New Gas Boiler "short cycling"

Ismellelephant · March 21

I had a new Weil McLain Cgi PIN 4 gas boiler installed and it appears to be "short cycling". After 3 or 4 visits from the installer they are now claiming this is normal. Recently in 20 degree weather the house only reached 67 degrees despite the thermostat being set to 70 degrees, and all through the night the boiler would shut off and on every 1 to 2 minutes.
Shouldn't this boiler run constantly until the set thermostat temperature is reached?
Purging the air in the baseboard system and a thermostat replacement didn't solve the short cycling. Thanks for any info.

neilc · March 21

did you get air?

is the circ running?

post some general pictures,

system pressure, and temp at boiler?

pecmsg · March 21

Is there a 1st and 2nd floor?

kcopp · March 21

Running and firing are 2 different things. Sounds like the boiler is firing but will only give up some heat and not satisfy the zone.

Could be air. Could be improper circulator/ flow.

Ismellelephant · March 21

Thanks for the replies.

There is no air in the system, a purge was done.

It is a one floor ranch house, one zone and about a 1000 sq ft house.

Running and firing, when the boiler reaches 160 degrees, it fires up, in about a minute or two it reaches 180 and fires off. The circulator is very quiet but I believe it continues to circulate when the firing is in its off cycle. It just continues this over and over again.

In 40 degree weather the house will reach set temp even with the 1-2 minute cycling, but in 20 degree weather it fails to reach set temp.

I understand the firing off and on to satisfy the 160 to 180 deferential. But when there is a call for heat shouldn't the boiler continue to fire until the thermostat set temperature is reached instead of firing off and on?

This is the system pressure meter

Jamie Hall · March 21

At first impression, either there is still air — in the boiler circuit — or the boiler pump isn't circulating throug the boiler.

neilc · March 21

can we get a wider shot of the boiler/

floor to ceiling, showing circ, expansion tank, all in one, maybe from a couple angles

Ismellelephant · March 21

I am not at the home right now but will post pics.

I do know everything was replaced, water regulator, backflow valve, new vents, new circulator, expansion tank. I also asked the installers if the boiler might be oversized and they said it is not.

Maybe this isn't a yes or no question, but when there is a call for heat shouldn't the boiler continue to fire until the thermostat set temperature is reached? The boiler replaced "seemed" to operate this way and would run for 10 minutes or so till thermostat temp was reached.

neilc · March 21

the boiler is hitting the high limit at 180(adj), and shutting the burner down as it should, you're not getting the boiler heat into the house,

it doesn't sound like you have proper circulation, or there's a bypass, or ??

did the old heat work to setpoint before the new boiler?

pecmsg · March 21

water temp in and out of the boiler?

Ismellelephant · March 21

I know of no bypass and when in the 40's it will reach thermostat temp. I have no info to offer on the old boiler other than is would run for 10 minutes or so when heat was called for.

So if the boiler is hitting the high limit at 180 and shuts the burner down is how it should work, then at this point I'll probably have to wait until we are in the 20's again and see what happens.

I really appreciate all the info.

hot_rod · March 21

Could be the boiler is oversized. How many feet of fin tube is connected?

CGi 4 is about 88,000 output

Typical fin tube is about 500 btu/ft. So you would need about 176' of fin tube to match the boiler

a WAG for 1000 sq ft of home would be under 30,000 btu/hr needed. A load calc would tell a better story.

But the boiler could be 3 times the size required?

So on the coldest day it will short cycle on milder days the cycling will be even shorter.

kcopp · March 21

Simple question…. Is all the piping hot? Supply out to the system and return?

Go out 10 feet from the boiler… still hot ?

The other possibility here is that the old boiler ran VERY hot (200F) and the new one runs at a more conventional temperature…hence the reason it cant "keep up"

The system may need more baseboard because it is under radiated.

109A_5 · March 21

If the old boiler worked as you would expect, not short cycling, and heating the home as expected. And the new one is short cycling and NOT heating the home as expected. The question is what significantly changed. Assuming the new boiler is not significantly oversized.

It appears system presently can't move the boiler's heated water throughout the house correctly, to heat the house appropriately, trapped air, circulator issues, bypass not set correctly or some restriction in the piping can cause this situation.

Since the boiler is not heating the house correctly the boiler's water heats up too quickly reaching the high limit 180 degrees and that shuts the boiler's burner off. It is normal for the boiler's burner to shut off if the boiler's water temperature gets to 180 degrees.

The question is what significantly changed.

Additionally if it was just an oversized boiler situation the home would probably heat fine (or at least as well as it did before) even though it may short cycle.

hot_rod · March 22

Do you recall what size the old boiler was, btu/hr input?

Ideally you want to see a 10 minute run time every time the boiler fires. Frequent short cycles will drive the boiler efficiency down also.

Even without a cold day you could crank up the thermostats and get some readings on temperature supply, and temperature return at the boiler.

That gives you an idea of adequate flow.

Clamp on thermometers or even a point and shoot temperature gun would work. Klein is a good brand.

Ismellelephant · March 22

hot_rod
I am not at the house right now but I doubt there is even 100' of fin tube. Maybe 80'?
I will measure when I am at the house.

kcopp
Yes the piping is hot at the baseboards and at the out and return to system.

kcopp
Hard to say if the older boiler worked any better. This house is in a vacation area mainly used by the family in warmer weather. Only since I retired has the house seen use in the winter and I noticed the issue.
The older boiler was a Weil McLain Gold Series CGi-4-PIN about the same BTU rating.

I am beginning to think oversized could be the issue. The installers just replaced the old boiler with a similar size boiler and no load calculations were done to my knowledge.

hot_rod · March 22

60-70’ of 3/4 fin tube is a typical loop design, max. length

70 x 500 would require a boiler with a 35,000 btu/ hr output. So a small 45- 50,000 btu/ hr sounds about right for a 1000 sq ft home.

If in fact you have the CGi-4 it is substantially oversized. Unless you have a Series 4 which comes in various sizes. A Series 4 CGi 25 feels like a better size, 41,000 output

An 77,000 output boiler like I think you have would like 7 gpm flow to move the heat out

3/4 fin tube is typically pumped at a. 1-4 gpm flow.

So that could be the cause of the short cycles, you cannot move the heat output of the boiler fast enough.

If it is piped and the same size as the previous boiler it should heat adequately, even with the rapid in/ off cycles.

Perhaps there is a plugged strainer or air sep, a valve not fully opened?

neilc · March 22

any chance you got new carpet also, or furnitures, and you're blocking airflow to the fintube?

Ismellelephant · March 23

hot_rod
I am not sure what a plugged strainer is, but I will check if a valve is not open.
I hope to be at the house Thursday and will take pictures and measure the total length of the baseboard fins.
Thinking ahead, if more baseboard fins are needed, that may be the most cost effective solution over yanking out the new boiler and replacing?

neilc
No nothing has changed in the house. This house has done vacation rentals in the pass with vacationers with cats and dogs.
I plan on cleaning the baseboard fins, I am sure they are in need of cleaning.

4GenPlumber · March 23

Vacation home that didnt see people in the winter? Sounds like an insulation problem, not the size of the boiler. The boiler firing on and off are a function of the aquastat, thats its job. If the problem is the house isnt getting to the temp to satisfy the thermostat, that was never set that high during cold months before, it sounds like the house (like many vacation homes) isnt insulated properly.

JUGHNE · March 23

These symptoms have been reported here over the years after a boiler change.

And sometimes it is the pump has been installed backwards.

Pictures of the install and showing the pump would help.

I have seen it here about 6 times.

tcassano87 · March 23

definitely need pictures of the install for anyone to give the best opinion on the issue.

Do you know if you have a maniflow tee system by chance?

Ismellelephant · March 25

4GenPlumber

About the insulation, the house has been lived in full time in the pass. There is R13 in walls and two layers of R13 in the attic.

I am going to be at the house tomorrow, I'll measure how much baseboard and take pictures of the install.

I really appreciate the help, you've guys have been great.

Ismellelephant · March 28

I measured the baseboard fins, there is a total of 57 feet. I wasn't sure of the location where to measure the Send and Return temperature.

This is a diagram of how the boiler is plumbed.

more pics

Jamie Hall · March 28

AAgh. Expansion tank in the wrong place, but we'll let that go.

Measure your feed temperature just after the expansion tank. Measure the return temperature just before the circulator pump.

EBEBRATT-Ed · March 28

Expansion tank can't be on one side of the circ with the water MU on the other side of the circ.

The boiler is way oversized. Don't know if the high limit has an adjustable diff (probably not) but I would add another control to reduce the short cycling. Run it to 190 and let it drop to 140 to reduce the cycling

Ismellelephant · March 29

I measured the temp just after the expansion tank and just before the circulator and the results don't make sense to me. I tried two different temp readers.

I do believe on the old boiler the expansion tank was located in line with the water suppy. Would the expansion tanks current location cause short cycling or heating issues?

Would adding more baseboard fins be a solution?

Jamie Hall · March 29

If those num bers are anything like correct you are getting very little if any circulation. All valves open? Is the circulator pump even running?

Ismellelephant · March 29

I see no closed valves and the pump is so quiet I can't tell if it is running or not. Any tricks to determine if pump is running? I could disconnect the power to the pump and see if I can detect a difference in heat at the baseboards?

neilc · March 29

do you have a meter and know how to use it?

you could amp the circ, and confirm voltage going to circ,

if no power going to circ, temp an extension cord to circ,

those temps on your last screenshot suggest no circ as Jamie said,

any chance you're air bound?

kcopp · March 29

That is a Taco 007e… What color is the light on the front?

Ismellelephant · March 29

https://forum.heatinghelp.com/discussion/comment/1893191#Comment_1893191

Yes I can check voltage going to circulator. I also have a clamp on meter for measuring AC current which might be useful but not here with me now. Air has been purged by the installers on the second to last visit.

Ismellelephant · March 29

https://forum.heatinghelp.com/discussion/comment/1893192#Comment_1893192

Color light on the front of what? I see no lights on circulator.

109A_5 · March 29

What temperatures are at the Orange arrows ?

neilc · March 30

https://forum.heatinghelp.com/discussion/comment/1893199#Comment_1893199

no lights, no power (120v) ,

neilc · March 30

there should be a lit LED on the flat end of the circ motor, red, or yellow, or flashing, if power is being sent to the circ,

post a picture of the other end of the circ bx cable where it enters its control, with the cover off the control, so we see the connections inside,

also post a general wide angle shot of the boiler, circ, ex tank, everything, floor to ceiling, so we see a complete veiw,

pedmec · March 30

is the circulator wired to the boiler control?

what do the lights indicate on the boiler control?

Can you take a pic of the boiler control?

109A_5 · March 30

If the circulator is not working the boiler maybe sort cycling on the High Temperature Limit and you are just getting gravity heat.

I assume the Power and TSTAT/CIRC status is active.

Ismellelephant · March 30

I confirmed the circulator is running. Light is Amber when running. It continues to run when the boiler isn't at flame.

Took temp readings again.

The boiler is in a crawl space so tough to get wide pictures.

Circulator Wiring

Control Panel

pedmec · March 30

You either have air in the circulator or you impeller is broken off and the motor is free wheeling. You need to purge the circulator at the drawoff on the return going into the boiler after the circulator with the supply ball valve closed. The circulator has a check in it so you can't back purge it thru the supply. And the return purge is before the circulator so that won't work. This will force the system water thru the circulator. And make sure your purging with the circulator off.

neilc · March 30

in your front picture, what's the black round thing on top of the boiler, looks like copper is piped to?

That's not another circ, is it?

can we get a better picture of that

New Gas Boiler "short cycling"

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