Boiler Possibly Short Cycling--(long post, sorry)

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Old 10-23-08, 08:26 AM
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Boiler Possibly Short Cycling--(long post, sorry)

Here's what i have.

Burnham V7 boiler with 2 zones. One zone for baseboard heat in small 3 bedroom well insulated ranch. second zone for indirect 41 gallon amtrol hot water tank. The hot water tank was recently replaced as the old one developed a leak because the bottle had failed.

I had not had the boiler cleaned/serviced since I moved into the house 3 years ago. I know I should have, but I'm a procrastinator, what can I say. I finally got an annual service contract with my oil company, and had someone out to service it. He cleaned the boiler, and did a "tune up". Had to call him back 2 weeks later, as I noticed black smoke out the chimney. Apparently, the "air vents" got bumped and were inadvertantly closed. he said I probably bumped them when I was installing my new hot water tank. That's certainly plausible, but I'm not sure why he didn't secure the set screw the first time he did it, which should have prevented them from moving if bumped. In any event, he cleaned once more and reset them.

The technician did several things I did not care for. First, to run the boiler for servicing, he manually opened the zone valve on the zone for the hot water heater. As a result, he let my brand new tank get too hot, and the tank spit out an error code (it does so if water temp goes over 150). I happened to go downstairs when he did this and he asked me to look in the book to determine what the code meant. I opened the hot water on my basement sink, and let it run for a few minutes and that took care of the error. he claims he did that so he wouldn't make my house hot (was a warm day) but it struck me as dumb. The relief valve didn't blow, so I'm guessing it didn't go too much over 150, and hopefully didn't hurt anything, but still it seemed like a bad thing for a "pro" to do.

Next he adjusted the dials in my aquastat. I never saw where they were set initially, but he recomended the high setting be set to 180. Seemd to make sense since I've seen the gauge on the boiler top out at 180 in the past. Well, what I didn't realize is, apparantly the high on the aquastat was initially set to 145. However, the reason why it was set so low is because my aquastat is off by 35 degrees. How do i know you ask? Because this past weekend temps dropped significantly, so I used the heat for the first time. I checked the boiler after it ran for a while, and it had spewed all over my basement through the relief valve. Temp was at 215 and pressure around 30 psi! In any event, after much testing and research, I found that it is simply a case of the aquastat not being accurate with the temp. I'm guessing either the probe isn't seated, or no gel was used on it when it was inserted. Even though it's not accurate, it's very consistent. With the high set at 145 it kicks off at 180 degrees every time. So after adjusting the aquastat the heat runs at the appropriate temps. Needless to say, the tech didn't bother to watch it cycle otherwise HE would have caught this.

However, after I figured this out, I noticed it was still running very high psi. at 180 degrees, psi hit 30 and relief valve opened a little. So back to the drawing board. Likely culprit, expansion tank. Checked the air valve, and it it leaks water. So I replaced the expansion tank, and now the pressure is 12 psi cold and 19-20 psi at 180 degrees. so that's settled.

Now, last night I had a fairly long call for heat. I observed the boilers performance. The temps and psi were fine. However what I'm noticing, is the boiler is hitting the high limit really fast. For example, it was probably around 40-45 degrees out and the house temp was 64. Set thermostat to 68. The boiler kicked on and ran up to the 180 high limit and shut off. Circulator kept running as it should, and once the temp dropped 10 degrees, the boiler kicked back on. This repeated several times until the house temp hit the called for 68 degrees. What i noticed is, the boiler climbed up to the high limit very quickly. average run time seemed to be around 2 minutes, give or take 10 seconds. Then just the circulator would run for several minutes while it dropped through the 10 degree differental, an dit would then repeat.

Ok, finally, here are my questions:

1. Should I be concerned about the fact that my new tank was heated a bit over 150 degrees?
2. Is it dangerous to leave the aquastat as it is (set 35 degrees lower to compensate for it's innaccuracy)? Would it make more sense for me to try and see if it is just that the probe isn't seated, or should I just bite the bullet and replace
it?
3. Is the fact that my boiler is running up so quick on a call for heat going to lower my efficiency? I know as part of his service, he replaced the nozzle. could it be that the old nozzle was restricted, and the new one is just flowing more oil, hence heating faster? Or, perheps he replaced the nozzle with the next size? I wouldn't think that would be done, but who knows given the other things he did.
4. Could the fact that the boiler heated so hot have caused the expansion tank failure? Expansion tank is rated to 240 degrees, but it was 8 years old.

Worth noting, before the events of the past few weeks I knew almost NOTHING about how my heating system worked. I'm a pretty handy guy, but this is my first home. As frustrating as these events have been/are, at least I'm learning alot.

Also, thanks to Grady and NJ Trooper. Most of my troubleshooting/learning thus far has been from reading their responses to other posts on this site.
 
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Old 10-23-08, 11:32 AM
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You should definitely change the aquastat if you are sure it is malfunctioning. It is a safety device to kep your boiler from EXPLODING should the relief valve stick or malfunction. Either way it should be replaced ASAP as even if the relief valve works properly you could still end up with a flood of steaming hot water. My 2 cents--good luck---
 
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Old 10-23-08, 05:14 PM
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1. Should I be concerned about the fact that my new tank was heated a bit over 150 degrees?
No, I don't think so.

2. Is it dangerous to leave the aquastat as it is (set 35 degrees lower to compensate for it's innaccuracy)?
Same answer.

3. Is the fact that my boiler is running up so quick on a call for heat going to lower my efficiency?
No... but a few thoughts here...

First, I'd like to know if there is a BYPASS pipe on the boiler. Take a look where the supply and return pipes connect to see if there is a 'cross connection' between them, with some valves. Better yet, do the photobucket thing. (I'm sure you've seen the instructions how-to!)

If there is an improperly adjusted bypass valve, you might see this behaviour... and you're SURE it used to take longer ?

The other thing is that since the boiler hadn't been cleaned in a while, if the guy did a decent job cleaning it out, it's possible that the internal heat transfer is just that much better.

But, from stone cold to 180 in a matter of 2 minutes, that does seem fast ... 5-7 minutes seems more likely.

I'm not sure that I would trust the temperature gauge as an absolute indicator of the boiler temp ... you might want to verify it (or just go ahead and replace it).

Let's see the pics then talk.

4. Could the fact that the boiler heated so hot have caused the expansion tank failure?
Probably not... but not absolute. Eight years ain't a bad run for a tank, but I've seen them go lots longer. The less that the bladder flexes, the longer it will last. So, proper maintenance of the air charge will increase the longevity. I recommend checking the air charge yearly as a PM item. I know that you've read the posts and know how to check the pressure properly... once a year.

Is the expansion tank a '30' size ? 8 PSI actually seems like a lot for your type system. Point of reference, my system only runs up about 4-5 PSI from cold to 180... I'm wondering if your pressure gauge is 'true' ... again, verify... if you do replace the temp gauge, you'll get a new pressure gauge in the deal.

The other item that I advocate as a PM item is the pressure relief valve. Five years.

I wouldn't worry about the boiler blowing up.
 
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Old 10-24-08, 08:38 PM
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Thanks for the replies. Sorry for the delay. I've been preoccupied with the transmisison failure of my car. When it rains it pours I guess.

OK, so the aquastat needs to be replaced. It would be easiest to go with the same one, L8124C. However, I would love to have one that has a higher differential on the upper limit. Seems like most have a built in 10 degree diff, like this on though. Any thoughts? My thinking was with a bigger diff., I could extend my burn time on a call for heat. Just a thought.

I don't have a bypass pipe. I will try and get some pics up. I'm sure it's heating up faster now, but not sure by how much. It certainly seems possible that cleaning it could have improved the heat transfer, as it was well overdue for a cleaning.


To clarify, it's not going from stone cold to 180 in 2 min. I don't know how long it took to go from cold to 180. But, on a steady call for heat, once it gets to 180 and the boiler kicks off and drops through the 10 degree differential, it only takes 2 minutes max to heat back up to 180. Maybe that's normal??? I really don't know how long it should cycle in that circumstance.

I think I'll probably just replace the gauge. I'm sure it's the original. My gut tells me it's close to accurate though. I believe my relief valve is supposed to go at 30 psi, and the gauge was at 31 or 32 when it started peeing. Of course the valve might not be exact either so who knows. Speaking of which, a replacement every 5 years and an occaisional check on that valve seems like a good idea. Of course, this whole encounter tested the relief valve for me, and on the first go round I did have a fair amount of hot water spewed across the basement. I would hate to think about what could have happened had the valve failed.

The tank is a model 30. I also have an st-12 on the cold supply for the hot water tank. It has failed as well. I'm thinking that they were probably just neglected by the previous owner which caused the failures. I'll be replacing that one tomorrow morning before I go pick up my car and try and get the transmission to slip it's way back to my house. I read that it's best to pressurize the tank to match the incoming water pressure, is that accurate?

Thanks for the help.
 
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Old 10-24-08, 09:23 PM
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I don't see any reason to replace the aquastat. It won't cause the boiler to blow up, that's the job of the relief valve.

If you wanted to try a wider differential though, the L7224U will replace your 8124, and has an adjustable diff on the high limit from 5 to 20 degrees... take a look here:

L7224 aquastat

http://www.patriot-supply.com/produc...witem.cfm/8069

I think that 2 minute burn to go from 170 to 180 is entirely normal.

If you feel comfortable that the gauge is functioning properly, why change it ?

With your clarifications, I believe the system is running fine, no need to do anything. Change the a'stat if you wish to get a wider diff...

Yes, the expansion tank on the water heater should match the nominal water system pressure, or a few PSI above it.
 
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Old 10-24-08, 10:00 PM
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Ah, I misunderstood your response to the aquastat. I thought by same answer you meant same as the previous response by Mikegct. Now I understand. I like your answer better, it's $159 cheaper haha. If 2 minutes seems normal, then I'll leave well enough alone.

Now, if you can troubleshoot the slipping transmission on my Honda, I'll be set.

Thanks for all the help!Beer 4U2
 
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Old 10-24-08, 10:47 PM
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Now, if you can troubleshoot the slipping transmission on my Honda, I'll be set.
I might be able to, but that would cost ya !

Beer 4U2
 
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Old 10-25-08, 03:57 AM
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Since run times do affect efficiency if you are really concerned about that there are kits available to reduce the firing rate of a V7. It is nothing more than a nozzle and/or not a new burner head. There are 3 firing rates for the V7. They called the kits mid or high efficiency. With the indirect I would not drop th the high efficiency but the mid-efficiency was just a nozzle change. I would have to wait till monday to get the recommended nozzle size for the mif-efficiency. I believe it was one size smaller but not sure.
 
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Old 10-25-08, 01:39 PM
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If you could get me the info that would b e great, thanks!

I changed the expansion tank for the cold water supply to my indirect this morning. I bought a gauge to check my house pressure so I can match the pressure in the new tank, and to my horror I got a reading of 130 psi. My PRV was toast. I have no idea how long ago it failed. I'm guessing not too long ago or something probably would have failed, but who knows.

I thought that was really high, but he guy at the plumbing supply house around the corner wasn't surprised by that reading. He said my town is notorious for high water psi.
 
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Old 10-25-08, 03:30 PM
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No... I don't believe that's NORMAL for any city water system... where did you install the gauge ? On a hose fitting outdoors ? or on the drain of the water heater ?

Reset the high pointer, run the hose for a few minutes, and put the gauge back on... I bet it's not over 80 ... if it still reads 130, I would strongly urge you to get in touch with your city water people and ask them WTH is going on over there ? and if they say that's what they run at, then have a plumber install a pressure reducing valve in the main line from the street. (and send the city the bill!)

I think what you were seeing is the result of your expansion tank not being functional. That's it's purpose, to keep those spikes down. If you have a tank on the water heater, you probably have a check valve in the line feeding the heater. If the expansion tank has failed, you could EASILY see 130 PSI on the hot side ...
 
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Old 10-25-08, 05:03 PM
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Trooper, I assure you that 130 psi is not abnormal for many city water systems. I'll agree that it is in the best interests of the homeowner to install (or have installed) a PRV to bring down that high pressure.

Here's a picture I shot last spring of a city water pressure gauge. I assure you that there are at least 100 homes in the immediate vicinity of the location of this gauge and I'll bet money that few of them have a PRV in their water systems. Nor is this an isolated instance in Seattle. I could probably point out thousands of homes in Seattle that have water pressure over 100 psi and no PRV in the house.

I can also guarantee that if any homeowner sent a bill to the city for installing a PRV the city would deny the claim and the office workers would get quite a laugh besides.


But all that aside, pkovo is under the impression that the expansion tank for his heating system should have the same precharge pressure as his domestic water supply. I know that you know better but we must tell pkovo that his impression is absolutely WRONG; the heating system expansion has to have the precharge pressure of the HEATING system cold PRV setting, about 12 to 15 psi.
 
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Old 10-25-08, 05:29 PM
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I believe I removed the possibility of thermal expansion from the tank effecting the reading, but it made no difference. Actually, it changed by 2 psi, but that's it.

I put the gauge outside on a hose bib. Didn't believe it, so I tried another hose bib, same reading. At this point my indirect was already off for a few hours (preperation to change the expansion tank), water in the tank was probably down to 115 degrees or less. Regardless, I have a valve above and below the tank anyway. I blead some pressure out of the tank, and closed the valve above and below, effectively isolating it from the rest of my plumbing. I opened the hose and let it run for about a minute just to make sure any possible pressure was bled off. Checked again, and it was 128 instead of 130. Still ridiculously high.

I also checked with the gauge while water was running. I flushed the toilet and watched. While running, the pressure dropped down to 50 psi. Once the toilet stopped running, it went back up to 128. It didn't climb back up slowly either. Maybe it took a second. I was surprised it dropped to 50 though.

To clarify, the PRV valve I replaced IS on my main from the street. I already had one there, so I just replaced it. I have the new one set to 50 psi.

I thought that pressure was crazy too, but the guys at the supply house around the corner weren't at all surprised. They said my town and another town nearby are both real high. Something about our tower being extremely high. They said it actually fluctuates a lot and it's at it's worst when their pumping water into it, and in the evening when there's little draw??? One guy said some people in town had reported spikes of 170 over a holiday weekend (not sure how the holiday part factored into it). My town is hilly as well, not sure if that would factor in.

I did try to call the city water people, and no one answered. Small borough on a Saturday, I didn't really expect they would. I wanted to see if perhaps THEY were responsible for replacing a toasted PRV given the fact that the pressure is so high. I decided to just bite the bullet and do it myself since I had the time today.

Knowing my street pressure is that high makes me uneasy. My PRV is isolated with a shut off on either side. It has a union connection on one side, and a threaded adapter on the other. Makes it real easy to change. I suspect with my high pressure it's lifespan may be reduced, although it's rated for up to 300 psi working pressure. I may set up a gauge in a convenient spot where I can check it on a regular basis.
 
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Old 10-25-08, 05:34 PM
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I'm glad to know my town isn't alone in it's high pressure though.

I don't have the wrong impression, my thread just kind of migrated from my heater to my general plumbing. The expansion tank I installed for my heating system is precharged with 13 lbs to match my heating system. I installed that earlier this week. The one I installed today is a potable expansion tank on the cold water supply to my indirect tank. It is precharged to match the pressure of my water line. Which is now 50 psi.
 
 

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