Aquastat Relay Difficulty

ccstelmo

Woulda-Coulda-Shouda thought of asking you guys about this earlier. But I get into autopilot, and that, combined with my natural independent streak, led me into a black hole and now I need help getting out.

Honeywell L8148A aquastat . I mounted it on the supply of my 250K btu LP Fired Buderus boiler just upstream from the pump 20 years ago (and ran the end switches from my Taco Gold (571) zone valves over to it and called it good.

Time (about 5 years) went by, and the high limit went south. I replaced it. This has happened regularly ever since. The not-dead-guy behind the counter would roll his eyes and agree with me that that particular aquastat always gives guys the fits and someday somebody oughta do something about it. But that day hasn't come yet and here I am again.

The high limit fails, the boiler overheats all the way to 250 degrees, fluid flashes to steam and the boiler dances around and makes a racket and my wife wigs out. Of course, it's a Friday or, in this case, Thanksgiving Day and the people are coming for Turkey and Pecan Pie and such and, deservedly or not, I have a local reputation of being the Heating Yoda of the town because I've successfully pulled the wool over their eyes all these years and now the cat's going to be out of the bag and it'll be humiliating and embarrassing and 'm not up for it. But alas, there's no getting out of it.

Now, I know you guys aren't dead yet (but you should be so you could get some respect, and someone would listen to you) but, with me at least, you have more credibility than the guy behind the counter. And I'm desperate so I have to humble myself and ask for help.

OKAY — That's my mea culpa

So what do you think? My conclusion is that that the L8148 series is and always has been a faulty design. Why, in the hey-day of its popularity, that never came up and never got fixed is a mystery. But the fact now is, it'll never get fixed because technology has made it obsolete anyway. Sheesh, even Honeywell has abandoned it and spun it off to brand X. What do I do? Is there now an alternative? (The burner contacts on the L8148A are line voltage and I have a Riello power burner as a concession to the reality of getting a decent flame at 10,000 feet elevation)

Desperate in St. Elmo Colorado, ccstelmo

jesmed1

I'm not an expert, but we have two 30-year-old boilers, both with what appear to be original L8148A aquastats that have never given me trouble in the 15 years I've lived here.

I wonder if the quality control problems are a more recent phenomenon. That seems to be common with many things these days, that the new stuff isn't as good as the old stuff, even with the same part #. The bean counters try to save pennies by "value engineering" the quality right out of the part.

Jamie Hall

The Honeywell/Resideo L8148 series controls are about as simple — and reliable — as it gets. What you are experiencing is one of three problems: either the burner contacts of the high limit fusing from opening on excessive current or damage to the capillary causing the capillary to not activate the burner contacts or shifting of the sensing bulb in the well so it doesn't monitor the boiler temperature.

My bet is going to be fusing of the high limit contacts from opening on overcurrent, though why that would be happening if the only thing it is controlling is the burner I'd not care to say.

LRCCBJ

EBEBRATT-Ed

I would find out why it is constantly hitting high limit during normal operation.

The high limit is ment to be exactly that……a high limit it is not supposed to work as an operating control under normal use.

Perhaps the boiler is oversized or being fired too hard.

Perhaps the HL is set too low

Find out why the boiler is delivering more heat that the radiation can disperse.

LRCCBJ

Ed.

The high limit is the operating control on the L8148.

The boiler always delivers more energy than the radiation can dissipate under steady state conditions (unless by some act of God the installer put in a boiler that matched the radiation!) Even in that condition, there can be only one zone for the boiler to fail to meet HL.

LRCCBJ

Another L8148 failure……………

https://forum.heatinghelp.com/discussion/198886/honeywell-aquastat-l8148e1166

Not quite as reliable as some believe.

109A_5

Hello ccstelmo,

It seems the typical failure of those aquastats usually leaves you getting cold, not " The high limit fails, the boiler overheats ".

I'd figure out what part of the L8148A is actually failing, then possibly you can make that part of the system more robust.

Burner relay contacts welded together,

Capillary tube, bulb, diaphragm failure,

The microswitch that the diaphragm pushes against for the heat sensing fails to open (shut off).

BTW if the relay contacts are getting welded together the '120 Vac Oil Electronic Aquastat, L7224U1002' may not be any better since the relay contact ratings seem the same as the L8148A.

HomerJSmith

The sensor bulb may not be reading the boiler water temp accurately. The boiler sensor well should be wire brushed out and heat transfer compound used on the bulb. I do this with any aquastat replacements.

ccstelmo

Thanks, guys. You've gotten me closer. I'm not tinkering with this thing. I'll replace it as I always have. For the last 24 hours the high limit has been behaving itself but the control will not keep the boiler temperature up regardless of where I set the high limit. Right now the delta T on the boiler is close to 65 degrees and I am indeed getting chalk in the flue. (Haven't looked inside the combustion chamber. Afraid to.) I did fail to mention that in order to save on fuel we close off rooms and turn down thermostats in this 5040sf house/ B&B and live in about 25% of it during the off season. The heating load is way down and the boiler is sized at 205K btu input and derated 2%/1000 feet.

If a guy is patient he can wait for the supply temperature to fall from 175 to 130 before the burner kicks on. At that point the boiler return is 110 degrees. Pretty grim scenario.

L8148A spec sheet sidesteps the fixed differential information. Somewhere I read it was 8 degrees but I haven't been able to remember where. That would be interesting to know if anyone can tell me.

Regarding the capillary and well. OK, that sounds like a possibility. I confess I've just slathered on more silver stuff and jammed the tube in there each time I've swapped the control out. I'll be more diligent this time.

I'm back out on the road for a few days and won't be getting the part in for a while anyway but I'll let you know what happens

ccstelmo

EdTheHeaterMan

Check the EDIT at the bottom

@ccstelmo Said: "Honeywell L8148A aquastat . I mounted it on the supply of my 250K btu LP Fired Buderus boiler just upstream from the pump 20 years ago… …and called it good."

Why didn't you install it in the Buderus boiler's recommended aquastat location?

From your description, it sounds like your aquastat is at Location A. When it should be at Location 3. Don't exactly know what Buderus Boiler you have, but if you look in the manual you will find the recommended sensor location.

As far as the Honeywell L8148 controls are concerned, I used lots of the L8148A on oil heat boilers of all makes and models. I have also used the L8148E on gas boilers to a lesser amount. I don't seem to find that failure rate you are experiencing.  Before I retired, I started to use the Electronic controls because they were less expensive and you could purchase one model and use it for several different analog controls, so there were less parts to stock on the service trucks.

Anyone that recommended that you try the L7224U control didn't pay attention to the fact that you have a LP Gas boiler. That control does not have the 6 pin Molex plug for the automatic vent damper, and the B1 - B2 circuit is 120 VAC. You need a B1 - B2 circuit that is 24 volts for the gs valve circuit. the proper electronic control is the Hydrolevel 48-3200 https://www.supplyhouse.com/Hydrolevel-48-3200-Model-3200-Plus-Fuel-Smart-Hydrostat-for-Gas-Boilers-Temperature-Limit-LWCO-Boiler-Reset-Control That control is for a 24 VAC gas valve circuit for B1 - B2 and has an additional feature of a Low Water Cut Off if you purchase the 48-201 well adaptor from Hydrolevel

Hope this helps you get the correct control. 

EDIT:

If you have a Buderus boiler that is designed for an oil burner, and it was converted to LP Gas with a Power Gas Gun Burner that operates on 120 VAC then the L7224U is the correct control for you.

109A_5

You may want to look into other products like Hydrolevel's hydrostat series if you want more control features.

https://hydrolevel.com/hydrostat/

" Honeywell L8148A aquastat . I mounted it on the supply of my 250K btu LP Fired Buderus boiler just upstream from the pump 20 years ago (and ran the end switches from my Taco Gold (571) zone valves over to it and called it good. "

The L8148 is mounted to a pipe that gets hot ?

Is the L8148's bulb in a well or mounted to a supply pipe ?

https://www.supplyhouse.com/Resideo-L8148A1017-High-Limit-Horizontal-Mount-Aquastat-Relay-8-DegreeF-differential

ccstelmo

Thanks again to all.

I don't have an explanation as to why I put the well in the supply instead of the preferred location other than that an 1-1/2" proprietary supply pipe fitting (and yes, it gets hot) came with the boiler. It had several convenient taps of varying pipe sizes for Gauge, LWCO, Relief etc. One seemed appropriate for a well. I will investigate this a little further and ensure that the well is appropriate for the capillary tube (is immersed as far as it can into the supply).

The Riello power burner does require 120 volts to run and controls the two-stage gas valve so at least I got that right.

Thanks for confirming the 8 degree differential info. At least I know what I'm shootin' for now.

ccstelmo

UPDATE FROM CCSTELMO

109A_5: Yes. The Control is mounted on a well and the bulb is immersed in the tee on the boiler supply about 8" above the boiler. Pretty much the way Ed has shown in his illustration.

Ed: Upon reflection, I mounted the aquastat on the supply pipe because of the provision of the proprietary multiple tee fitting supplied with the boiler AND because the 3/4" tap referred to in your diagram was exactly where I prefer to connect my plain steel expansion tank. (It's a great place to grab air and send it to incarceration in the tank.)

Continuing on with this saga, though, I have to confess that (because my brain is starting to fossilize) I failed to check the condition of the pump. It had failed. Discovering this was an aha moment for me but that fact still did not explain the failure of the high limit on the aquastat to shut things down at the setpoint so I replaced both pump and aquastat taking care to clean out the well and gingerly squeeze silver stuff (have you ever run into anything more obnoxious than this stuff?) into the well. I confirmed that the well reaches into the 1-1/2" boiler supply pipe. Then I fired that mother up. It took a while for everything to reach steady state operation.

1. The hi limit setpoint on the new aquastat is 15 degrees off in shutting the boiler down (per the tridicator and a separate infrared thermometer). At shut down the tridicator reveals the water temperature "coasts" another 15 degrees upward.
2. The 8-degree fixed-differential low limit does not refire the boiler until the tridicator (and the infrared thermometer) read 35 degrees below the hi limit setting.
3. At no time during this cycling does the boiler return water temperature rise above 140 degrees.
4. Physical examination of the combustion chamber reveals definite signs of condensation.

I mentioned earlier that during the heating season (there are only two seasons in St.
Elmo, Colorado, winter and August), we heat only about 25% of this 5000-sf seasonal Bed & Breakfast. Isn't this a clue?

LRCCBJ brought up the "oversizing of the boiler" subject. Basically, it seems like that's what I've got going here. Can anyone think of a scenario where this can explain ALL the symptoms I've described?

I sure do appreciate your input and hope you're not giving up on me yet.

ccstelmo

LRCCBJ

• 1. You can adjust the dial on the L8148 to reflect this difference. They are not the most accurate devices and they certainly depend on the contact between the bulb and the well. Most folks will have trouble getting sufficient amounts of the paste deep into the well where the bulb lives.

• 2. Where are you finding a Low Limit? Unless you have another aquastat connected to the 8148, it will never fire the boiler until the thermostat closes. Why do you believe you need a low limit? I believe you are probably looking at an open call from the thermostat and making conclusions on temperature based on that.

• 3. This is only possible if the aquastat is set too low AND/OR the radiation has considerable mass and the boiler cannot keep up with it. If the HL is set to 180F and the return temperature is 140F, the radiation is dissipating more energy than the boiler can produce. This is a common situation when CI radiators are cold. If excessive, the boiler needs a return water bypass so the temperature is raised by the injection of supply water.

• 4. Of course.

109A_5

With the high limit being outside the boiler on a pipe, with no water flow it can not properly detect the actual boiler temperature so it may not function as needed or intended. Example; a call for heat yet for any reason the circulator is not running.

" Physical examination of the combustion chamber reveals definite signs of condensation. "

You probably need the proper piping setup to keep the boiler water at the proper temperature.

ccstelmo

Per Honeywell Tradeline Literature supplied with the aquastat:

"A call for heat by the thermostat starts both the circulator and the burner. When boiler water temperature exceeds the high limit setting the burner circuit is broken and the circulator continues to operate until the thermostat is satisfied."

It is left unsaid, but the FIXED 8-degree differential between the hi limit and the low limit will maintain the boiler water temperature within an 8-degree range manually selected by the operator when he chooses the hi limit setting.

No part of the aquastat bulb is "outside the boiler on a pipe". The bulb is in a well that is immersed in the supply water within the supply pipe coming off the top of the boiler.

The larger question is "Why is the boiler water temperature exceeding the setting on the hi limit dial by 35 and 40 degrees before the boiler fires down?" Is this a water flow velocity through the boiler problem?

109A_5

" No part of the aquastat bulb is "outside the boiler on a pipe". The bulb is in a well that is immersed in the supply water within the supply pipe coming off the top of the boiler. "

So the bulb is outside the boiler 'in' a well that is 'in' a pipe, is that more accurate ? If so that is in the wrong location.

It needs to be in the well in the boiler not in a well in a pipe. The water temperature in the pipe may not be representative of the temperature in the boiler.

" The larger question is "Why is the boiler water temperature exceeding the setting on the hi limit dial by 35 and 40 degrees before the boiler fires down?" Is this a water flow velocity through the boiler problem? "

Assuming there is an aquastat bulb in a well inside the boiler and it is correctly installed and correctly wired to the boiler's electrical system and it once actually worked correctly, but it does not now, it is probably defective.

EdTheHeaterMan

Without circulation, that aquastat location is not the best for the safety of the boiler. There may be times that the circulator may not operate. there may also be times that the circulator can not move water thru the system because the radiators are air locked. The high limit is a critical part of the "SYSTEM" and not an after thought. there is a correct location that the manufacturer specifies. That location is based on testing and approvals by code and engineering standards that people a lot more experienced that you or me have decided on.

@ccstelmo may be one of those smarter engineers and that location on the pipe may be fine, I just would not want him designing any pressure vessel that contains a flame inside it, for my home.

Just an old man talking here.