Boiler cycling in 1-minute intervals, heat generally working terribly

arctic_colors

Hi — I bought a house with a heating system that I knew had some issues, but it is clearly not cut out for this polar vortex. Here in NJ it was 7º last night, and the house got as low as 59º even with the heat running constantly since the night before (thermostats all set above 70). Currently it is 17º out and the thermostats (still set over 70º) say it's 62º in the house.

The boiler cycles on and off at a rate of roughly 1 minute on, 2 minutes off. Looking at the boiler's control panel, the "LIMIT" light comes on when the water temp drops below 160º, then the boiler ignites and runs it hits 180º, generally between 45 and 75 seconds later. Then the water temp drops over the next ~2 minutes before the cycle restarts.

There's 1 circulator and 3 zone valves — all 3 zones are calling for heat and seem to be getting some. (House is around 2200 sq ft and there are two zones on the first floor and one on the second — partially finished 3rd floor/attic just has electric baseboard.) If I point an IR thermometer at an exposed spot on one baseboard radiator, the temperatures roughly follow this pattern (e.g. falling from 148º to 130º over about two minutes).

The boiler is from 2013 and seems to work fine. We want to put in a mod/con as part of an addition in a year or two. Is there anything we should check or can do (or rather, have a pro do) in the short term to improve the heating system's performance? Should I fiddle with the "boiler temp" and "economy adjust" knobs on the boiler? Is there a different pump we should have installed?

I've included a bunch of pictures of the boiler, pump, and piping — hoping the wealth of knowledge on this forum can point me in the right direction. Thanks for your help!!

mattmia2

Probably either air bound or the circulator isn't working. That boiler likely has decades of life left in it. Probably can use it for your addition depending on how it is sized to the current load.

fentonc

I'm located pretty near you (other side of the Hudson), have the exact same boiler and a similar 3-zone setup, and get pretty similar short-cycling behavior (mine usually fires for about 80 seconds every 6-7 minutes, but that's usually because only one zone is calling at any given time). It is possible that you have air in your system or something, but first let's check out what kind of baseboard you've got.

• How many linear feet of baseboard in each zone? Just measure the finned part for each zone and add it all up.
• Are the return pipes for all 3 zones getting to about the same temperature? (i.e. water really is flowing through all three zones)
• Are the bottom/top openings of the baseboard obscured by thick carpet, curtains, furniture, etc? Are the fins excessively clogged up with animal fur / dust / gunk?
• You can adjust the aquastat on the boiler upwards to 190-200. The heat output of baseboards is proportional to the temperature difference between the fins and the room air temp, so the a higher aquastat limit means the baseboards will put out more heat (and also result in longer burn times).

fentonc

I did a big write-up / analysis of the behavior of my boiler a few years ago (before I started adding additional fun controls to it):
https://forum.heatinghelp.com/discussion/188257/end-of-season-report-hows-my-boiler-doing

hot_rod

without adding a buffer tank, I doubt you will “control away” a short cycling in a fixed output , multi zoned, boiler across a wide heating season temperatures.

If you crunched the numbers based on run time/ cycle efficiency that system may be in the 60- 70% range.

My main argument for modulating boilers, even on predominantly high temperature systems. You should run in the 85% range, properly sized and controlled.

Condensing operation on mild days, ODR controlled is icing on the cake.

ScottSecor

I am not convinced the following is one of your problems, but it might be a good place to start. Make certain your three thermostats are programmed/ set up for the the type of emitters you have. Looks like you have hot water baseboard. Make sure all three thermostats are set up correctly. If left at factory settings, they will likely be set for warm air heat, not hwbb.

Another thing I would recommend it to crank up the temperature of the boiler water temperature. In simple terms, 150 degrees gives off about half of the BTU's when compared to 180 degree water. Also, during this cold snap, I recommend lowering the economy setting. I like saving money on fuel too, but with an outdoor temp of seven degrees, this might not be the time to save a few pennies.

I also agree that your circulator may not be operating correctly. One way to confirm, is to start closing the ball valve above the pump and listen for a dramatic change in the piping near the circulator pump. Make sure to open the ball valve after the test.

arctic_colors

Thanks everyone!

I vacuumed out some of the dust/fur/stray plaster from most of the radiators and turned the water temp up to 200º — now the boiler cycles on/off between about 170º and 200º instead of 160º to 180º, and it seems like the house is staying at least 5-6º warmer, even with windows cracked upstairs to air out paint fumes.

So it sounds like I at least want to get someone out here to try to bleed air out of the system if there is any (and maybe inspect the air separator valve?), and to inspect/possibly replace the circulator. Would love to learn to do this myself but dead of winter with freezing temps probably isn't the best time to dabble with the heating system…

It also looks like the boiler's installation manual calls for balancing valves on each zone, which I don't seem to have, and says "the fill valve must always be connected to the expansion tank", but it looks like my fill valve is before the circulator and the expansion tank & air separator are between the boiler and the zone valves. What difference might this make to the system?

@ScottSecor I tried the close-the-ball-valve test, but wasn't sure what to make of it — I think it sounded minorly different, not dramatically different. The pump does feel like it's doing something (vibrating slightly if I touch it). I did previously configure the smart thermostats (two Ecobees) to know that I have a boiler, although I assumed the only difference this makes is that they don't turn on the air handlers when calling for heat.

@hot_rod since I expect to put in a modulating boiler in a year or two, presumably a buffer tank doesn't make sense to really think about now — just get everything designed properly if/when we put on an addition? The short cycling is weird to me but not a big deal in the scheme of things, I just want the house to stay warmer.

@fentonc do you have any details on how you built/set up your "boilertron"? Sounds like an interesting project

hot_rod

if cranking up the temperature solved the lack of heat issues , it could be the amount of radiation is a bit low.

Is it fin tube? How many feet total?

I would guesstimate that home to have a heat load in the 50- 60,000 btu/hr range, based on a 25 btu/ sq ft number

The boiler you have is a 140,000 so possibly twice the size you need.

If my guesstimate is close at 60,000 you would need about 120’ of fin tube at a 500 btu/ ft output

Evenly split that 60k would be 20 K per zone,when only one zone calls the boiler is 6 times too big.
If one zone is small, maybe a master bedroom zone, things are getting worse. That is where the one minute run time might rear its head. Also driving the run cycle / cycle efficiency number into the ditch.