Aquastat Question


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Old 01-03-06, 11:48 AM
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Aquastat Question

The aquastat on my gas fired hydronic boiler is a Honeywell L8052A 1037. I understand it has been replaced by a L8148A 1017, but alas, I am still using the old model. Like others I have a cycling problem. Water heats to about 152, gas shut off, temperature falls to 150, then it fires up again. It cycles like this on about a two minute cycle until the thermostat is satisified.

I expected to see two adjustable set points in the aquastat so the range could be lengthen. Other than the emergency high temperature shut off (set at 220) there is none. However, there is a small plastic wheel which is graduated from 0 to 30 in increments of 5. The boiler was set on 30, so I turned it down to 15 with no affect.

I guess I probably should replace the aquastat as I assume the cycling is putting undue stress on the automatic gas valve. My question is, what is this small plastic wheel controlling?

Thanks in advance for any help.
 
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Old 01-03-06, 05:11 PM
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Aquastat

I'm not familiar with the L8052 but on the L8148 there is a metal wheel which is marked at various temperatures. Above this wheel there is a pointer. One would line up the pointer with the temperature desired. The 8148 does have a stop at 220 as well.
The small plastic wheel is a differential setting. It's purpose is to adjust the temperature between burners off & burners back on. For example: If the metal wheel were set to shut the burners off at 180 & the differential were set at 20, the burners should re-fire at (or about) 160, provided the thermostat was still calling for heat.

I moved this post because it pertains to hot water heat.
 

Last edited by Grady; 01-03-06 at 05:14 PM. Reason: Explanation for moving
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Old 01-04-06, 08:23 AM
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Thanks Grady. That makes perfect sense, and sorry for posting on wrong forum.

The metal wheel in my aquastat has only one pointer (actually looks more like a clamping mechanism that would take a screwdriver to move it). Therefore, I am assuming it is the high temperature cup off and is made to be somewhat tamper resistant. I will check behind this wheel to see if maybe a pointer has been broken off. But still changing the small plastic wheel doesn't increase or decrease the temperature range.

I just purchased the house and the boiler is 40 years old, but seems to work okay. I assume the aquastat is 40 years old also. My best bet may be to put in a new aquastat.

Thanks again.
 
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Old 01-04-06, 05:08 PM
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Twich

I tend to agree on the idea of a new aquastat. In the meantime, try turning the metal wheel somewhat & run the boiler thru a cycle to see what happens.
 
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Old 01-07-06, 02:18 AM
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If memory serves me correctly an aquastat does not have a temp. differential setting. Normaly they are used to prevent a fan from running on a unit heater, of one type or another, until the water temp. reaches a certain setting. This is done to prevent blowing cold air. What you should have is an operating limit control. I think I'm right
 
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Old 01-07-06, 05:02 AM
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I would tend to agree with melligene because I have been servicing hot water systems for over 20 years and can't remember ever seeing that model control. It may have been for a specific purpose and was not widely used in the residential market. I also agree that you would be better off if you installed a current model of the proper control for your system.

Ken
 
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Old 01-07-06, 09:33 PM
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Originally Posted by melligene
If memory serves me correctly an aquastat does not have a temp. differential setting. Normaly they are used to prevent a fan from running on a unit heater, of one type or another, until the water temp. reaches a certain setting. This is done to prevent blowing cold air. What you should have is an operating limit control. I think I'm right

Not true.
An aquastat is simply a device that uses the temperature of a fluid in relation to a setpoint to open or close an electrical contact.

There are many different models that all fall under this category. There are the simple single function aquastats that are usually used on hydro coils - such as the L4006A 1009 which has an adjustable high limit of 100F to 240F and a fixed differential of 5F. There is also the L4006A 1017 which has the same high limit, but an adjustable differential of 5F to 30F.

Then there are the multi-function aquastats that combine different functions. Such as the L8148A 1265 which uses a room thermostat to control the system circulator and the burner. This is a cold-start aquastat that doesn't run at all until the thermostat calls for heat. This unit has an adjustable high limit with a fixed differential of 15F.

Then there are the multi-function triple aquastats. Like the L8124A 1007. This unit has high limit, low limit, and circulation control with fixed 10F high limit differential, and a 10-25 F adj. low limit differential. These controllers keep the internal boiler temperature between the high limit and low limit settings (minus differential) all the time. These are used on boilers that have a tankless coil in them.


twitch,
I couldn't find any information about the L8052A 1037 on Honeywell's website, so I don't know anything about it. If it's similar to other aquastats, look straight down at the metal dial. There should be a small pointer on the dial housing just above the dial. Whatever number that's pointing to is what the water temp is trying to acheive. The "clamping mechanism" is to prevent the dial from being turned too far. This does not affect the operating temp of the boiler.
If as you're saying that changing the differentail knob does nothing about the short cycling, something's broken. I would just replace it with a newer model.

Do you have a tankless coil in your boiler? If you do, you'll need a triple aquastat such as the L8124 or digital L7224.
If you don't have a tankless coil, or have an indirect, then you can use the L8148 or digital L7224(set up for cold start).

Michael
 
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Old 01-10-06, 01:20 PM
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Thanks to all - Michael, according to Honeywell the L8052A 1037 (40 years old) is replaced with L8148A 1017. I too now believe something is broken, and will replace the control.

Thanks again.
 
 

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