I would like to get a better understanding of what a normal boiler cycling period (time between firing) is when there is no demand on the system. My boiler is cycling every 15 minutes for 3 to 4 minutes when there doesn’t appear to be a demand. I have observed this in the summer when all thermistates are off and no hot water is being used (system heats a well insulated hot water tank). This is consistent during the winter during periods when there doesn’t appear to be a demand.
System set up.
– 130,000 BTU Quietside boiler – three years old
– Heatlink controls
– in slab hydronic heating
– boiler heats hot water tank
This is not a trouble shooting exercise, but would rather input from a HVAC professional if this cycle period sounds off. If so, I will hire a local contractor to figure out the details.
Thank you for your input in advance.
Mark
Edited 10/31/2009 11:19 pm ET by Mark Henry
Replies
First, I'm not an HVAC professional but deal w/ systems all the time. I'm inclined to agree that it sounds like it is cycling too much. Maybe you have a 'leak' (i.e. an uninsulated piece of pipe). Do you have a pump between the boiler and the storage tank? What controls that pump? I assume the boiler is well insulated. I also assume the piping is also insulated.
the pipes are partially insulated. it is on the to do list to finish the job tomorrow. we will see if it makes a difference. the boiler is well insulated. not sure about the pump - there doesn't appear to be any controls.
Even if the pump runs 24/7, it shouldn't cycle a lot, it seems. If the storage tank temp is satisfied, there is no reason for the boiler to come on. There is such a thing as a deadband or throttling range ... the temp range that the controls say I'm satisfied vs. I need heat. That may be typically 4 Fdeg ... i.e. let's say the storage tank is set at 120 degF ... the system comes on at say 116 degF and shuts off at 120 degF (or sometimes it will stradle the setpoint). All stats have this, but it tends to be transparent to most people.
Setting that aside, the run time bothers me too. If the throttling range was 'tight' causing frequent call for heating, the boiler may not run or run very little. Maybe some more details about the system. Not sure what 'heat link' controls are. Do you have a pump for the radiant floor AND a pump to heat the hot water tank? Floor pump is on a space thermostat, right?
Assuming you aren't overheating your floor somehow, the problem has to be on the domestic hot water side. Do you have a recirc. line in your domestic hot water system? If so and it's uninsulated, that could be the issue. That'd make 3 pumps.
Edited 11/1/2009 8:34 am ET by Clewless1
More details on the DHW system
The BoilerMate Classic Series (41g) tank is heated by two sources:
1. the water entering the tank from the main is heated by the boiler in what could have been a tankless DHW system, but the contractor found that it could not keep up with large demands such as filling a tub. this is the reason for the second heating source;
2. The tanks heating coil is supplied by the boiler in a closed loop. this line is spliced off the line that also provides space heating. This is where the DHW pump is located and by the looks of it is controlled by the tanks thermostat. These pipes are not insulated yet.
I can't distingues what the temp range is on this system. It is a vague digital display on the tank. will figure it out.Heatlink is brand name and is part of the systems controls connected to the thermostats. It is an injection control. This explanation exhausts my understanding. sorryThe house temp is comfortable so don't think it is over heating. The main zone valve is leaving at 100f.
"1. the water entering the tank from the main is heated by the boiler in what could have been a tankless DHW system, but the contractor found that it could not keep up with large demands such as filling a tub. this is the reason for the second heating source;
2. The tanks heating coil is supplied by the boiler in a closed loop. this line is spliced off the line that also provides space heating. This is where the DHW pump is located and by the looks of it is controlled by the tanks thermostat. These pipes are not insulated yet."First of all I know NOTHING about hydronic systems. But I have an engineering background. And while it is in electricity and nothing to do with this kind of stuff I an usually get some basic understanding of how a system works.And what you have makes absolutely no sense. The amtrol tank is designed to be the sole supplier of hot water. It is feed by domestic cold water supply and it has a coil in it that hot water boiler water is pumped through it when the water in the tank cools off. And unless they missed putting insualtion in the tank the Amtrol tank should maintain the hot water temp in the tank for HOURS without needing the boiler to run.But yours is also hooked up as though there was not tank. And the boiler has to run very often to maintain the boiler temp to keep that tankless coil at the desired temp.I THINK that whole system needs to be disabled. Might not have to remove the piping, but the controls need to be changed so that the boiler only runs when the tank (or the zones) need heat.If most of the hot water is used only during a few discrete time periods (early moringing, dinner, and late night) my guess is that wilt a proper setup, during the summer, the boiler will only operate during those time periods.http://www.amtrol.com/pdf/MC10009%20BMbrochure.pdfhttp://www.amtrol.com/pdf/SmartControl.pdfhttp://www.amtrol.com/pdf/9040-586%2001_09%20BoilerMate%20Indirect%20IO.pdf
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William the Geezer, the sequel to Billy the Kid - ShoeEdited 11/1/2009 3:47 pm by BillHartmann <!-- BILLHARTMANN -->
Edited 11/2/2009 11:23 am by BillHartmann
http://www.quietside.com/images/Quietside/Products/DPW/DPW%20Manual.pdfI don't know if this is the boiler that you have not not.Looking at the instructions I don't see any way to disable the domestic HW system. You can change the setpoint to the minimum.But, if I understand the operation correctly - and there is a 50% change that I don't, the boiler is set to maintain the space heating temp, except when domestic HW flow is detected and then it fires to the other setpoint.Might need to disconnect domestic water path through the boiler..
William the Geezer, the sequel to Billy the Kid - Shoe
While a hundred degrees may be adequate for floor heating, I'm thinking not high enough for your hot water or a hydronic basebd. Are you sure your boiler temp is set high enough.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
I will address some issues that have come up in previous posts.The 100F is running to the space heating zones. I am certain it is higher to the DHW tank, although still trying to decipher the set point display.The Quietside system highlighted in the previous post is not my boiler. I couldn't find my model on their website. It is 130,000 btu oil fired system. 2 years old.The pipes are fully insulated now, although don't think this is the primary issue. important anyway.Both DHW heating options can be easily turned off by closing valves. I will run two experiments to determine if turning them off separately will affect boiler cycle periods. I will turn off all space heating demand.Thank you for everyone's comments. This is a very useful discussion forum.
I figured out the DHW controller. The set point is 130F, with the differential set to 5F.
What is ideal for both settings?
The boiler is a Quietside QXM8-120F1-OL - see attached link
http://www.redbarnmg.com/Contents/Quietside/QXM8_Oil_Manual_1-13.pdf
http://www.redbarnmg.com/Contents/Quietside/QXM-OL_Specs.pdf
With these specifications someone maybe able to answer my original question which is what is a normal cycle period (length between firings)when there is no demand on the system (thermostats are turned off and no hot water is being used). Maybe the every 15 minute period is to be expected!
thanks for everyone's comments.
Edited 11/17/2009 11:42 pm ET by Mark Henry <!-- MARK_HENR2 -->
Edited 11/17/2009 11:44 pm ET by Mark Henry