Honeywell L8124A, C, L8151A Triple Aquastat

Am I missing something here? The only thing we are using is the burner control and I'm getting some odd behavior it seems.

Bulb is seated correctly as far as I can tell and I actually have two of these units and both are doing the same thing. One is the original and the other is off the oil boiler, same models. The hi limit seems to have no effect, previously if it was stoking and I turned the hi limit down to the temperature the boiler was at it it would shut off stoker, not the case here. Just a simple example of what just happened, the hi is at 160 and the low at 140. Diff is set at 10.

The boiler is stoking and the temperature is up to 180? How is that? Turning the hi to any amount does not shut off the stoker. Water started pumping out (keep in mind the tstat and circulate are independent) water temperature dropped to 160 and it stopped stoking?

The only thing I can think of is the temperature gauge is above where the aquastat is, could it take that long to equalize?

It sounds like stratification. The hottest water weighs the least, and will collect at the top of the boiler. The installation of a bypass pipe between the supply and return would help correct this.

I can turn the hi to any amount and it doesn't shut it off?

Disconnect the wires an meter it. See if the switch is opening and closing.
Maybe a wire grounding or in the wrong place.

Richard S. wrote:I can turn the hi to any amount and it doesn't shut it off?

I was referring to the difference you observed between the gauge at the top of the boiler and the behavior of the high limit you described earlier...when it shut off at 160 degrees. I must have breezed over the part about the high limit not having an effect at any temperature. That certainly isn't right. Make sure everything is wired properly (shouldn't be much, B1/B2 for the stoker).

Perhaps the aquastat is messed up, or if you have a timer wired directly to the stoker power....the timer could be sticking.

markviii wrote: Make sure everything is wired properly (shouldn't be much, B1/B2 for the stoker)..

Exactly that is the only thing wired to it, no timer yet either. Again it's two units with same behavior.

Now I just went out and it turned off at 160 which is hi limit, in this configuration since there is no circulation or t stat the hi really becomes irrelevant doesn't it? It shouldn't stoke past 150 if the lo is 140 and the diff is 10 right?

I'm just really baffled.

Richard S. wrote: Now I just went out and it turned off at 160 which is hi limit, in this configuration since there is no circulation or t stat the hi really becomes irrelevant doesn't it? It shouldn't stoke past 150 if the lo is 140 and the diff is 10 right?

I'm just really baffled.

If the Low is set at 140 with the differential set at 10, the temperature should fluctuate between 130 and 140 degrees. The high limit is basically acting like a second limit control; it shouldn't do anything unless the water temperature actually reaches that setting. Try this...turn the low limit up until the stoker starts, then turn the high limit down to the same setting...the stoker should shut off.

Going by the gauge makes it tough, they are often inaccurate and yours is mounted in a different spot in the boiler.

markviii wrote:Try this...turn the low limit up until the stoker starts, then turn the high limit down to the same setting...the stoker should shut off.

It doesn't... If it's stoking I can turn it all the way down and it continues to stoke.

I don't know if this is possible, but perhaps the high limit function on this model aquastat only functions if there is a heat call via the TT terminals? You could jump those two terminals with a piece of thermostat wire and experiment...

markviii wrote:I don't know if this is possible, but perhaps the high limit function on this model aquastat only functions if there is a heat call via the TT terminals?

Not according to the manual: https://customer.honeywell.com/techlit/pdf/packed ... 5-6571.pdf

Page 7 gives run down of the hi/lo/diff settings.

I had a similar occurrence a few months ago. My boiler was about 220 degree and still stoking away.
Never did find a cause for it. I even removed my timer from the circuit. It still was stoking.

Troubleshooting L8124a Aquatstat?

This might be the 3rd time I've heard of this.

Richard S. wrote:

markviii wrote:Try this...turn the low limit up until the stoker starts, then turn the high limit down to the same setting...the stoker should shut off.

It doesn't... If it's stoking I can turn it all the way down and it continues to stoke.

I just tried this experiment on the L8124C on my oil boiler. The high limit will shut off the burner regardless of if there is a heat call or not. It sure seems like something is messed up with your aquastat. If you want to replace it, a simple L4006A will hold the boiler at temperature just fine.

The thing is I have two of them doing it but then again I might be mistaken. The first one didn't have the bulb seated right and I really didn't have a chance to try it with it seated right.

As far as anew one goes do they have anything with a timer on it?

Richard S. wrote:As far as a new one goes do they have anything with a timer on it?

Not that I am aware of. If it were my boiler I would probably install a pair of L4006A aquastats and an Intermatic timer. One L4006A will maintain the boiler temperature, the other would act as a second high-limit cutoff. e.g. One would keep the boiler 150-160 degrees, the other could be set at 200...just in case the first aquastat gets messed up. You would connect the timer circuit between the two controls...that way if the timer malfunctions you still have a high-limit in play.

Of course there are many different ways to control the boiler....