Oil boiler high/low temp

jmoser201

Recently moved into a home that has an oil boiler which provides hot water for baseboard heating and an indirect hot water tank. I just had a plumber/hvac guy out to replace the expansion tank and he noticed the Honeywell high/low setting which is currently set at 180/160 with a diff of 10. He said the low was set too high and put it at 120. I researched and that seems way too low for an oil boiler, but I’m not an expert. Does anyone know what the best settings would be for my system? It’s a peerless boiler from 1989

STEVEusaPA

The first thing to determine is if the knobs are measuring the boiler temperature accuratly.
Do you have a tankless coil (coil inside boiler to make domestic hot water) or an actual indirect storage tank?
You must have a mixing valve to temper the water reaching the fixtures, in either scenario.

If you have an indirect, I would change the aquastat to something like a Hydrostat 3250 plus. Make it cold start, low limit off, and utilize circulator hold off, as well as the other features.

If you have a tankless coil, the temperature of the incoming cold water directly affects the domestic hot water output. Right now 120/160 might be fine, but when your incoming cold water gets down into the high 30's/low 40's, you won't get the hot water you need for showers.
If it is a tankless coil, you need to realize you are making domestic hot water in the least efficient, least consistently comfortable manner, with ancient technology.

jmoser201

STEVEusaPA said:

The first thing to determine is if the knobs are measuring the boiler temperature accuratly. Do you have a tankless coil (coil inside boiler to make domestic hot water) or an actual indirect storage tank? You must have a mixing valve to temper the water reaching the fixtures, in either scenario. If you have an indirect, I would change the aquastat to something like a Hydrostat 3250 plus. Make it cold start, low limit off, and utilize circulator hold off, as well as the other features. If you have a tankless coil, the temperature of the incoming cold water directly affects the domestic hot water output. Right now 120/160 might be fine, but when your incoming cold water gets down into the high 30's/low 40's, you won't get the hot water you need for showers. If it is a tankless coil, you need to realize you are making domestic hot water in the least efficient, least consistently comfortable manner, with ancient technology.

We do have a 35 gallon storage tank, so the boiler is creating the hot water and storing it in the tank. I’m assuming we have a mixing valve, because the water comes out of the faucets at a normal temp of 120 or below

jmoser201

Here are pictures of the full setup 

HVACNUT

As long as the valve feeding the tankless coil is off, do as @STEVEusaPA mentioned and look into the Hydrostat 3250 Plus. 
 
A safer primary control couldn't hurt either. 

Also the 3 section JOT was always a tight boiler and the evidence is on the jacket around the front plate. A thorough cleaning and replacing the kaowool rope gasket around the front plate would be good.

STEVEusaPA

I'm having a little difficulty understanding your picture, maybe move to the right a little. It doesn't appear to be piped correctly. Looks to me the water can flow thru the coil and completely bypass the tank.
Usually with your arrangement, cold water flows thru the coil, and the outlet of the coil goes to the inlet of the tank, and the outlet of the tank goes to the fixtures.
Also I don't see a mixing valve.

Robert O'Brien

STEVEusaPA said:

I'm having a little difficulty understanding your picture, maybe move to the right a little. It doesn't appear to be piped correctly. Looks to me the water can flow thru the coil and completely bypass the tank.
Usually with your arrangement, cold water flows thru the coil, and the outlet of the coil goes to the inlet of the tank, and the outlet of the tank goes to the fixtures.
Also I don't see a mixing valve.

Agreed, it looks teed in, although the path of least resistance is through the tank, eliminate the coil completely. Cold start the boiler, the indirect will call often enough to prevent condensation.

jmoser201

Robert O'Brien said:

I'm having a little difficulty understanding your picture, maybe move to the right a little. It doesn't appear to be piped correctly. Looks to me the water can flow thru the coil and completely bypass the tank. Usually with your arrangement, cold water flows thru the coil, and the outlet of the coil goes to the inlet of the tank, and the outlet of the tank goes to the fixtures. Also I don't see a mixing valve.

Agreed, it looks teed in, although the path of least resistance is through the tank, eliminate the coil completely. Cold start the boiler, the indirect will call often enough to prevent condensation.

Ok, so you’re saying I should be fine to leave the low set to 120?

HVACNUT

With the valve off on the cold at the tankless, only the indirect will see the draw.
I guess if the indirect fails (relay or circulator), the hot and cold can be closed at the indirect, open the cold at the tankless and use it temporarily. 
It can't be wired cold start though in that case.