3-min cycle on new boiler from cold. What's wrong?

aat879

I just switched from an old oil-fired boiler to a brand new 125,000 BTU Weil-Mclain gas boiler. I live in a two-story single-family house. The boiler was installed by a reputable steam company (highly recommended here), so I'm confident that the installation was done well. Drop header, new big beautiful main vents, the works. All the things that Mr. Holohan recommends.

Here's the issue:

I wanted to test the new boiler before the heating season sets in. With the boiler cold, I turned up the thermostat to call for heat. The burner came on and burned for about three minutes, then shut off. Puzzled, I went and cranked up the thermostat to 80 degrees (it reads high 60s), and the burner came on for about five minutes, then shut off. Then the boiler cycled on for about three minutes, then off for a minute or two, and repeat. Very gradually I could feel the riser/header/mains get hot, and a long while later some of the radiators got warm but not roaring hot as I would expect with the thermostat way up.

What's going on? Does this have to do with starting up the boiler from cold? I thought the boiler cycle was supposed to continue for a long time when the thermostat isn't satisfied.

Going to call the installation contractor soon, but I wanted to ask here first to see if there are any experts who can help me diagnose what's going on. It is extremely frustrating to have this happen after spending all that money for a new install.

Jamie Hall

It would help to know which of the two most likely controls is shutting it off: low water or high pressure. Without knowing that, it's a bit hard to say what might be pursued to correct the problem -- and the set of potential solutions is completely different.

So.. do you know what the pressure is doing as it fires? And, have you observed the water level as it's firing?

EdTheHeaterMan

Is the thermostat heat anticipator set correctly? We would need to know what thermostat you are employing for the system. Basically, between @Jamie Hall and @EdTheHeaterMan observations we are trying to determine what set of contacts is opening to cause the burner to stop? Is the thermostat opening and closing? Is the LWCO opening and closing? Is the Pressure control opening and closing?
so pictures of each of the controls close up with the cover off so we can see part numbers and from a little farther back would help.

JUGHNE

All of the above, also you may have a Cycleguard LWCO control which shuts down every 30? minutes for 90 seconds to study the water level. It would not short cycle as often as you have.

What does the sight glass look like as this on/off cycle happens?

EBEBRATT-Ed

@aat879

In addition to the above comments.

Is the boiler water level bobbing violently when running?

Did the contractor skim and clean the boiler waterside?

Did the contractor measure all the radiation when he sized the boiler? (even if oversized it should have run longer)

aat879

Thank you @Jamie Hall , @EdTheHeaterMan , @JUGHNE , and @EBEBRATT-Ed all for your help. I don't think it's low water or high pressure. The water is at halfway on the sight glass, and it does not surge at all when the boiler is firing. It does go down a little, as I expect it to do when some of the water is turned to steam, but then returns to the halfway point after the cycle as the condensate returns.

I suspect the issue is with the thermostat, and I'd like to focus there first on this troubleshoot. It's a old Honeywell T87 (I believe) with the simple dial. I removed the cover (the dial itself didn't want to come off, and I didn't want to yank on it), and a photo is attached showing the anticipator. From the little I've read, the setting seems too far to the right and is causing the boiler to cycle on and off, but I don't fully understand where it should be and don't want to mess with it without instructions. Would you kindly offer input on where I should set it?

While on the topic of tstats, two other questions. First, do you think it's worth it to switch to a digital or smart tstat? I don't really want to the programmability, which as I understand can be counterproductive with steam, but remote wifi monitoring and not dealing with the anticipator issue would be nice. Second, what does that TS-300 do (see second picture)? I was there when we bought the house, and I guess it's supposed to monitor remote temperature (outside?), but I can't really see the benefit in it. Can I safely get rid of it?

Thanks so much again for your help resolving this!

Jamie Hall

The T87 is close to bulletproof, and yours is set approximately correctly for steam. If the anticipator is set correctly (and as I say yours looks to be pretty close) it will do a better job of maintaining a nice even temperature in your house than any digital equivalent can, except some of the really expensive ones. Keep it.

I can see why folks are a little shy about anticipators -- most modern techs. have no clue how they work or are supposed to work, so .... "I don't understand this thing, throw it away" is their approach to adjustment.

That said, they can fail now and then (though usually not to create a short cycle)

But it is very easy to check whether it is the thermostat which is switching on and off. Simply turn the heat demand all the way up to say 85. That shouldn't cycle for quite some time...

JUGHNE

With that ring cover off you can see the action of the mercury bulb as it switches on and off.
The mercury in the glass bulb completes the circuit to the gas valve thru the small pins in the bulb.
So with the boiler in the short cycling mode you can watch the glass bulb, if it tips with the cycling that is the problem.

You can make it shut off by just breathing on the coil under the bulb, so don't get to close.

If it is short cycling because of heat anticipator, you can go for "longer" cycle time by moving the small brass triangle to the left. Use a ball point pen stuck in the triangle to move.

The heat anticipator is a small electric resister of wound wire, it as adjustable as you move the triangle to produce more or less heat.
It is energized when the boiler is on and heats the housing inside the tstat to prevent over shooting your room temp......you might say it "anticipates" the arrival of the boiler heat to the tstat.

I have seen shorted coils in tstats which would produce too much heat and short cycle the system, it can happen but seldom does.

Jamie Hall

I think that's a later T87 with the microswitch, @JUGHNE -- but your comments are still applicable. But I think it would have to a dickens of a short in the anticipator to produce a three minute cycle!

JUGHNE

My first experience with a steam boiler started with a shorted anticipator in an old HW Chromotherm? clock tstat.
110 year old church with 500,000+ btu boiler with constant on and off of burners, maybe the 3 minutes as above.
Very hot basement, pantry room next to boiler room so hot someone added an exhaust fan in the ceiling to blow air up into the boiler room.....but the only air to come into the pantry room was from the boiler room.
Well intended volunteers....

So new Visionpro programmable tstat, (church used maybe 5 days a week, 1 hour at a time), add main vents (now 10 G2's) where there were absolutely none, replace all rad air vents, (put faster vents to the front where most sat), there was one of each design from the last 100 years, including a hot water air vent. Re-pitch and support all piping. Insulate all piping. Now running at 8 ounces of pressure.

All of this pretty low hanging fruit that took the NG used/degree day from 1.48 down to 0.66 (looking at Jan and Feb months.....a feather in my hat, if I may say so myself.

This was 15 years ago and really sparked my interest in steam.

Thanks to Dan's books and the Wall, this has turned in a great hobby that actually pays.

mattmia2

Seeing the boiler controls could help, there could be some extra control that has a higher current draw than the standard controls that is making the anticipator setting too low.

EBEBRATT-Ed

@aat879

You can safely turn the anticipator toward longer it won't hurt to try as @JUGHNE mentioned.

aat879

Thanks @EBEBRATT-Ed , @JUGHNE , and @Jamie Hall for all for your extremely informative input. @Jamie Hall I cranked it up to 85 degrees and it still short-cycled.

I was able to troubleshoot a little with the boiler contractor. We determined that it was not pressure or the LWCO. The tstat wires were spliced to allow for testing the thermostat. I jumped the wires and the burner ran and kept running, so we determined that the problem is in the thermostat. I also jumped it at the thermostat and it worked, so it's not the old wiring.

I went out and bought a CT87K, which supposedly is the new generation of the T87 (correct me if wrong). I confirmed the W and R wires and put them in the terminals, but it didn't work even after multiple attempts and some fiddling. I read that this thermostat is poorly made and frequently fails to work especially when replacing an old mercury tstat.

Do you all have recommendations on what thermostat to replace it with? I'm a set-it-and-forget-it kind of guy, so I don't want a programmable. What I want is a tstat that's accurate and calls for head to the set temperature.

@Precaud : You mentioned that you got the Honeywell TH5110D1022 for your steam system. Do you still like it? (Summary: I'm replacing my moribund Honeywell T87 and I came across your thread: https://forum.heatinghelp.com/discussion/comment/1632506#Comment_1632506.)

Another option might be to fiddle more with my current tstat, but I don't really want to do that. I could also look for a new old stock T87; I've found some on Ebay.

Appreciate your thoughts all.

EBEBRATT-Ed

I had a CT87K at my house, all it had to do is pull in a relay, I liked it but after 2 years it started acting funny so I tossed it.

aat879

@EBEBRATT-Ed . Thanks. Don't know how to pull in a relay. It could be that the battery in it was dead; I had to ask the guys and Home Depot to pull it down from a storage box, so it was probably there forever. What, then, would you suggest I get? What did you replace your CT87K with?

Jamie Hall

Very odd. The mercury T87s are usually pretty darn near bulletproof. If it were me I'd probably hook the thing up to a convenient low voltage source and a low voltage light bulb and see if I could figure out what was wrong with it. And then fix it. But that's me. I like to fiddle with things, and simple contraptions which don't work are a challenge!

Unhappily, I too have heard some unfortunate things about erratic quality control on the new -- Residio I think -- mercury free mechanical thermostats (various types of "T87"s -- K, N, what have you). I would expect that the problem extends to most thermostats -- any manufacturer -- which use microswitches (as an aside -- the problem also extends to newer mercury free pressuretrols and vapoustats. This is called progress). Therefore...

The Honeywell Honeywell TH5110D series thermostats are regarded fairly well, and I believe most of them run off batteries. Various ones in the series have various "features"... some of the Honeywell Home thermostats seem perfectly adequate, too -- and are quite low priced (I just found a simple programmable after a fashion one on Amazon for $30...).

PC7060

@aat879 - I’ve got a couple old T87, where are you located?

Precaud

aat879 said:

@Precaud : You mentioned that you got the Honeywell TH5110D1022 for your steam system. Do you still like it? (Summary: I'm replacing my moribund Honeywell T87 and I came across your thread: https://forum.heatinghelp.com/discussion/comment/1632506#Comment_1632506.)

Yes, I like it a lot, it's perfect for my needs.

aat879

Thanks for responding, @Precaud . I'll consider that one. Also considering a couple of digital options with sensors from the same thread.

@PC7060 : I'll DM you. Thanks!

ratio

Bimetallic heat only stats are still a thing, they have real anticipators. The contacts are exposed (i.e. not a sealed microswitch, not a murcury bulb either unfortunately), not really much to go wrong with them. Might need to hit an HVAC supply house for them though.

mattmia2

Did you try moving the anticipator toward longer cycle times?

aat879

@mattmia2 . No. After putting up to 85 and having the same issue, I just resolved to replace the tstat before fiddling with the old one.

mattmia2

If the current draw of the controls is a lot more than the anticipator setting it will produce too much heat and shut the tstat off quickly if it is set at 70 or 85. It may take slightly longer at 85 especially when the call first starts but it is still going to run very short cycles

pecmsg

aat879 said:

@mattmia2 . No. After putting up to 85 and having the same issue, I just resolved to replace the tstat before fiddling with the old one.

You still don't know what's shutting the boiler down!

mattmia2

pecmsg said:

aat879 said:

@mattmia2 . No. After putting up to 85 and having the same issue, I just resolved to replace the tstat before fiddling with the old one.

You still don't know what's shutting the boiler down!

We know it is the thermostat:

aat879 said:

I was able to troubleshoot a little with the boiler contractor. We determined that it was not pressure or the LWCO. The tstat wires were spliced to allow for testing the thermostat. I jumped the wires and the burner ran and kept running, so we determined that the problem is in the thermostat. I also jumped it at the thermostat and it worked, so it's not the old wiring.

pecmsg

mattmia2 said:

pecmsg said:

aat879 said:

@mattmia2 . No. After putting up to 85 and having the same issue, I just resolved to replace the tstat before fiddling with the old one.

You still don't know what's shutting the boiler down!

We know it is the thermostat:

aat879 said:

I was able to troubleshoot a little with the boiler contractor. We determined that it was not pressure or the LWCO. The tstat wires were spliced to allow for testing the thermostat. I jumped the wires and the burner ran and kept running, so we determined that the problem is in the thermostat. I also jumped it at the thermostat and it worked, so it's not the old wiring.

Has the t-stat been bypassed? The heat anticipator can cause the same issue.

PC7060

@aat879 - sorry I’ve been late getting back to you some in expected travel has popped up. 

Both are a genuine Honeywells, although one has 3rd party label 

JUGHNE

At the USPS, I would just describe them as "electrical switches".
Any liquid and especially HG will throw up some red flags. FWIW

aat879

@pecmsg, it was the tstat. Replaced it with a simple Honeywell digital and it’s working fine.