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:

STEVEusaPA

If you think the dials on that aquastat are the exact temperatures that things will happen, you'll be mistaken. You should probably switch it out to an electronic aquastat, with a new immersion well, and take advantage of the newer features like lwco, thermal purge, and circulator hold off.
On your gauge, the temperature is more likely to be correct over the pressure gauge.
For basic operation, when there is a call for heat from t-t or ZR, a circulator turns on if the temperature sensed by the control is above the low limit. The boiler only fires if the temperature sensed is below the high limit.
On a cal for heat, if your temperature sensed is above the high limit, the circulator will run until you are 10 degrees below high limit (fixed differential). The adjustable differential is for the low limit.

leonz

I have an L8124L1011 triple aquastat(horizontal) for my dual fuel coal stoker and I have had no problems with it.

Do you have a Mercury bulb thermostat(s) that is controlling the boiler operation?

As Steve said the temperatures will differ(higher) than the settings on the triple aquastat.

If your still concerned I would do this first before anything else.

Purchase a new 4 inch triple gauge from Marsh Instruments they have retailers nation wide.
The Marsh instrument triple gauge either the 4 inch round or square gauge is tested and certified and guaranteed for two years. these gauges have a bottom or rear 3/4" male pipe thread.

You also need to purchase a Mcdonnel and Miller RB-122-E Low water cut off it is a direct conductivity low water cut off without an immersion well if your system does not have a low water cut off protection.
You can buy this low water cut off from any plumbing supply store that handles B+G products

Wire the low water cut off as the very first control mechanism before your triple aquastat and your boiler will be protected in the event of a low water/water loss condition and it will shut the boiler down completely-this is the recommended way to protect a hydronic boiler and they can be installed four ways in your system;
1. horizontal in the header pipe
2. vertical in the header pipe
3. horizontal in boiler side tapping
4. horizontal in riser pipe.

I had 2 bad Hydrolevel triple aquastats go bad -the first one almost blew up my house and the second one turned off the low water cut off function which I programmed into the aquastat while I was watching it run on oil.



Buy a Marshalltown triple gauge and a McDonnel and Miller Guard Dog RB-122-E low water cut off first and you will be better able to watch your boiler if you are worried about its functioning properly.