L8124 Aquastat settings...does this look right?

MichaelG

I recently moved into a house with an oil fired hot water boiler heating four zones, each with an independent circulator. The boiler is controlled by a Honeywell L8124C aquastat, which also handles circulator control for one of the zones. Three other zone control relays (R845A) handle the other zones.

I'm afflicted with being an engineer and so I can't help staring at things for a while, which I have done with this boiler. I noticed something which has me puzzled. If you're an expert with this aquastat, perhaps you'll be able to follow along as I describe its operation.

I walked up to it tonight and the thermostat on the boiler read about 200F. This is perplexing to me because the aquastat settings are LO: 145F HI: 160F DIFF: 20. By my study the thing should run from 135 (10 below LOW) and 160 (HI). To try to understand a little better, I shorted the TT to maintain a constant call for heat, and the following took place (the other zones' tstats were all off).
1) the circulator turns on
2) after a long period of time, the boiler's thermostat eventually drops to 160
3) the boiler fires up and the circulator turns off (call for heat still active)
4) the boiler shuts down when the boiler thermostat reads about 190 (call for heat still active, circulator still not enabled)
5) moments after the boiler shuts down I hear a quiet click from inside the aquastat and the circulator starts to run again (its relay coil had been active this whole time)
6) a few minutes later the boiler thermostat has risen above 200F (heat soak I presume)

Things I'm confused by:
1) Why does the boiler appear to be getting so hot? Is it possible the thermostat is just wrong? Is it more likely the temp probe on the aquastat has some kind of an issue?
2) Why does the boiler not turn on earlier when there is a call for heat active? It seems to wait until presumably the low point has been hit (thus disabling the circulator) rather than running to stay at a temperature that would permit the circulator to keep running

The way it's set up now, it seems to let a circulator run until the boiler fires, at which point the circulator is disabled until the boiler builds up another 30F and shuts off.

Is this fine? If not, what should I tackle first? I see that the LO and HI should be separated by at least 20F according to the documentation, and they seem not to be.

For reference, a photo of the aquastat settings and boiler thermostat in the background:

Paul48

Is there a wire on C1 in the aquastat?

Alan Welch

Looks like you also get your hot water from the boiler , cooler water flowing through the coil will affect/effect the aquastat. Also if the 3 relays are wired properly using the zc and zr terminals from the aquastat , a call for heat from any of the zones should start the burner provided it's not off on hi limit. Are all the terminals on the 845 relays being used?

newagedawn

the diff souldnt be more than 15

Ron Jr._3

2 things I've noticed on boilers. The tridicator gauge can be way off sometimes. Can you verify the temp by another means ?

And the boiler temp can override. I've seen it override by as much as 30 degrees in a Weil McLain.

Paul48

I don't see a wire on C1. If there isn't, what's controlling the circ for the zone that is suppose to be controlled by the boiler?

MichaelG

Paul48 said:

I don't see a wire on C1. If there isn't, what's controlling the circ for the zone that is suppose to be controlled by the boiler?

There is a wire on C1, it's slightly hard to see in the picture.

MichaelG

Ron Jr. said:

2 things I've noticed on boilers. The tridicator gauge can be way off sometimes. Can you verify the temp by another means ?



And the boiler temp can override. I've seen it override by as much as 30 degrees in a Weil McLain.

What would be a good "other means"? I have a multimeter with a thermocouple attachment I could set against the pipe coming out of the boiler.

MichaelG

Alan Welch said:

Looks like you also get your hot water from the boiler , cooler water flowing through the coil will affect/effect the aquastat. Also if the 3 relays are wired properly using the zc and zr terminals from the aquastat , a call for heat from any of the zones should start the burner provided it's not off on hi limit. Are all the terminals on the 845 relays being used?

The relays are wired properly.

The symptom I seem to be experiencing is that the aquastat goes into circulator lockout state (breaks R-W) without the boiler turning on. This seems wrong, since the boiler should turn on with any call for heat, unless the HI limit has been reached. Which makes me think that it has.

So I can make changes to these settings, but I want to be cautious so as to not raise the HI too high, or the LO/DIFF too low, since this boiler also handles tankless DHW.

My gut tells me that the combination of HI/LO/DIFF settings is not correct, or there is a component failure of some sort.

Paul48

I'd double-check the R845A's to make sure a "hot" and "neutral" haven't been flip-flopped. You have bizarre behavior going on. I'd disconnect everything to the other zones. Set the Hi to 170, Lo to 150, Diff to 10......run the boiler and see how it responds.

rick in Alaska

Look at the boiler gauge and slowly turn the dial on the aquastat and see that when it clicks, it corresponds to the boiler gauge. This is assuming the gauge is accurate. Do this with the high control and the low control.
I have had more that one of these controls where the aquastat was just reading way off, by as much as 40 degrees. That can mess with the circulator control if the high and low are overlapping.
Might be time for a new control if that is the case.
Rick

HomerJSmith

Yes, tridicators on older boilers can be off. Put your thermocouple as close to the outlet of the boiler as you can and insulate it with pipe insulation and read the temperature on your multimeter to confirm the accuracy of your tridicator.

If your aquastat is set at a lower temperature and the boiler is operating at a higher temperature, your aquastat is probably faulty. There can be a little overshoot of the temperature when the aquastat shuts the burners off, but it shouldn't be much.

If you replace your aquastat, be sure and clean your well with a wire brush and blow it out. Use heat transfer compound on the bulb when slipping it into the well.

unclejohn

My guess is you have a bad aqua stat. It set to maintian the boiler temp due to the domestic running through the boiler. Also from the looks of it that coil is not doing much. I would get a indirect or a electric water heater and get rid of the water coil in the boiler and then get a new control with just a high limit.

MichaelG

unclejohn said:

My guess is you have a bad aqua stat. It set to maintian the boiler temp due to the domestic running through the boiler. Also from the looks of it that coil is not doing much. I would get a indirect or a electric water heater and get rid of the water coil in the boiler and then get a new control with just a high limit.

This has been my thinking for a while now. Especially because the previous homeowner added a conventional heat pump to half the house and a 3 coil minisplit to the other half, almost all the time the boiler runs it's for the following reasons:
1- DHW (wasteful)
2- to keep the heating pipes from freezing and bursting (this happened once)

Between the standby losses and the confusing controls, I have to say I find this zoned baseboard setup to be pretty annoying.

I expect I will make the following changes:
1- Switch to an electric hot water heater
2- Replace the aquastat with a newer unit, maybe L7224?
3- Replace the mess of relays with a Taco SR504-4

HomerJSmith

It looks like you have hard water. I bet that the heat exchanger and hot water coil are calicified and a boiler cleaning is in order.

I bet your stack temperature are high, over 600 deg.

MichaelG

HomerJSmith said:

I bet your stack temperature are high, over 600 deg.

What makes you think that?

Incidentally I have decided to switch to an electric water heater. I just moved into this house and i can't believe people heated the boiler all summer long using oil just to take a shower!

HomerJSmith

Mineral deposits on the inside of the heat exchanger can radically affect the transfer of heat energy to the water. It doesn't take much of a deposit to interfere with heat energy migration. With mineral deposits, the heat energy goes up the stack rather than into the water, raising the stack temperature.