Aquastats

jjccl

I think I'm losing it. I've been living here 45 years with the same hot water heat oil fired furnace. Every summer I set the aquastat down to 110 to save a bit of money and prevent the furnace from going to ambient and (in my mind risking the sections from leaking) Anyway, earlier this winter I was in the basement doing some cleanup since we had a few warm days back to back.

I noticed the furnace water temp was all the way down, I cant remember ever seeing that so I thought the aquastat was defective. I took the part# and learned there were different design aquastats. High temp only, high and low that would fire the furnace based on a low setting. Evidently mine was high only, but I never saw the water temperature all the way down before, strange.

My question is are there other possible relays that do this that could have failed? Once I turned the thermostat up the furnace came to temp

delta T

Is there a differential setting on the aquastat? Usually a white wheel with numbers on it.

STEVEusaPA

Show us a picture of it, or the make and model number, usually on the cover.
In all likelihood it's an older model that just isn't that accurate anymore, for a number of reasons.
If yours is high limit only, the burner should only run when the thermostat calls for heat. And you should leave it at 170°. If you have a high limit and it's wired to maintain temperature, and it's just for heat, well that's just wasting fuel. Turning down the aquastat will cause short cycling and allow your boiler to condense, which isn't good for the health of your boiler.
How are you 'keeping the boiler warm' when it's not needed for heating?
If you have to keep your 45+ year old boiler warm when it's not needed, just to keep if from leaking, you need a new boiler. The improved efficiency, lower water content, proper controls, properly sized, and not running it when you need it, alone will go a long way in making up what you are wasting trying to keep it warm.
Especially when you look at something like an Energy Kinetics, with an overall system efficiency in the low 90's vs. what you have, something with a system efficiency in the 40-50's. Savings would add up pretty quick, depending on how much oil you use in a year.

jjccl

jjccl

Robert O'Brien

Both the 4006 and 6006 are lot more than 45 years old. Looks like cloth wiring?

jjccl

45 yrs is how long I've owned the house and never seen the water temp at ambient, my father built the house in 1950

Robert O'Brien

STEVEusaPA

What's in the other gray box? That's you're operation control.

jjccl

😬 dunno, gotta look....

EBEBRATT-Ed

Looks like the wire are on R & B terminals (although hard to tell) (Red to Blue for BTU) which would make this a high limit control.

I would set this at 190 if that is the case

EBEBRATT-Ed

It cold be an old "non intigrated control system" Very common on old boilers. Low limit runs the burner to maintain temp. The circulator starts when the thermostat pulls in the relay next to the aqaustat. Tstat does not control the burner.

Very common on old jobs.

But then the boiler would have to have two aquastats 1 high limit 1 low limit

HVACNUT

The cover says L6006A but it's an L4006A. Break on temperature rise. It must be a fixed differential on the early model because the dial isn't there. 
Does the boiler have a tankless coil? If so there should be another aquastat. Maybe the covers were switched. 

EdTheHeaterMan

You cant be sure of anything with a 70+ year old boiler. That oil burner is not a 1950 design. So the burner may have been replaced/upgraded in the 1970s (or later). O'Brians diagram may be the wiring design for that 1950 boiler but the tankless coil (if there ever was one) has long been abandoned and the boiler may not need to maintain 110° all summer.

If it did then there is another L6006 aquastat control where the tankless coil would have been located. If the boiler never has a tankless coil the wiring diagram would look more like this one.


So look for another control that looks like the L4006 you show in the photos

Yours Truly,
Mr.Ed

PS
I wonder if you still have a stack relay? In 1950 they were very few "Cad Cell" relays In the 1970s they were becoming more popular.