I have an oil-fired burner system, which runs a mixture of glycol for radiator heating. We have five zones and a separate water storage tank. The water tank does not mix with the glycol. It contains a coil based system for warning the water. The problem I have is this: with all zone valves operated by programmable thermostats, they are turning down at 10pm. So at this point, there's nothing that's driving a valve to open. However, the burner continues to cut in every 15 minutes, and fires up for 2-3 minutes, and then shuts off again.

It seems to me that it's just cutting in to keep the glycol lines at a certain temperature, in anticipates of a zone valve opening. The system also has an infinite loop which runs to our external garage and back.

I'm not sure what to do, but it seems completely inefficient for a boiler to be cutting in and burning 20% of the time needlessly (i.e. there are no zones requesting heat and the hot water is not being consumed).

IS there a way to regulate the burner the same way that we regulate the zone valves using a programmable thermostat? Or is this normal to behave this way?

Any / all help is greatly appreciated.

Thanks!

 

It could be that the boiler controls are set up as a "warm start", which means that the boiler water temp. is not allowed to fall below a certain set level (LOW LIMIT). In a nutshell, the boiler is kept warm all of the time, regardless of whether there is a call for heat or hot water.

By contrast, a "cold start" boiler is allowed to cool down to room temperature so long as there is no call for heat or hot water.

Warm start boilers are found mostly in cases where the boiler itself makes the domestic hot water (DHW) for the home by virtue of a copper coil located inside the boiler. The coil must have hot boiler water surrounding it at all times in order to be able to deliver DHW on demand. Maybe your boiler originally had such a coil, and that is why it is set up as a warm start.

If you could better describe and even post pics of your boiler piping and controls, we can tell you if it is indeed a warm start.

Since you currently have a DHW storage tank, it's possible that you could convert the boiler to a cold start, but more information is needed before we get there. In some cases it is not advisable to do the conversion.

 

Please tell us the MAKE and MODEL of your boiler.

Find the AQUASTAT installed on the boiler and tell us the MAKE and MODEL of that as well. The aquastat is 'usually' a gray Honeywell box, about 4" x 6". There are other makes as well...

Is this a 'new to you' system that perhaps you've just moved into the home? Or, has it always done this? Or, is this a new development that you've just noticed?

Ditto the request for pics.

 

Rockledge:

Yes, that makes complete sense. The water storage is separate from the boiler itself, and the boiler does have coils I believe, although I've never taken the covers off of it to confirm. It has a separate glycol line that is heated for the radiant zones, and that glycol is then circulated to a separate coiled storage tank to heat the DHW. So I can completely understand the need for a warm start, when our temps are down to -35 Celsius in the dead of winter. But in spring/fall, it doesn't make sense at all for the boiler to be running all the time like this. I sat in front of the boiler the other night to try and figure out what was setting it off every 15 minutes, and finally figured out that once the temperature falls back to 180 degrees, it kicks in, then it warms up to almost 200 degrees and shuts off... regardless of if a zone valve is open.

NJ Trooper:

Sorry for the delayed reply. I don't get automatic emails or notifications that a reply had been submitted to my original question. Sorry.

I will take a few photos tomorrow and send along the make/model, etc.

Thanks again and stay tuned.

 

The forum won't automatically 'subscribe' you to a thread, even your own. I am not sure but there may be a checkbox in your profile settings that allow you to change that behavior. If you DID subscribe to the thread, I've heard that there have been some problems lately with that...

It sounds to me like the settings in your aquastat are whacked... even if you DO need to run a warm start, it seems to me that 180-200 is EXTREMELY high for those settings!

Waiting for pics...

And, if you are so inclined, slide the cover off the aquastat box (which I'm betting is an 8124 model) and let us know what the HIGH, LOW, and DIFF dials are set to.

 

Looks like the boiler is a Buderus Logana, with a Metron 5M burner. I'm not exactly sure what the Aquastat is that you're referring to, but I'm assuming it's the black box which I uncovered for the photo here. I also took some photos of the zone valves and water heater. Not sure if this helps any.

 

Here are a few more photos including the zone valves.

 

Spring through fall you might lower the aquastat settings to turn on around 140 and turn off around 160.

Even with the same spread, at the lower settings closer to (although still somewhat above) room temperature the boiler won't cycle on as frequently.

You might wrap the boiler (don't cover any access hatches or vent holes) with fiber glass insulation batts or panels without plastic or paper facing.

 

The black box is a low water cutoff that kills power to the entire system if the water level falls below the probe.
I don't see an aquastat. Inside the Mectron?

 

The grey elongated box on top of the boiler is an aquastat.

 

Not a good idea to wrap the boiler in insulation.

The 'Mectron' is a Riello brand oil burner.

As Guy said, the black box is a Low Water Cut Off.

You actually have TWO aquastats, one on top of the boiler and another in the pipe further back near the flue pipe.

Without knowing how those are wired together, it's impossible to say why your boiler is acting the way it is.

Can you see the temperature settings on the two gray aquastat boxes?

That Yell-ange color thing is your water heater?

 

My bad. I thought "aquastat" referred to a control with several functions and single-setting boxes were just "limits". Is aquastat a generic or trademarked term?

 

I think it's a 'generic' term. Nope... I'm wrong...

I guess the trademark is so old that it's now used like a band-aid!

An aquastat is a control that performs a function based on water temperature.

The most basic type is what is shown in the pics... a temp probe, setpoint dial, and switch contacts. They are all more or less limit switches in the strictest sense of the term.

The aquastats for boiler control are 'integrated' devices, in that the 'limit' switch controls relays that perform different functions based on what it's designed to do.

The newest 'aquastats' even include LWCO probes, yet more integration.

But, at the root of it all is a temperature probe and a switch.

 

The black box, has a little set of "arms" in it. You can see them at the very bottom left. That's what clicks on/off (i.e. closes the connection), once the temperature drops to 180 degrees and the boiler kicks in, and then it opens the connection at 200 degrees, and shuts off again. The "aquastat" you're referring to are the temperature control boxes I guess (two grey boxes - one on the boiler and the other just behind). Those are set at 180 degrees (the one on the boiler) and 200 degrees (the one just behind the boiler). Without having opened up the wiring of them, it appears to me that they are both wired to the black box, and that they are both controlling the low/high limits.

I can certainly lower the limits to 140 and 160, but it will still keep going on and off, when I really don't want it to unless one of the zone valves have opened up.

I guess at this point what I really need to determine is, whether or not there is a way to set the system up so that it can "check" before turning on at the 180 degree mark, whether or not one of the zone valves is open, and only then fire up - if no zone is open, then let the system continuing cooling down until one does open up.

I should also say that I live in a very cold climate, most of the year, so I can certainly understand why the system might have been setup the way it was. Temperatures will soon dip below freezing in early to mid October, and by the time mid-November comes around, it will be hitting close to -30 celcius. Dec and Jan average -30 to -35, Feb around -25 and then starts warming up again rapidly after February.

Anyway, I really appreciate all of your feedback, so please keep your ideas coming!! Many thanks. Dave

 

Yes, the yellow "box" is the water heater. Inside is a round cylindrical container, which contains the "wrap" of heating coils around the actual water storage tank. The glycol cycles through that, whenever the zone opens, and heats the storage tank, far as I know.

 

The "arms" you refer to are a 120V power relay. I'm not an expert and am only familiar with my gas-fired boiler but I think the low water safety should not be "daisy chained" with other limits. That relay is supposed to always be pulled in (on) unless the water level falls below the probe (the white insulator with the white wire on it). For that much water to leak out would be a catastrophic failure so the LWCO is a last-ditch safety that prevents the boiler from firing up on an empty heat exchanger, which could cause an explosion.

Your other aquastats are wired in series with the LWCO and are operating on 120V power. That doesn't sound right to me. It seems to be working but is rather crude and inefficient to keep the boiler cycling between 180-200 all year long when there's no demand from the thermostats.

Others with more knowledge will chime in and correct or expand on my post.

 

Maybe so [the thing with the arms is called a 'relay'] that the relay is energizing and de-energizing with the boiler temperature, but it is important to understand that the relay is NOT what is CONTROLLING the temperature. If that relay is working on and off with the boiler temperature, it is because those two aquastats are 'telling' it to, due to the way the system is wired. I think that you 'get' this already, just saying in case you don't.

My thinking also, one is the high and one is the low.

I can also understand why, if your climate is that cold. I've heard that 'up there' are many systems set up as yours is. I'm not going to suggest that you convert the boiler to a cold start at all... because if there is a real 'reason' for it to be set up like that, I will not be the one to put you in a right pickle...

On the other hand, 180-200 in my OPINION (and maybe not a good one because I've never lived or worked in an area that cold) is that those temps are crazy hot!

I understand your quest to save fuel and money, and lowering those temps might be good advice... but before giving that advice it would be imperative that one understand ALL the possible ramifications that lowering them might bring.

You CERTAINLY do NOT want something freezing up in the D.O.W. !

It would and could be an acceptable wiring scheme... as long as it would absolutely prevent the boiler firing in the event of a LW condition.

I would like to look at the manual for that LWCO... I presume that the schematic diagram picture is on the inside of that cover... It's a McDonnell / Miller model 900, correct?

 

There appears to be some low quality, shoddy workmanship in the wiring of that LWCO.

Locknut missing on one of the wire connectors, wire nuts not fully covering the exposed sections of the wiring, etc...

Here's the PDF file for that LWCO:

http://documentlibrary.xylemappliedw...11/05/7155.pdf

 

Do oil burners commonly use 120V controls rather than 24V?

 

If that relay is going on and off with the aquastat controls, then I would have to say that it is probably not wired correctly.

It would seem that the two hi/lo aquastats are controlling the 120VAC circuit to the LWCO and turning IT on and off, along with the burner... when in fact, the LWCO should be wired so that it's supply voltage is constant. As guy said, the relay should NOT be cutting in and out with the aquastat signals.

The aquastats should be wired into the burner circuit AFTER the LWCO.

It WILL (and obviously it DOES) work the way it is currently wired, but it is not per the (rather vague) installation instructions.

Now is not the time to start a re-wiring project on your boiler in case you are so inclined.

Is it true that there are only two seasons in Canada?
July and Hockey?

 

Typically, yes.

Motor runs on 120 so easiest way to do.

 

Thanks to everyone who has replied thus far (NJ Tripper, guy48065, tomf63 and AlanJ). Very much appreciated.

 

I took the covers off both Aquastats this evening, and the one directly on top of the boiler is actually set to 170 degrees, and there's a smaller "dial" under the bottom of the wiring, which is set at 25. On the 2nd Aquastat which is closer to the chimney stack, it is set at 195, and the small dial underneath is set at 15. What exactly are those secondary dials on the Aquastat for and do those settings of 25 and 15 have any meaning?

I'm thinking that the 170 with a 25 is telling it to cut in at 170 and heat up 25, and the 2nd is set at the same temp (i.e. 195) to cut off and cool down 15 perhaps?? but that's just guestimation only!!

Thanks again. And yes, there are two seasons here... July and Hockey, or cold and COLDER!! :-)

Actually, it's not that bad - summers are amazing, but they're short.

 

guy mentions that the white probe is the LWCO "switch" to safeguard against low water levels, however, if you notice where that LWCO control box is situated in the overall setup, it's at the highest point and is not on the actual boiler itself - so I don't think it's setup to check low water levels. Wouldn't it have to be at some level within the height of the actual boiler to check the water level, or does it work based on water pressure within the pipes only, and not based on a "height" of water level? Just curious - love what I'm learning from all this, by the way! thanks again.

 

thanks for posting the link to the PDF file for the LWCO! very interesting

 

Your idea of what the smaller 'dial' does is more or less correct... those are called the 'differential' settings and they control the 'range' of operation of the aquastat.

When it gets confusing is when there are TWO control.

It is possible that they are not 'high' and 'low' individual controls.

One control could be doing the 'high' AND the 'low', by means of the setpoint in conjunction with the differential.

The other could be what is called an 'auxiliary' high limit which would only come into play if the main operating control failed. It may be (and in fact probably is) this... a 'redundant' back up control.

But, without knowing exactly how the thing is wired, we can't know for sure.

One thing that you CAN do to test this theory is to turn ONLY the 170° setting down to say 150° or so, leaving the differential at 25°, grab a LaBatt's (ok, make it three) and camp out in front of the boiler and observe. If you now see the boiler cutting ON at around 150 and OFF at around 175, that would more or less prove my theory that the back one is an auxiliary high limit.

You actually want the LWCO to be slightly ABOVE the boiler.

That probe operates on electrical conductivity of the water, it's not a pressure switch.

Boiler pipes are always filled with water. As long as they are, the probe will sense that, and allow the relay to operate the boiler.

If the water were to drop below the level of the probe, the boiler would be cut off. We WANT the boiler to be cut off BEFORE it's run dry, thus the control needs to be slightly above the level of the top of the boiler.

 

Thanks NJ Trooper! I'll do the 3 beer deal and try this and let you know how it goes. PRobably won't be until Friday though. I decided tonight to dial down the 170 to 150 and I also did the backup one as well (195 down to 175). Got 'er warming up now and will see if it makes any diference. But I think it will be exactly as what was happening last week. Stay tuned! And thanks again.

 

By dialing both down, you won't know if one is auxiliary and one the operating control though.

Do one first and observe, then do the other, later. I don't think you will actually notice any difference dialing the back one down lower, unless you lower it BELOW the front one... in that case it would take control because the boiler would hit IT's limit first.

I don't think it will be exactly... it should be 20° lower. It will still cycle, but at a lower temperature.

 

interestingly enough, it does still cycle, but at a much different pace - and this is by lowering both. I didn't get your note until tonight!

So by lowering both, as I mentioned I would, the cycling is now taking place at 17 minute intervals and is on for the same amount of time (2-3 minutes). That's just more than double the space between intervals though... 20 degrees higher and it was turning on at 8 minute intervals. The only thing different, is that the outside ambient temperature has been about 4-5 degrees warmer in the days the last few days, so it could simply be that the system is not cooling down as fast as it was last week. I'll have to buy a few beers tomorrow and plunk my a$$ down in front of the boiler. I'll turn the back one back up to 195 and leave the front one down at 150 and see what happens then. Thanks again!

 

It makes sense that not being as hot would slow the heat loss.

The hotter a mass is, the faster it will lose heat. In physics they call it the 'driving force'. It has to do with the difference in temperature between the mass and it's surroundings.