

 
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Post by SMITTY » Fri. May. 05, 2023 10:49 am

Aquastat is working as designed, has heat transfer goo on the bulb. Boiler is definitely oversized for light loads, since the house bleeds so much heat in winter. Zones are only satisfied quick this time of year - never in winter. I can feel a breeze out of just about every wall in this house in winter.

Yeah, I'm just using the aquastat that was originally on the oil boiler for coal control. Worked fine all winter. I've got a 3rd circulator just to circulate water between the oil boiler and coal boiler that runs 24/7 during coal heating. Keeps both units the exact same temp, top to bottom.

Zone valves are wired the same as they were wired presumably in 1996, a few years before I lived here.

What is the model number of that new aquastat that prevents short-cycling?
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Post by franco b » Fri. May. 05, 2023 2:00 pm

If you take the covers off the thermostats, you can see at a glance if they are still calling when the burner stops. It will also obviate heat anticipation with the cover off.

 
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Post by Retro_Origin » Fri. May. 05, 2023 4:41 pm

Is it wrong to say that if your unit is oversized just run off the low limit? That way when the thermostat calls the aquastat won't know any difference between that and any other kind of heat draw?

 
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Post by Rob R. » Sat. May. 06, 2023 5:24 am

SMITTY wrote:
Fri. May. 05, 2023 10:49 am
What is the model number of that new aquastat that prevents short-cycling?
Here is a link to Beckett's "Aquasmart" Aquastat:

https://www.supplyhouse.com/Beckett-7610A0001U-Aq ... mKEALw_wcB
Retro_Origin wrote:
Fri. May. 05, 2023 4:41 pm
Is it wrong to say that if your unit is oversized just run off the low limit? That way when the thermostat calls the aquastat won't know any difference between that and any other kind of heat draw?
Not at all. I would do the following:

Remove the wires from zone valves to "TT" terminals on triple aquastat, and install a RIB (link below) to run the zone circulator whenever one of the zone valves opens. This will result in the oil boiler maintaining the low limit without any regard for what is calling for heat, or not. You could also install a zone valve control (link below), which would clean up the wiring a lot and make it easy for you to use thermostats that require constant power. Once this is done your zone valves and circulator can run independently of the boiler - even if your burner goes down and the boiler goes cold, the water will still circulate (and not freeze).

I would also install dedicated aquastats in the EFM. The problem with using an aquastat in the oil boiler to control the stoker is this: When that circulator stops working for whatever reason, the stoker will run nonstop until the relief valve opens on the EFM. It is like having a thermostat in one room and the radiators in another - what happens when someone closes the door? You should also have a dedicated high limit control on the EFM, this will protect you from a timer malfunction.

I know this stuff isn't cheap, but the good news is I probably have some of the stuff needed on the shelf, and there are good deals on ebay if you are patient.

https://www.supplyhouse.com/Functional-Devices-RI ... 0-Vac-Coil

https://www.supplyhouse.com/Taco-ZVC403-4-3-Zone- ... h-Priority

 
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Post by Dave 1234 » Sat. May. 06, 2023 6:57 am

We have a few boilers set up with a 4006 and a 4006E aquastats . The 4006 is simple and easy to move settings for temp swings of the seasons . We wire the 4006E in series , and use it for a safety , its set at 200, and is a manual reset . Just incase the stoker does a run-away .

The units are FS on ebay, at about 50 bucks each .

Boilers seam to like them , and its inexpensive.


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