American Standard GPM Boiler Controls and Tune Up

mx6er2587 · February 3

Looking for some advice on the wiring and control setup for an old cast iron natural gas American standard boiler.

The boiler dates back to the 1960s I believe and has definitely had some modifications in its life. I believe the current setup is not optimal and would like to make improvements if possible.

I've been in the home a couple years and the boiler has been functioning "okay" until it recently wouldn't fire. I was able to diagnose the failure as a bad S8610 intermittent pilot controller. The controller (added in maybe the 90s?) Was not generating spark. In the process of replacing it I took a closer look at the whole system and am not thrilled. Note it did fire after replacing the controller.

First the wiring for the S8610 seems to be slightly off. The white thermostat wire is wired directly to 24 GND and the red wire from the 24vac transformer goes through a high temp limit switch before going to TH-W. I believe that the white thermostat wire should be hooked up to the high limit switch and then TH-W on the S8610. (I've attached wiring diagrams) Does this look correct?

Second the circ pump is not tied into the thermostat at all. In fact, it appears to only be controlled by a strapped on low limit aquastat. The aquastat is set to 135F so I assume the pump turns on when the pipe reaches 135F and just runs until the boiler is cool. This seems....less than ideal.

The original schematic indicates there should be a transformer/relay combination instead of just the remote 24v transformer currently installed and that this relay should be triggering the circ pump based on a call for heat from the thermostat. This would make more sense to me as the pump would then shut off once the call for heat ends. I would like to replace the transformer to add back this relay. Does this plan make sense? Should the aquastat be in the circuit at all?

Jamie Hall · February 3

I prefer the way it's wired now. Limit switch in series with thermostat. As to the aquastat, no reason for it not to be where it is. If you have hot water, it pumps as it should. If it doesn't it doesn't, as it should.

mx6er2587 · February 3

So the limit switch is currently not in series with the thermostat. It's wired to the transformer and the thermostat input on the s8610u.

My plan was to wire it in series. So it will stay connected to the TH-W on the S8610 but the other end of the switch will connect to the W thermostat wire instead of the transformer

hot_rod · February 4

Typically everything in the control string, aquastat, safeties, limit switch, thermostat and gas valve is on the 24 V side of the transformer. The schematic plate shows that.
Thermostat usually calls on the boiler, and a relay in the aquastat controls power to the circulator.
Burner and circulator stop when the thermostat is satisfied.

mx6er2587 · February 5

hot_rod said:
Typically everything in the control string, aquastat, safeties, limit switch, thermostat and gas valve is on the 24 V side of the transformer. The schematic plate shows that.
Thermostat usually calls on the boiler, and a relay in the aquastat controls power to the circulator.
Burner and circulator stop when the thermostat is satisfied.

So am I on the right track by getting something like an R8239A to replace the current transformer and using the relay to trigger the circ pump?

https://customer.resideo.com/en-US/Pages/Product.aspx?cat=HonECC%20Catalog&pid=R8239A1052/U&category=R8239&catpath=1.2.8.3.1&rank=1&v1=Sort.1.Product.Rank&asc=1

EdTheHeaterMan · February 5

There is some benefit to the circulator operation as it is. Think about this.

The limit might be set at 170°
On a call for heat in the coldest part of the winter the call for heat may last for over 20 minutes on any given hour.
The boiler temperature gets to the high limit setting and shuts off the burner.
Just then the call for heat is satisfied.
You end up with 170° (or more due to over run because the circulator pump stops)
Your chimney is working very efficiently since the chimney is hotter than the air around it so the draft is at the greatest.
That chimney is sucking all of the air thru the boiler room and the boiler itself
The only way the boiler can cool down is by venting the heat outside by way of the chimney
After you have all that wasted heat leave the boiler, to the outdoors you get another call for heat in 20 minutes or so.
Now you need to make up all that heat again from a cold boiler

There is a company called Energy Kinetics that uses that otherwise wasted heat to reduce the amount of energy used in a home by "purging" that wasted heat into the last zone calling for heat even if it is the water heater zone. .

One benefit to the minimum 135° starting temperature for the circulator may be that there is less chance of "Condensation of Flue Gas" in your boiler that can cause premature failure (no chance of that now since the boiler is over 50 years old LOL). But that may be one of the reasons the boiler is still in good shape. No doubt your boiler is oversized for the amount of radiators connected and the actual heat loss of your home. If you start the circulator and burner at the same time, you may find that the boiler temperature may not get to 135° in the mild seasons. The call for heat may be satisfied with 130° radiators in the spring and fall. This means that the flue gas never gets hot enough to burn off any condensation that forms on the boiler metal surfaces. The moisture will cause the cast iron the rust away.

By waiting for the boiler temperature reach 135° before introducing the cold return water from the radiators, the condensation will have burned off and evaporate into the chimney and be gone before it has a chance to cause any noticeable damage to the chimney, or boiler

If you boiler is not oversized, and you have copper with aluminum fin baseboard (that quickly returns warmer return water to the boiler) the nursing the relay may be a good idea, but I would still use the reverse aquastat to “Purge” the heat from the boiler on the off cycle. You just don't want to waste that heat. This diagram is what I might recommend for lowering the gass bill. You may save as additional 3% to 8% operating this way. OR eliminating the "Purge" you have may add 3% to 8% to your gas bill.

Think About It.

retiredguy · February 5

As @Jamie Hall wrote, "I prefer the way it's wired now". This is the way almost all cast iron boilers and heating systems using cast Iron rads were set to run when your boiler was installed. It is no time to try and re-invent the wheel. There is nothing to gain by adding a relay to cycle the pump with the thermostat. You could lower the setting on that strap-on aquastat to between 110F and 120F to utilize a little more of the boiler heat when the gas valve shuts off. By the way, that boiler is a good unit that should last 2 lifetimes unless it is abused. If it was installed in the 1950's it is now just coming of age.

ThatGuyOG · October 24

any chance you scrapped this idea and got a new boiler? I am looking for a cast burner. Id buy each if yours.

Ironman · October 24

Using the strap on aquastat to control the circulator is the best approach. It prevents thermal shock to the boiler and flue gas condensation.

That Nest is the worst possible choice for a hydronic system. Get a stat that’s designed for radiant heat and set it to 1 CPH.

mx6er2587 · November 18

https://forum.heatinghelp.com/discussion/comment/1815904#Comment_1815904

modified my plans based on the feedback here, but still running this boiler at least for this heating season.

American Standard GPM Boiler Controls and Tune Up

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