Honeywell Aquastat function question


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Old 02-10-12, 07:43 AM
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Honeywell Aquastat function question

I have a Burnham revolution boiler with a honeywell L8148e1299 aquastat controller.

My problem is all works fine except on occasion when the aquastat shuts the gas off and the circulator is running off of the vs3000 circulator controller a relay in the aquastat turns the power to all "off" It might stay off for a minute or two then come back on in which case all returns to normal running. I can not decifer from the schematics what controls the relay in the aquastat.
 
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Old 02-10-12, 08:52 AM
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Hopefully the resident Burhnam master, Mr. RBeck can help us out with this.

As far as i understand it, the vs3000 controls an internal bypass circulator. It may be stopping or slowing down the boiler pump as needed.

The relay in the aquastat is controlled by the room thermostat, or zone valve end switches or other external controls.

Even though there is a call for heat to the aquatat the vs3000 seems to have the final say on running the internal boiler pump.

Or something like that.

The Burhnam pro's here will correct me.
But here may not be anything wrong with your system.

What are the temperature and pressure readings?

Peter
 
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Old 02-10-12, 10:15 AM
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Temperatures are running normal.
Your right about the VS3000 controlling the boiler circulator. I had to put a new temp sensor to the VAS3000 and after giving it coat of thermal grease it works as expected.

When all the thermostats stop demanding then the system goes into shutdown i.e. no power (normal)

It's when there is still a demand and the circulator is running I get normal temps and sequencing of the flame via the aquastat. this condition ran for hours yesterday.

As I said though on occasion the whole system will go into shutdown for no apparent reason for a minute or two and then comeback on. It actually doesn't hurt anything as all goes back into start-up sequencing but this shouldn't be happening when there is still a demand so I'm baffled.

I was wondering if the differential pressure switch might be in line with the Aquastat relay??

This condition doesn't occur with flame on, at least I haven't seen it do it. it only occurs while flame is off and circulator is running.
 
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Old 02-10-12, 10:41 AM
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I'm still not clear on exactly what us shutting down?
Everything totally?.

If you look at page 53 here:
http://s3.pexsupply.com/manuals/1282..._PROD_FILE.pdf
It is a ladder diagram. Fairly easy to follow.
The only thing that i can se to shut everything down is is a low water cut off. Or external wiring issues.
The VS300 as we said, will shut down the boiler pump.
There are a plethora of things that will shut the gas off.
They can be explored in more detail on page 52.
Certainly the differentail switch is in play here.

Maybe a massive down draft or exhaust fans in the house or something affecting the air pressure?

Peter
 
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Old 02-10-12, 10:54 AM
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I think I've got it. The T and TV line from the Aquastat are the boiler control lines supplied from my TEKMAR zone controllers which caries the 24vac to pull the relay up. I pulled one of the junctions and the system shut down while I was looking at it the system went on and off. What I've realized is the wire nut holding the two dissimilar wires together was a lousy connection. So what I'm going to do is solder the junction and replace the wire nut.

But while your here when I replaced the Aquastat there was no heat sink grease supplied and the old unit didn't seem to have anything on the bulb. Should I put some heatsink compoung on the bulb where it goes into the well?

It certainly made a difference with the temp sensor for the VS3000 operation.
 
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Old 02-10-12, 11:58 AM
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Hi Monty,
Controversial about the grease. It is said to dry out and turn into a hardened mess after time.
The consensus around here is as long as there is a good, firm, mechanical connection, it will be ok.

Can you tell us more about your Tekmar set up. Which model controls, etc.
I'm very interested in how it all works together and if you are satisfied with it.

Thanks,
Peter
 
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Old 02-10-12, 01:00 PM
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What I have is a Tekmar 251 and and 368
I understand that the 251 Boiler control is a relay that closes to turn boiler on and off.
Problem is understanding the logic behind the control. It appears to be controlled by the differential time setting.
I fail to get how the differential is derived. The only other sensor I have is one placed on the output of the boiler just prior to the zone pumps.

I agree about the heat sink getting stiff as it ages. That's one of the reasons I asked. It could present a big problem removing the bulb down the road, It seems to be tracking pretty consistent as it is so guess I'll leave it alone.
The compound on the temp sensor for the VS3000 sure made a big difference in how it tracked the temp and controlled the circulator speed. There was none on the original set up so didn't put any on at first. After I put on some grease I put a meter on the output to the circulator and watched how it changed the duty cycle nicely. The % LED can be misleading if you try to figure if the unit is working correctly just from watching it as the LED won't go into full on until the temp gets at or near boiling.
 

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Old 02-10-12, 02:05 PM
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Here is some info on those controls.
http://tekmarcontrols.com/media/literature/d251.pdf
http://tekmarcontrols.com/media/literature/368_d_06.pdf

There should be an outdoor sensor somewhere, connected to the 351.

Peter
 
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Old 02-10-12, 02:23 PM
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I put a meter on the output to the circulator and watched how it changed the duty cycle nicely.
You must mean an oscilloscope... you can't see duty cycle on a regular multi-meter.

I would also suggest not using the compound on the a'stat bulb... at least not as much as Honey recommends! I don't think there would be any problem putting a 'blob' in the bottom of the well, but certainly not the whole dang tube!
 
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Old 02-10-12, 04:48 PM
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Your right about not being able to see the duty cycle except you can see the resultant voltage to the circulator and watch that voltage vary as the duty cycle changes. It'll go from "slow" about 57v, up to 120 at full speed. Far better then trying to determine if the %LED is changing blink speed.

I have those manuals that you suggested and they do show the differential adjust. What I don't get is if the sensor on the output of the boiler to the system is what is read by the Tekmar for the differential temperature then it shouldn't be changing as rapidly as my symptoms are. I did crank up the differential pot. Perhaps I should choose a higher midrange temperature to stablize the boiler turn on cycle.
Yesterday when I got everything up and running with a new sensor and Aquatstat the house was cold and so the system ran for several hours without a glitch, but after the house got warm again then it began the boiler shutdown symptom when it should have been flame off and circulator running.

Everything works but it appears to be an adjustment problem now.

Any perspective here is welcomed.
 
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Old 02-10-12, 06:19 PM
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Monty, if I recall, Burnham recommends the a'stat be set at 190... I think I remember that right... probably has nothing to do with the 'issue', but wonder if you've lowered that for some reason?

I also wonder if the Tek's are messing with the VS unit? The VS wants to target 160 as it's full speed point, yes?

I wonder if someone else who is using a Rev wants to add anything to this discussion? Hmmmm?
 
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Old 02-10-12, 09:00 PM
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What I found with the old Aquastat was that it was set at 210. What happens then is the VS3000 actually doesn't reach full on until about 212 according to the temperature at the sensor. With full flow of water to all the zones the VS3000 will cause the circulator to moderate the water temperature at the output of the heat chamber so all that happens is the flame goes on and off via Aquastat hightemp relay but the output temperature of the system is slowly but steadly climbing. The output temp never reaches anything excessive like 200 so that seems to be perfectly normal.

The Tekmar cant do anything to the VS3000 as it is isolated from anything other then the 120 supply to it from the Aquastat.

No my problem is the Tek is cutting off the boiler signal at times when it should stay on. As a matter of fact I've wondered why Tek didn't take into the control system a signal from the VS3000 temp sensor to say I'm a little hot here stay on until the circulator cools me down. As it is now when the thermostats drop demand to the Tek the boiler signal just drops. That could be happening just when the heat chamber is at it's hottest point. It's probably not hot enough to really hurt anything but seems it would be prudent to bring the temp down before power shut off.

So the question is do I adjust the minimum supply temp or boiler differential and time delay? Both maybe?
 
 

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