Correcting boiler exceeding aquastat Hi setting


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Old 12-17-09, 08:38 PM
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Red face Correcting boiler exceeding aquastat Hi setting

Hi - new member, here

The short problem is that I'm trying to figure out why my boiler's aquastat doesn't appear to be reading (or reacting) to the boiler's water temperature the way it is set to. When set at a Hi of 180 the boiler temp would exceed 200 and (I'm guessing) cause pressure to exceed 30psi, resulting in pressure relief valve discharging.

I have a Slant/Fin Liberty Oil fired boiler with Honeywell aquastat, two zones of baseboard water heat (upstairs/downstairs) and Zone1 (priority) for our SuperStor SSU-45 for domestic hot water. All zones are controlled by three separate Taco circulators.

Also, I've posted basically this same info with lots of pictures to my blog here:
AJD.US: Boiler "hacking" - what's going on with my aquastat?

The direct link to the picture gallery is:
Picasa Web Albums - Aaron - furnace

This problem only started happening, unfortunately, after:
  1. the boiler was serviced (yearly maintenance under contract by our oil delivery company)
  2. our original slowly-leaking SuperStor SS-40 was replaced by our new SuperStor Ultra SSU-45
  3. I removed the jumper to cause Zone1 to be priority again to try and provide more hot water for longer showers for the wife (i added the jumper to prevent priority shortly after buying the house several years ago)

2 & 3 occurred on the same day, and 1 happened about two weeks before that...

Several days after 2 & 3, I noticed the pressure relief valve was discharging, which is when I also noticed the temperature would exceed 200 and the pressure would reach 30psi.

I first suspected the plumber hadn't bled the system properly and air expansion was causing the pressure... so I called the plumber, who came out and replaced the expansion tank (he checked and said it didn't appear to be an issue with air).

The expansion tank may have helped, but the original seemed fine to me (not full of water, pressure at valve was ~18psi which was the current boiler pressure)...

After I was watching the boiler after the plumber left, I checked out the aquastat and noticed that even though the boiler had reached 200 deg. F, the burner was still going - and the aquastat was set at a high of 180. I dialed the high down and the burner cut out...

Right now, with the low at 140, and the diff at 10, the burner appears to operate correctly - I just watched, with no zone calling for heat, the burner kicked in at 140 and off at 150. So it seems it is just the Hi adjustment that is not calibrated correctly(?)

SO.....


I have now dialed the Hi back even further (just below 160, which seems to allow it to exceed 180 by a few deg.)

My (many - sorry) questions are:
  1. Should I have restored priority? (and with priority, should the boiler now be maintaining the low temp? with just the addition/removal of the one jumper for yes/no priority, the boiler seems to go from cold-start (no priority) to maintaining low temp.... how much less efficient is this - is it necessary?
  2. What is the cause of the disconnect between Aquastat detected temp and temp gauge?
  3. is over-temp a likely cause of the overpressure? is it likely to have anything to do with the expansion tank after all (So far pressure seems to hold around 20psi now when running, so no more over-pressure)
  4. What *should* the aquastat Hi, Low and differential be set at for a system like this?
  5. I'd like to eventually replace the aquastat with a more intelligent one that takes outside temp into account - any suggestions? Is it worth it?

Thanks!
Aaron
 

Last edited by ADaubman; 12-17-09 at 08:52 PM. Reason: added low/diff data
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Old 12-18-09, 02:38 PM
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Thumbs up Pseudo cold-start

Originally Posted by linuxrunner78 View Post
Would it be ok to lower the LO temp setting on the triple aquastat? A pseudo cold-start setting? The ultimate goal here is to provide more hot water but reducing oil usage would be a good benefit if its possible.
linuxrunner78: I have pretty much the same setup you are installing now (three zones, two for first/second floor baseboard HW heat, and a third for Indirect SuperStor Ultra 45 gallon tank - only real difference is I have three different Taco circulators rather than zone valves)

I've also been wondering the same thing - is there a control (I've been passively following the Intellicon discussion, and have also taken a look at the Beckett HeatManager and AquaSmart Boiler Control) that would more intelligently operate one's aquastat settings?

E.g. I've been considering going back to a pure cold-start, since our shower is *mostly* used in the morning, as long as I set our programmable thermostats to kick in an hour or so before we usually get up, the boiler should have recovered from the low-night temp settings and be able to produce hot water for the shower (especially since the SuperStor Ultra is supposed to lose less than 1degF/hr)... but then, how do you deal with mid-day or weekend showers? (need a programmable aquastat on my SuperStor?)
  1. Is there a common best-practice for this sort of thing?
  2. Are there some common-sense calculations one can do to figure out where the knee in the curve would be for turning down the low, or going to cold-start?
  3. How do you determine if a replacement Honeywell/Beckett aquastat or a Non-snake-oil-addon-Intellicon-addon-type-device would be a benefit?


I'm asking (along with probably too many other questions) the same thing here, complete with pictures of my current boiler/aquastat setup:
AJD.US - Aaron J. Daubman - Life, etc...: Boiler "hacking" - what's going on with my aquastat?

Thanks again,
Aaron
 

Last edited by ADaubman; 12-18-09 at 02:38 PM. Reason: minor spelling correction
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Old 12-18-09, 04:26 PM
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Smile Sorry for hijacking - more aquastat setting questions

Originally Posted by NJ Trooper View Post
Aaron, I'd like not to see the OP's thread 'hijacked', in spite of the relevance... so, I'm going to move your post into the thread that you started with some other questions... check in there for replies...
Whoops sorry... didn't mean to hijack - thanks for moving it over with my other questions... and thanks for your vigilant moderation and helpful replies to so many different threads (I've been trying to go through all the past threads looking for tips and very frequently see the most useful ones coming from 'NJ Trooper')

On a relavant note, what was your thought process behind recommending that linuxrunner78 turn his LO all the way down, and even eventually consider going to cold-start?

Thanks,
Aaron
 
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Old 12-18-09, 11:43 PM
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Hi Aaron, I intended to answer your posts at length ... but as you probably know we're supposedly getting slammed with the white stuff this weekend... so, I'm not going to have much time at the computer next couple days.

There's a lot to go into with your posts! and a lot of answers. But I'm up to the task if you can wait a bit... others may jump in and help too ( I hope!)

You didn't really hijack, your questions more or less 'fit', it's just that it often happens that it gets confusing trying to keep continuity in a thread if there are two persons with questions in one... that's why I moved it.

what was your thought process behind recommending that linuxrunner78 turn his LO all the way down, and even eventually consider going to cold-start?
When running an indirect water heater, there is nothing really to be gained by keeping the boiler warm. There is an aquastat control on the indirect that is wired to call for heat on an 'as needed' basis, so that the boiler will fire up and meet the hot water demand only when the tank cools.

Since indirects ARE so well inulated, chances are pretty good that the unit won't need to fire up the boiler very often at all in order to maintain the temp.
 
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Old 12-18-09, 11:54 PM
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When you say that the temp on the boiler goes to like 200 with the a'stat set at 180... is that temp being reached AFTER the heat call is satisfied and the burner and circ shut down?

If so, it could be 'heat soak', where the hot cast iron of the boiler continues to transfer it's heat to the water when the pump is stopped. The water temp will normally coast upward quite a bit when this happens. It's 'normal'.

If the setpoint is exceeded while the pumps and burner are running, it's a different story. There could be a few reasons for this.

1. Aquastats aren't terribly accurate... as long as the setpoint is REPEATABLE though, the absolute accuracy is not really an issue. You can just ignore the dial markings, and set to the temp you are looking for.

2. The temp gauge might not be accurate, or sensing the temp at a different location inside the boiler, which could be cooler or hotter than the location of the aquastat 'bulb'.

3. The aquastat bulb may not be inserted fully into the well, or is a loose fit inside the well.

4. Other reasons I may have forgotten!
 
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Old 12-19-09, 12:01 AM
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Pressure problems may only be indirectly related to boiler temperature, and air in the system will never create an overpressure condition... just the opposite in fact.

Water can't be compressed, but air can.

Systems need enough air in the system to allow the water to expand as it is heated without overpressuring. The water doesn't care 'where' that air is...

but, it's SUPPOSED to be in the expansion tank, and can cause other problems if it is elsewhere.

Expansion tanks are sized such that they will take up the expanded water over a certain temperature range... if the tank is not quite large enough, sometimes the 'extra' expansion of the water up to 200 degrees from say 180 might be enough to push the pressure over 30... but usually there is enough reserve capacity.

It appears that the new expansion tank solved the over pressure problem?
 
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Old 12-19-09, 12:07 AM
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Should I have restored priority? (and with priority, should the boiler now be maintaining the low temp? with just the addition/removal of the one jumper for yes/no priority, the boiler seems to go from cold-start (no priority) to maintaining low temp.... how much less efficient is this - is it necessary?
If your boiler is not large enough to heat the indirect AND the home at the same time, answer is yes. If the boiler is sized closely to the heat loss of the home, under some conditions there may not be enough boiler capacity to do BOTH at the same time, thus the priority option.

Which 'jumper' are you talking about? Is there a control panel of some sort installed? What is it?

Priority settings should have no control over warm/cold start. That's a function of the boiler aquastat.

Tell us a bit more about the controls on the boiler... make/model of the aquastat, and any other controls attached.

Using a warm start system is wasteful IMHO. Keeping a boiler warm 24/7 costs $$$. Warm start is usually only used when there is a 'tankless coil' in the boiler which supplies the domestic hot water. There is no need for this with an indirect.
 
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Old 12-19-09, 12:20 AM
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# What *should* the aquastat Hi, Low and differential be set at for a system like this?
# I'd like to eventually replace the aquastat with a more intelligent one that takes outside temp into account - any suggestions? Is it worth it?
The HIGH setting should be high enough that the home is properly heated... but never low enough that the return water coming back from the system is cool enough that it causes flue gas condensation on the fire side of the boiler. 180 is considered 'normal'. You may get by with less, but in general that setting should be 160 or above. The boiler will only get as hot as it needs to in order to heat the home. Since you are running an indirect water heater, I would say to leave it at 180, as this will allow faster recovery times on the water heater.

The LOW setting and DIFF work together to keep the boiler warm. If you were using the 'tankless coil' inside the boiler you would want the LOW to be at least 140 and the DIFF around 20. Since you have the indirect, there is no reason to run it that high. Turn it all the way down as per other posts, and previously mentioned reasons.

The NEWEST VERSION of the Honeywell L7224U aquastat has an available Outdoor Reset module, which will adjust the boiler temp based on outdoor temps... it also has a Low limit circuit that can be turned on and off.

OLDER versions of the same control are not able to use the new ODR module.

With a standard efficiency boiler such as you have, you can NOT do what they call FULL reset. FULL reset would allow the boiler temperature to only supply the temp water needed to heat the home, which could be quite low depending on the outdoor temp. You can't run your boiler temp that low because of the condensation problem... so you could only do PARTIAL ODR, which will limit the LOW temperature to something around 140-150. This would limit savings, but protect the boiler from acid corrosion caused by flue gas condensation.

Boilers that are specifically designed to CONDENSE can of course be run all the way down to room temp if desired... without damage... because the materials used aren't subject to corrosion from the acid, and they are designed to collect and dispose of the condensate (after it's neutralized).
 
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Old 12-19-09, 12:27 AM
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Looking at some of your pics...

What is up with that aquastat all caddy wompus like that? they are usually installed either vertically or horizontally... never seen one installed at a 45 like yours is... that tellme that that someone has been diddling with it, and might lend some credence to the idea that the bulb is improperly inserted. It will work at any angle, that's not the issue, it's just the fact that it's obviously been 'messed with' by someone previously that has me bugged.

The LOW / HIGH settngs shown are getting a bit too close together... they should never be set closer than 20 degrees apart.

And I answered the question I asked about the boiler controls by looking at the pics also... probly shoulda done that first.
 
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Old 12-19-09, 02:06 AM
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The aquastat is on a slant because someone couldn't be bothered to properly run the flexible conduits! The one going to the burner (top one) is even broken. Both conduits should have 90 degree fittings.
 
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Old 12-19-09, 09:29 AM
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I'm also willing to bet that there isn't an 'anti-short bushing' in sight on one of the cable ends, and it appears that there is no ground wire running to the burner (ground wire clipped short).

Also... it appears as if the power cable into the aquastat doesn't even have the correct connector on it! That connector with the two screws and the clamp is NOT from metallic sheathed flexible conduit, it is for NON metallic cable ONLY.

Aaron, look inside of the cable connectors and see if you can see and signs of a red plastic 'bushing' around the cut end of the metal cable sheath.

I would do some rework on that wiring to get it up to code...
 
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Old 12-20-09, 05:41 PM
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Replies - and thanks

Thanks for all the replies so far, NJ Trooper... I hope the snow didn't hit you too hard - we got a decent amount up here on the MA/NH border, but it was at least very light snow.

Anyway, I have corrected over-pressure condition, but since I replaced the expansion tank and lowered the HI setting I'm not sure which (if not a combination of both) fixed the problem.

To answer an earlier question, it appears that the Aquastat and gauge are both pretty accurate - with the low set at 140, the burner ignites right about 140 on the gauge, and with the diff at 10, stops right around 150 (when nothing is calling). It is only the HI that seems to be off by ~20deg F (e.g. the previous 180 allowed it to rise just above 200, and the current 160 allows it to rise just above 180).

Finally, when it was reaching just over 200 it was when a zone was still calling and the burner was still firing, it doesn't seem to suffer much from heat soak, probably due to its small size.

Woah - when replying I just noticed there were many more replies than were showing up in thread view - I'll read through all of these and add more replies.

Thanks again,
Aaron
 
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Old 12-20-09, 06:06 PM
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Jumper Settings

Originally Posted by NJ Trooper View Post
If your boiler is not large enough to heat the indirect AND the home at the same time, answer is yes. If the boiler is sized closely to the heat loss of the home, under some conditions there may not be enough boiler capacity to do BOTH at the same time, thus the priority option.

Which 'jumper' are you talking about? Is there a control panel of some sort installed? What is it?

Priority settings should have no control over warm/cold start. That's a function of the boiler aquastat.
Ok, looking at the wiring diagram here:
Picasa Web Albums - Aaron

I should be following the left-side (since I am not using a tankless setup)

As you can see from the current wiring:
Picasa Web Albums - Aaron

It should be set up as directed, except the P / ZC jumper has been removed to provide priority for Zone 1 (the indirect).

What I'm not understanding is:
  1. With P/ZC connected there is no zone priority (as expected) and the boiler is cold-start
  2. With P/ZC not connected the boiler switches to warm-start (unexpected) and there is zone1 priority

This really bugs me since it seems (to me at least) to be the worst possible combination. If I don't have priority, I would benefit from warm-start, since if all zones start calling at once at least there's some thermal capacitance to draw from. Along the same lines, with priority, cold start should be fine since I'm guaranteed to only be running the smallest zone (zone 1 for the indirect) which would allow the boiler to heat up faster to heat the water as needed...

Any suggestions as to why it would function like this? Is this expected behavior? Is it possible the Aquastst itself is wired incorrectly (or can have warm-start disabled some other way than disabling priority)? X1 and ZR are correctly wired to TT on the aquastat.

Is it possible this has something to do with the poor job done by whoever installed the aquastat originally?

Thanks again,
Aaron
 

Last edited by ADaubman; 12-20-09 at 06:08 PM. Reason: correct list entry
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Old 12-22-09, 04:54 PM
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With P/ZC not connected the boiler switches to warm-start (unexpected)
There's no way this can happen that I can think of! All the removal of that jumper in the 503 panel does is prevent any of the heating zones from calling the boiler, or running their zone circs...

The 8124 aquastat is what provides the warm start function... that's what the LOW and DIFF settings are.

In other words, you should be able to disconnect the T T wires from the 503 panel to the aquastat and the boiler would STILL follow the LOW settings on the aquastat. With the triple aquastat that you have, as long as the power is on, the boiler should NEVER go cold.

Is it possible this has something to do with the poor job done by whoever installed the aquastat originally?
Maybe... I guess so... but before I judged, I would want to do some other testing to be sure I was seeing what I thought I was seeing.

Why not do that? Remove the T T wire from the aquastat, and see if it goes cold. If it DOES, then something is wrong with the aquastat itself. (not unlikely)
 
 

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