American Standard Acroliner - varying hot water temp

is the boiler set up as hot water or steam? i'm thinking the boiler is low on water so the coil isn't fully submerged.

or the low setting on the aquastat isn't working right. or the heat call keeping the boiler at the heating temp was making more hot water

my bet is on the thermostatic mixing valve sticking.

the coil looks newer but that aquastat looks original

If you look at the controls just above the burner (sometimes inside an extended metal jacket with a metal front door), you should see three separate controls:

1. High limit control
2. Reverse (circulator) control
3. Circulator relay (also operates the burner on a call for heat) Sometimes on the wall near the boiler.

Another control is attached to the coil flange plate

1. Operator control is installed in the coil flange plast as you have pictured may not be inside the boiler jacket

High Limit Control

The high limit shuts off the burner if the boiler water temperature gets too high.
This is usually set at 180°F or 190°F.

If the boiler temperature reaches that setting, the burner shuts off regardless of other demands.

Reverse Control

The reverse control is so named because it makes on temperature rise and breaks on temperature fall — the reverse of a high limit.

It is commonly set around 140°F.

Its purpose is to give domestic hot water priority. If the boiler temperature drops below its setting, it shuts off the circulator pump to prevent sending heat to the radiators. This keeps enough heat in the boiler to maintain adequate hot water for the tankless coil.

Circulator Realy

The thermostat is usually connected to this control. The burner is also connected to this control and the circulator pump is connected to this control

On a call for heat the burner will operate as long as the water temperature in the boiler is belos the high limit setting

On a call for heat the circulator pump may operate as long as the boiler water temperature is not below the minimum reverse temperature control setting

Operating Control (Tankless Coil Control)

The operating control is usually installed in the tankless coil flange plate.

It operates the burner in a similar way to a thermostat, but it only controls the burner — it does not operate the circulator.

It typically maintains boiler temperature between 150°F and 160°F:

• Burner cuts in around 150°F
• Burner cuts out around 160°F

This keeps the boiler hot enough year-round to provide domestic hot water.

Why You May Be Getting Colder Hot Water

Possible causes include:

• The coil may de scaled
• The mixing vave may be failing
• The reverse control set too low
• The operating control set too low
• The high limit set too low
• A combination of these

Summer Operation (No Call for Heat)

• The boiler maintains approximately 150°–160°F continuously.
• The tankless coil sits in the hot boiler water.
• The domestic water in the coil reaches boiler temperature (which is scalding hot).
• When you open a hot water tap, very hot water leaves the coil and reaches the mixing valve.
• The mixing valve blends in cold water to deliver about 120°F to the fixtures.
• As water flows through the coil, it has less time to absorb heat and may leave at a slightly lower temperature.
• The mixing valve senses this and reduces the amount of cold water it adds.
• As boiler temperature drops, the operating control turns the burner on to restore the boiler to 160°F.
• The burner may cycle several times during long hot water use.

Winter Operation (Call for Heat)

• A thermostat calls for heat.
• The circulator runs and sends hot water to the radiators.
• Cooler return water from the radiators lowers the boiler temperature.
• If the boiler temperature drops to the reverse control setting (around 140°F), the reverse control shuts off the circulator to protect domestic hot water production.
• The burner continues running to raise the boiler temperature.
• When the boiler temperature rises again, the reverse control allows the circulator to restart.
• This cycling can repeat several times during a long call for heat.
• If the boiler temperature rises to the high limit (around 180°F), the burner shuts off, but the circulator continues to run until the thermostat is satisfied.

During the entire call for heat, someone can take a shower without losing hot water because the reverse control prevents the system from sending all available heat to the radiators.

Thermostatic valve according to Google. Any suggestions on unsticking it? My first thought is heat but given the solder, I dont know, and don't think that'll work for scale build up

This is the install and maintenance instructions for that valve: Watts 70A valve and this is the replacement temperature sensor: Watts 70A Repair Kit.

Any good way to test the aquastat? When I was talking to our oil guy, he said they made a line at black line and the current used mark. He said one was set for hot weather and one for cold?

That was a thing that some people did to lower their fuel usage in the summer. You should be fine at 160° if the control is still accurate after 70 years. It probably is.

The potable water side coil cleaning. Whats the process? Like flushing a heater core/radiator with cleaning solution in one and out the other, or unbolting those7 bolts and taking out the unit?

That will involve adding some valves to that coil so you can pump a cleaning chemical (mostly vinegar) thru the coil for about 30 minutes. That procedure is done with the coil in place on the boiler so you do not need to remove it.

Piping diagram to follow:

This is the piping arrangement you ahould be looking for. You should already have Valve B. You may need to add Valve A and C. Then you must add draw off valves (also called boileer drain valves) D and E and get an inexpensive utility pump. We used to use a really economical pump that you attach to an electric drill.

Close valve A B and C then attach hoses as shown to D and E and open those valves. Pump the cleaning chemical thru the coil for about 30 minutes. Then close E and open B to flush out the chemical. close D whan the water runs clear and open A and C. You should be good to go.

Agree with @hot_rod on upgrading to a ASME 1070 listed valve while repiping for the flushing valves

WOW… you still have an RA117A primary safety control? That is obsolete and has poor safety performance. You should think about removing that from the system completely if it is still connected. Replce it with a much safer primary safety control like the Carlin 70200 PRO. It is a much safer control for your oil heat system, and it should be installed by a professional.

The black covered box installed just below the vent connector (smoke pipe) is your circulator/burner relay. The thermostat wire connects tothat control and should turn on the circulator pump and also the oil burner by way of the RA117A primary safety control, Honeywell called the primary safety control a "Protectorelay®". I would strongly recommend upgrading that control. The Honeywell version of the Carlin 70200 is the model number R7184U protectorelay. But I would still recommend the Carlin control because it has the most safety and diagnostic features.