Boiler short cycling?

Dianapagu · October 31

Hi All,

Im the past ive found the experts on this forum very helpful. Hoping again for that knowledge. As the weather starts to get colder its that time for the boiler to turn back on. In the past we've had our issues like not turning on completely leading to a replacement of the ignition box and pilot. This was 2 years ago. This time around we think its short cycling since it does turn on for a 1-2 min run and then it beeps calling for heat , turns on for a under a 1min then off/on all until the thermostat reaches its temperature.

This is a Williamson boiler to a one pipe system , steam gas boiler. We had someone come by to take a look but they didnt feel confident. Still suggest the ignition box ,pilot and gas valve be replaced

So im wondering does this somewhat sound correct. Trying to research short cycling on steam boiler and get lots other trouble shooting suggesting before having to do a complete replacement. I tired uploading the video but its too big. But any other advice would be much appreciated.

neilc · October 31

post a general picture, floor to ceiling, showing the controls side,

post a closeup on the controls and site glass, and gage while it's firing,

low water cutoff, pressuretrol, may need service,

EdTheHeaterMan · October 31

Does the flame light? YES = the ignition box, pilot and gas valve is working.

When it goes off you need to determine what is causing it. There are several things that can cause the flame to go out so quickly after it starts up. Most of them are electrical. Are you handy with an electrical meter? I can talk you thru the diagnosis process.

Jamie Hall · October 31

Before you even start thinking about the gas valve and ignition… there are a number of other things that could be the problem. Poor main venting (or non-existent)? (suggested by the initial short run 1 to 2 minutes is way too short for a starting run!). Low water level and surging causing the LWCO to trigger. Poor of otherwise inadequate radiator venting. Even poor near boiler piping… and that's for starters.

You need to begin by figuring out what is shutting it off.

EBEBRATT-Ed · October 31

Short cycling can have many causes. If it is ignition /flame proving issue some boilers will try to star 4-5 time before they lockout, so the flame can light…go out…light …go out.etc.

Other than that short cycling can be caused by the low water cutoff not enough water in the boiler or a surging water level.

Also could be the pressure control, it could be adjusted wrong or you could have a plugged pigtail.

There are other causes but those are the most common.

109A_5 · November 1

If you post your video on a web site that hosts videos and then post the link to it here.

Is the short cycling issue new to the system, that is it never did that before ?

Dianapagu · November 1

All things I have also thought of. I did notice the radiators closest to the boiler were not heating while the others furthest did. I dont think i have an electrical meter around but can definitely get one. The ignition box / pilot was replaced only 2 years ago unless thats how long they only last? Low water meter light isnt lite , smallest dim but i heard that was a "normalish" feature on Williamson. But the boiler is definitely full. Has it done this before? Not like this i want to say , only one winter we didn't get heat at all which is why I had an emergency service call done bc it was middle December and a weekend unfortunately but pilot wouldn't go off completely and company that serviced changed the ignition box n pilot for that reason.

Short video link here to view. https://youtu.be/uGI-CWdgn0M?si=xghWxldILpHoIh_1

109A_5 · November 1

What looks like the main burner drops out and intermittently the pilot stays lit and/or goes out then it restarts again. I'd verify that the 24 VAC to the Spark Ignition Control module is consistent and stable when the burner drops out. If the 24 VAC is good the Spark Ignition Control module is probably bad again. However before changing the module I would verify the flame sense rod is clean and there is 24 VAC from MV/PV to PV only when the pilot is lit.

neilc · November 1

loose wire, bad ground, somewhere there,

all spades snug? all screw type wire terminals tight?

somebody's loose,

Dianapagu · November 1

@109A_5 today we tried to clean the pigtail, it wasn't an easy one to take of so had to get a bit creative to get some slug out. Wiped burners off, not too dusty. This boiler doesn't have the traditional flame sensors I see when I search for an image. Its just the pilot like the diagram you added.

@Jamie Hall one of raditor closest to the boiler (#4airvent) wasn't getting warm at times. So I took it off when no heat was on valve closed and its slowly heating up where as the others on my floor #5 (lr/dr) already full of steam. Im going to replace the #4s and retry just so all radiators have new valves.

Uploaded another video from start of thermostat calling for heat to view. More of less the same as the first video. https://youtu.be/4rQdbYQ2OZU?si=XZoSdcA-4M3gTOtx

20251101_130903.jpg

109A_5 · November 1

Sometimes the ignition rod at the pilot is also the flame sensor. All depends on the ignition module and the boiler setup. Boiler model ? The high voltage will jump through contamination but the much more sensitive flame detection may not work correctly.

It seems the pilot is staying lit when the main burner is going out, which seems to me as odd behavior from the ignition module. The due diligence with a multimeter with a logical process that actually verifies the ignition module is actual defective should be done.

Also verifying all the electrical connections are physically secure should also be done.

It now seems like a similar failure to when the old ignition module was changed, which makes me wonder if something else is going on that was missed back then.

Dianapagu · November 1

@109A_5 some pictures to view. If its definitely the ignition module then ill have to start calling around for quotes/diagnostic but I think most things to troubleshoot have been exhausted. We're also going away next week and although it heats in the home may not be able to risk it giving out while we're away with tenants around.

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109A_5 · November 1

" If its definitely the ignition module then ill have to start calling around for quotes/diagnostic but I think most things to troubleshoot have been exhausted. We're also going away next week and although it heats in the home may not be able to risk it giving out while we're away with tenants around. "

Well without doing the troubleshooting due diligence it is just a guess. The ignition module is easy to change. Shut the power off, looks like a Philips screwdriver and maybe pliers for the electrical connections.

EdTheHeaterMan · November 1

This failure in the first video and around time stamp 6:23 on the second video remind me of a flame proving signal being lost. More than likely there is a ground path failure in the Flame Rectification path from the UTEC ignition control thru the flame back the the UTEC control That is common when a burner is connected to the rest of the boiler the way your burners are fitted. To be sure the ground path from the burner to the UTEC control is not corroded or compromised I run a physical ground wire from the pilot burner to the GND (BURNER) terminal of the UTEC Control.

Here is an illustration of the wire in place

This wire will eliminate any fault with the ground connection present from the burner to the control

The Steam Whisperer · November 1

Another common cause of short cycling is the thermostat. Occasionally the stat is bad, but often its not properly set up for steam or the electronic programming simply doesn't know what to do at light loads. I just changed out my Digital stat (lots of short cycling in 40F + outdoor temps on a high mass boiler and system) for a simple mechanical stat and the short cycling is now gone. Long burn cycles and I still have stable air temperatures. Old fashioned heat anticipators in mechanical stats often are much better than expensive digital stats.

109A_5 · November 1

I would think if it was a thermostat issue or a poor ground issue the pilot would always go out also, which it does not if you look closely in both videos. Maybe the dropout and recovery is too fast for the pilot to go out every time. Troubleshooting due diligent testing would prove what the actual issue is.

Boiler short cycling?

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