Buderus g115 short cycle on one zone

bink · October 2015

Hello this is a new system and this weekend it was cold enough to test the heat zones. It appears the three zones work but the zone on the middle floor was cycling about 1 minute on and then shuts off does this repeatedly every 20 minutes or so. The baseboard barely Warms with this short run and I don't think the thermostat would react to so little heat to turn off the zone.
The outside temp was about 45 degree maintained about 70 degrees inside .wondering what could be causing this. I have the aqua stat control with three zones plus zone for water heater which has priority. I have one circulator before the zone valves.
Any help you can provide I will appreciate.
Thanks
Rich

Bob Bona_4 · October 2015

It sounds like a valve is off or the heat loops are air bound and the boiler is bouncing off of high limit. Did you install?

bink · October 2015

The installation was done by a heating contractor. I tried them for the new system because my neighbor has been using them. A tech from this company will be here tomorrow to look at it.

bink · October 2015

To update anyone reading this the tech reset the hi low to 160-140 was at 150-140. He also replaced the old round Honeywell thermostat with a digital model 300. Hopefully between these two changes we should have less cycling. Outside temperature in eastern Pa. Is higher this week so it may be a few more weeks before I get to see for sure.

Robert O'Brien · October 2015

Low setting? Low should be off on G115

bink · October 2015

Thanks for the posts. The /4 was installed. The contractor used the total feet of baseboard in the house but no heat calculation based on size or insulation. I added insulation to the crawl space in the attic and other improvements better Windows and doors over the years so until the temp is 45 degree F or less there is not much heat needed. Probably complicated by the three zones.
My fault for not doing more research. I had a stainless liner installed this summer based on input I got on this forum so I guess the chimney will be ok with some short cycling.
I try to do things correctly but sometimes I miss.
Thanks for the help.
Also wondering what is the difference between the /3 and the /4 is heat output.
Rich

njtommy · October 2015

Is your zone getting hot now?
It sounded like you where having a zone problem when first reading the post. Not so much a boiler problem. I'm not too familiar with the G115, but a larger differential would increase your run time.

bink · October 2015

I am waiting for colder outside temperature. Because it warmed up we are not using the baseboard heat.
We had a few days of cold outside approx 45 degrees when I noticed the short run problem.. I also realized that the circulator may have been running without me noticing because the system is much quieter than my old system when circulating. So there may not be a zone problem.

the tech that came today felt that the hi low settings were too close together so he readjusted to 160 hi 140 low. Feels that is the problem.
I will post and update when we get colder weather. . I wonder what a normal run time should be? The boiler runs about 3- 4 minutes to heat the water heater tank after showers & washing machine. It was running 1 minute when the circulator ran the zone.
Thanks for reading my post.
Rich

Ironman · October 2015

How many square feet is your house?

Look at Robert's post. He's right: the low setting should be off.

In all probability, the 4 section is too big unless you have a large house. Unfortunately, you can NOT downfire a Buderus oil boiler, you can only upfire it.

You can probably reduce the short cycling by combining the micro zone with on of the larger ones. Other than that, and setting the control correctly, a buffer tank is the only other solution.

10 minutes minimum run time is what is recommended.

bink · October 2015

Ironman
Thanks again I still have lots to learn. how do you turn the low setting off and how does this change the operation. I agree that in retrospect the /4 is too big. Wondering what happens when running too short of a cycle .
. Condensation build up? Shorten life of boiler?
Rich

hot_rod · October 2015

The boiler should run long enough to warm above condensing temperatures, and long enough to warm and dry the entire flue passage and venting.

No doubt short cycles decreases the life expectancy, may cause corrosion, and leads to additional fuel consumption.

The goal of a buffer tank or high water content boiler is to provide long run cycles and long off cycles.

If you have small, or micro zones, adding a buffer may be the only workable fix.

If you go that route, there is some good reading and formulas in Idronics 17

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

bink · October 2015

Thanks hot rod
Interesting site. Not sure I would do this but I can see the advantages.

bink · October 2015

I tried a few settings changes. But what I notice is that the problem of the real short cycle only occurs with a request from the zone baseboard. Turning the low off worked good except when the zone for the house starts the that circulator. After the.circulator ran about a minute the boiler turned on at 140 and turned off at 142 degree. Less than a minute run time. This is the condition that has me concerned.
Anybody have any thoughts. What is different on the Hydrostat control between running the independent water heater and the other zone valves?
Thanks for reading/ helping

bink · October 2015

For anyone still following this post I found that part of the problem with the very short cycle less than 1 minute boiler run was that the economy dial was set to 5 zones. According the tech at hydro level the economy dial should be turned off if the low limit it set. Even so with low off I saw the 2 degree differential shutdown the boiler yesterday 1 minute
So I turned the economy off and set the low to 140 degree for now until I can discuss with heating contractor. I may experiment with the low turned off as suggested by Robert with a lower economy setting.
Still trying to learn hopefully.

Buderus g115 short cycle on one zone

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