Boiler goes on and off every 5 minutes


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Old 11-12-07, 10:45 AM
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Boiler goes on and off every 5 minutes

We've had some boiler issues for awhile now. We have oil heat, baseboards in house. First we we're getting hardly any heat, and figured out that the boiler was hooked up wrong. We fixed that and we are getting more heat, but not as much as I think we should be getting.

I've also started timing the boiler and it comes on for 5 minutes and then shuts off for 5 minutes, 24 hours a day. Is that right? Seems like just when we're starting to get some heat it shuts off.

We had a plumber in here for another problem that told us he thought it could be the pipes running from the boiler - they are only 3/4 inch and he said they should be 1 1/4. Their quote to fix the pipes was $2,200. Very confused and frustrated, and don't want to keep throwing money at things "hoping" they are the problem.

Any thoughts or advice?
 
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Old 11-12-07, 11:01 AM
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I'm not sure what your understanding of your heating system is but here's a simple analogy.

Your house is a leaky bucket - it leaks heat. The boiler converts fuel into heat (factory) and the pipes distribute the heat (like a railroad).

The t-stat tells the boiler when to make heat, and the aquastat tells the boiler when the distribution system is full of heat so that the factory can shut down for a while so that the distribution system doesn't get overloaded. A typical aquastat might shut the boiler down at 180F and then start it back up at 160F if the t-stat is still calling for more heat. Even though the boiler is shut down for some of this the pipes are still adding heat to replace what is lost.

If the pipes can't carry away much heat, then the boiler can't keep running for very long because the water gets up to its maximum temp.

3/4" pipe can move about 40,000 BTUs an hour and 1-1/4" pipe can move about 140,000 BTUs an hour.

What size is the house?
What size is the boiler?
Has the house always had heating problems?
What type of radiators do you have?
Is there more than one zone?
 
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Old 11-12-07, 11:39 AM
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I'm not sure what your understanding of your heating system is but here's a simple analogy.

Not boiler savvy AT ALL

What size is the house?

2300 sq feet

What size is the boiler?

Not sure, but will go look

Has the house always had heating problems?

Yes, we've had heat issues since we moved here 2 years ago.

What type of radiators do you have?

baseboard

Is there more than one zone?

3 zones, the house is V shaped, guestrooms on one side, master suite on the other, and one big open room for living area, dining and kitchen in the middle. The middle area is the one we have problems keeping warm. The other two zones we hardly turn on (the master bed we really only turn on at night, and the other 2 bedrooms only occasionally)
 
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Old 11-12-07, 11:58 AM
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[QUOTE][I've also started timing the boiler and it comes on for 5 minutes and then shuts off for 5 minutes, 24 hours a day. Is that right? Seems like just when we're starting to get some heat it shuts off.
/QUOTE]
First have to ask how is the boiler set up to run .What controls the burner?Control on the boiler set for heat??Or does the tstat turn it on or does the tstat turn the zone and pump on???
 
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Old 11-12-07, 02:42 PM
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Some more info from my husband, who knows a lot more about this than I do:

The Crown boiler is new and of good size for the house. The house has four zones one being the hot water heater, the other three rooms all controlled separately by their programable thermostat. We can turn it on or off with the thermostat if we wish. all of the pipes above the pump are 3/4 and 3/4 through the entire house. Problem is someone looked at the boiler and thought that below the pump and on the lower end of the boiler that the pipes should be larger. from 1 1/2 out going to 1 1/4 then to 1 then to 3/4 rather than 1 1/2 to 3/4 pipes and that perhaps the boiler was being choked and not flowing the water through efficiently enough. Further more our boiler is set to shut off at 190 and start at 160. The thing is the boiler turns on at 160 for exactly 5 minutes which is when it reaches 190 then shuts off for 5 minutes regardless of if it reaches the desired room temp. So basically it cycles on and off every 5 minutes. The though of the larger pipes was that while it IS on it might generate more heat through the radiators that right now barely "leak" heat rather than crank it out as I've experience before.
 
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Old 11-12-07, 02:57 PM
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Originally Posted by pamilli View Post
The Crown boiler is new and of good size for the house. The house has four zones one being the hot water heater, the other three rooms all controlled separately by their programable thermostat. We can turn it on or off with the thermostat if we wish. all of the pipes above the pump are 3/4 and 3/4 through the entire house. Problem is someone looked at the boiler and thought that below the pump and on the lower end of the boiler that the pipes should be larger. from 1 1/2 out going to 1 1/4 then to 1 then to 3/4 rather than 1 1/2 to 3/4 pipes and that perhaps the boiler was being choked and not flowing the water through efficiently enough. Further more our boiler is set to shut off at 190 and start at 160. The thing is the boiler turns on at 160 for exactly 5 minutes which is when it reaches 190 then shuts off for 5 minutes regardless of if it reaches the desired room temp. So basically it cycles on and off every 5 minutes. The though of the larger pipes was that while it IS on it might generate more heat through the radiators that right now barely "leak" heat rather than crank it out as I've experience before.
Was the boiler properly sized to the heat load of the house? What is the size of the boiler, and what is the calculated heat loss for the home? Some cycling is normal on days when the outdoor temps are well above the design temp. for the system.

Is the near in piping on the boiler at least 1-1/4"? With 3 heating zones you may only need 3/4" pipe for each individual zone?? Without knowing the amount of radiation, and heat load, for each zone the size of the piping would be pure speculation as to whether it is large enough or not for the heat load.

How about some photos of the near boiler piping and the pump, zone valves, etc. to show the piping. Did you ask the installer why it is cycling? It sounds like the plumber is making wild (expensive) stabs in the dark at the root cause of the problem; unless he has some concrete figures and data to back up the claims. That means a heat loss study and measuring the radiation at a minimum.
 
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Old 11-12-07, 04:25 PM
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Originally Posted by pamilli View Post
So basically it cycles on and off every 5 minutes. The though of the larger pipes was that while it IS on it might generate more heat through the radiators that right now barely "leak" heat rather than crank it out as I've experience before.
160-190* water and the baseboards aren't HOT ? No, something else is wrong... are you sure the circulators are running ? and/or the zone valves opening ?

And it STILL cycles like that every 5 minutes even AFTER the rooms are warm and the thermostats are satisified ? in other words, if you turned all the t'stats down to say 50, the boiler is still cycling ?

Yes, pictures please...
 
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Old 11-12-07, 04:36 PM
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Originally Posted by NJ Trooper View Post
160-190* water and the baseboards aren't HOT ? No, something else is wrong... are you sure the circulators are running ? and/or the zone valves opening ?

And it STILL cycles like that every 5 minutes even AFTER the rooms are warm and the thermostats are satisified ? in other words, if you turned all the t'stats down to say 50, the boiler is still cycling ?

Yes, pictures please...

Opps! Missed that part! Was is the pressure showing on the boiler gage? How many floors are being heated in the home? No heat being delivered would definitely cause short cycling!!!

Pete
 
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Old 11-12-07, 05:26 PM
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sounds to me that you don't have enough radiation to heat the area or the boiler isn't large enough. If the demand is such that the boiler never stops running it sounds like the room never gets to temp

what size boiler and how many feet of baseboard in the great room and how far is the boiler away from the room?
 
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Old 11-12-07, 07:59 PM
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Cycling

I've been working on a similar problem. In my case, the boiler is too big for the house & it's a monoflow tee system we've yet to get all of the air out of.
Cured one problem of one zone overheating. System was wired in such a way as to bring on both circulators when the primary zone called for heat. Installed a separate zone relay.
 
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Old 11-13-07, 05:51 AM
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That baseboards do get warm, but I definitely would not describe them as hot.

No, the boiler would not be cycling if the t'stats were turned down to 50, it just pretty much works all day/night in the winter time to achieve and sustain a normal temp in the house.

The boiler size is a 120,000 BTU.

Our house is on one floor, the boiler is directly under the great room in the small unfinished basement area. There are about 26 feet of baseboards in the room.

Sending pics shortly guys!
 
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Old 11-13-07, 08:24 AM
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I have one small zone with around 30 feet of fin tube that is feed with 3/4" tubing. Getting heat to that zone was never an issue! I doubt the piping to your zone is the issue.

Did the system ever work? This could be caused by a worn circulator too. Kind of hard to guess what the cause is.
 
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Old 11-13-07, 02:45 PM
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Originally Posted by pamilli View Post
We had a plumber in here for another problem that told us he thought it could be the pipes running from the boiler - they are only 3/4 inch and he said they should be 1 1/4. Their quote to fix the pipes was $2,200. Very confused and frustrated, and don't want to keep throwing money at things "hoping" they are the problem.

Any thoughts or advice?
As mentioned in some other post yesterday?, I work on this rental that has a prehistoric boiler in a crawl space cellar that supply finned 3/4 copper baseboards throughout house level. It is all in series; one continous run!!

It comes up from cellar, It goes length of bed. #1, into a hall closet, continuing under length of bathtub, across long length of bathroom under entry door, across kitchen, around great big huge L.R. that has bay window protrusion and goes around all of that, then continues across a big bedroom wall, down the adjacent bedroom wall, and into a bedroom closet, where the completed supply line then returns to the boiler, to do it all over again. Scores and scores of feet of run!

The end of that supply line is almost as hot as it is at the source!

Show THIS post to your plumber!
 
 

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