hot water boiler short firing


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Old 01-18-10, 02:16 PM
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hot water boiler short firing

I noticed recently that my boiler turns on and off quickly. It will run anywhere from 10 seconds to 1 minute. I had a professional come out and look at the boiler and of course the problem did not occur while he was onsite.

He said my thermostats were the culprit. He stated the zone valves (I have three) are slow to open, and by the time the zone valve open up and water flows into the boiler, the thermostat had already stopped calling for heat.

When this situation does occur, I noticed the temperature gauge on the boiler does not reach 190 degrees when the boiler shuts off.

I have two digital thermostats and one analog (mercury). He said the differential should be increased on the digital thermostats to a few more degrees. I looked through the manual of both, and they do not have this option. I have a three year old Honeywell RTH7500D and a Rite-Temp digital thermostat. Not sure how old the analog thermostat is.

The professional that came out showed me how to determine what zone was calling for heat by checking the tension in the zone valve lever. I haven't been able to sit around and check if all of the zone valves are opening each time the boiler turns on and off quickly. Besides, I am not even sure if I would be able to figure out what the issue is by determining if the valve was open or closed when the boiler turns on and off so quickly - especially if the valves are slow to open and close.

I was told the boiler should not operate in this fashion. Any help in getting to the bottom of this issue would be greatly appreciated.

Or, is this normal? If it is not, how worried should I be? Is it harming the boiler?

One final note, my heat is working fine. I noticed this issue when I started spending a little more time in the basement and kept hearing the boiler turn and off frequently.

I appreciate any insight!
 
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Old 01-18-10, 02:20 PM
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There are normally menus in the electronic thermostats that allows you to choose the right application.
Your boiler may be controlled to maintain temperature. Does this happen all the time? Does your boiler make hot water?
 
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Old 01-18-10, 05:07 PM
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I ain't buying the 'satisfied thermostat' line at all...

This is something that just started happening, right? You've lived in the home for long enough to know how the system USED to run, right?

And why would the thermostat sastify ten seconds after it called?

rbeck asked a few good questions, and one in particular... does your boiler provide domestic hot water? or do you have a separate water heater?

I think the best advice at this point is to observe the system and see if you can determine a pattern... like " It happens every time _____________________ " ...

Besides, I am not even sure if I would be able to figure out what the issue is by determining if the valve was open or closed when the boiler turns on and off so quickly - especially if the valves are slow to open and close.
But you might! Here's a few pointers... if a valve is OPEN, the CIRCULATOR PUMP should be running. Have you noticed if it's only the burner that is cycling, and the pump continues to run? This is important, because there ARE times when the water temperature will high the high limit of 180-190 and the burner will shut off, but the pump will still be running. In general, if a thermostat is calling for heat, ANY thermostat, the pump should be running... (with possible exceptions, if your boiler provides domestic hot water)...

The burner MAY turn off before it hits 190 water temp... if the thermostat satisfies...

Keep watching, as I said, look for observable 'patterns'...

OH, and tell us what make/model boiler you have, and what fuel you burn!
 
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Old 01-18-10, 06:58 PM
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more info and update

Thank you for the input. When I came home tonight I caught it turning on and off very quickly - the water temperature was cold, according to the gauge on the front. I checked all the zone valves, they were all closed. I noticed the pump was on while the boiler was firing. Also another note, I noticed the all three feeds are not warm or hot, certainty not indicative of the system running and needing to reheat circulating water that fell below the designated temperature. I will keep a closer eye on the system tonight to see if there is an pattern. I guess part of the issue I am struggling with is how do I know if a zone is legitimately calling for heat, or if the boiler is acting funny when it is turning on and off quickly?

I've lived in the home for a while, and just recently noticed it, as I've been in the basement more often this season. I do know that most often it will run for longer periods of time, when a zone is calling for a heat during a major temperature adjustment. Two zones are baseboard, and the third is cast-iron radiators.

As for more information, my boiler is a Weil McLain CGa-5 natural gas fired unit. It does not provide hot water for the house.

Regarding the thermostats, the first digital thermostat has a setting for the heating system type, which is configured correctly. While the second digital thermostat only allows you to set swing temperature for the difference in the room to the desired temperature. This is set to 3 degrees.

Thank you very much.
 

Last edited by jdubs; 01-18-10 at 07:36 PM.
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Old 01-18-10, 07:28 PM
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one more note

One additional note, as I was babysitting the boiler I forced open one of the zone valves, and the the boiler started up shortly thereafter. Upon closing it manually, it shutdown immediately. I tried this again on another zone, but the boiler did not start up.

Also, during one of the short cycles, I was able to check one of the thermostats - it was not calling for heat. It was the thermostat tied to the zone mentioned above, that when opened manually, the boiler fires up.

One thought, I have the thermostat temperature down very low (60 degrees), whereas the boiler is not running often - I noticed the water temperature stays around 75 degrees, and will rise up to 80 or 90 degrees during the short firings.

Is there a minimal water temperature setting on the boiler? If so, I am wondering if this would cause the short firing?
 
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Old 02-09-10, 08:22 AM
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Hi
i have just removed my old room thermostat, and replaced it with a drayton digistat+3, and i noticed that when the stat is'nt calling for heat the boiler fires for a short while, then goes out, thet stat seems to work ok, ie when it calls for heat the pump, and boiler all operate at once, i dont know if this happened when the old stat was in place, as i had no need to check, maybe it did, i now leave the boiler in the always on mode, and let the programmable stat do its bussiness, and ive noticed at cetrtain times, the boiler fires then stops, so maybe this is normal
 
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Old 02-09-10, 10:52 AM
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jdubs, what do you have for zone valves. If they are taco it is imperative that the t-stat be set at .9amps to properly operate them. All zone valves should match t-stat but with taco it's very important. If you don't have the right amps it's like a brown out for the valve. It reacts the same way a light blub would be on 80 volts. What happens with the valves is it wants to open and sometimes it does and sometimes it bounces on and off. That on and off is your boiler short cycling. Taco came out with another zone valve that ran on a lot less amps but I haven't heard much about it. Don't know if that's your problem, might be worth a mention. Another point about taco is besides the poor performance, they will burn out rather quickly sometimes without the right amps. I could make a good living changing them because of the wrong settings. I installed 7 of them in my own house back in 1984 and have only repaced 1 due to failure.
 
 

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