Causes of late cycle reboots before "call for heat" satisfied

Daniel_3

Been a looooooong time since I posted here! Hope everyone is doing well this New Year!



A couple questions regarding my Burnham IN7 which has suffered from a possible normal phenomena. Shortly before the call for heat is satisfied on colder days the burner shuts off and back on probably in upwards of 15-20 times before the end of the cycle. This is a one pipe steamer with dry returns.

1.) Honeywell Electronic Ignition Q348

2.) McDonnell LWC

3.) Honeywell pressuretrol on a pigtail

4.) Drop header with both supply taps used into a 3" equalizer

5.) Some fancy 5+2 Rite-temp thermostat

6.) Auto close flue damper



So I'm posting here because I believe the controls are to blame ( if indeed there is a problem at all). I had this issue crop up last year (nary an issue before this year and it's been installed since 2007) and after replacing the rollout switch things seemed to be fine afterwards. This year I jumped the rollout after I experienced it again and the cycling still happened so I can't really put my finger on what's causing this. Pressure is set to 1.5 main and .5 differential. Is the pigtail slightly clogged? Does the EI probe need to be replaced? The flame is blue and steady. The Nstar tech came out last season and did a pressure check which yielded about a >10" column? Basically he said there's plenty of gas(after he turned on all the stove burners and hot water heater concurrently). I pulled the pilot assembly the did not check the ground or the gap for the spark as of yet (gotta get my feeler gauge in there for .125, right?) but did wipe off a bit of white residue(ash?) off the EI probe tip which faces the flame. The LWC is getting plenty of water height, no errors there. Being that it occurs at the very end of the cycle I believe it must be a pressure issue, no?



A little stumped indeed! Thanks all!

Jamie Hall

Almost certainly

pressure.



But before I go any further, if you haven't reconnected that roll-out switch, go downstairs and do so.  Then come back and read the rest of this.



What you are describing is quite normal if the boiler is slightly oversized and if it has to run a long time for some reason -- particularly coming out of a deep (which I define as anything of 3 degrees for steam) setback.  What happens is that after a while the radiation is completely filled with steam, and is condensing just as fast as it can possibly do it.  The boiler, however, is producing slightly more steam, so the pressure rises.  The pressuretrol does exactly what it is supposed to: shut off the burner.  Then the steam continues to condense, and when the pressure has dropped far enough the boiler comes back on to give the system another shot of steam.  This balances the steam demand in the radiation with the steam production in the boiler.  This will keep going until the thermostat is satisfied.

nicholas bonham-carter

Short-cycling Burnham

I am assuming this is a steam boiler, because of your reference to the drop header.

This may be a main venting problem, which if you have a 0-3psi gauge, can be seen from that reading.

If the main(not rad) venting is inadequate, then the boiler will cycle off and on while forcing the air out of the boiler, and pipes through non functioning, or little main vents.--NBC

Daniel_3

Thanks Jaime

Super fast response Jaime, thanks!



I had done due diligence when installing this and left over just enough sqft. edr to cover one more future radiator in an attic. Total EDR in my house currently used is about 527 and this boiler handles 544 if I remember. I even did my own riser diagram for venting purposes. Being that this only occured last season due to the roll-out (Yes that was reconnected after the test early in Dec. when I did it) switch failure and this season It must be related to another issue regarding pressure, no? I would expect that it would have happened from the get go when it was installed in 2007.

Daniel_3

Hi Nicholas

Yes it's steam. Main vents were done up with the rest of the system when I delved deep into dead man territory in 2006. I did do a riser diagram as included in the previous post for venting purposes. There are three Gorton no.1's on one supply end and 2 Gorton no.1's on the other supply end. The thermostat calls for heat at 67, is set to 68 and the heat in the room will rise to 70 after all is said and done.

Daniel_3

Pressure

I did reply below though not attached to this post. The on/off is quite immediate. It will shut off/on almost instantaneously like 6 or 7 times then on for a few minutes then maybe more immediate on/offs for 10 times, then on for the end of the cycle. It's not very consistent but there is barely a second between the on/off cycle 90% of the time on these cold days. Essentially I'm concerned with wear and tear as this happens and not with the ability to get some good radiation

Jamie Hall

One possible problem

which I have encountered -- which you may have -- is that vapourstats are both very sensitive and very responsive.  It is quite possible that it is responding to small peaks in pressure (the pressure is never constant) and giving you false trips.



The best way to solve that problem is to place a snubber (http://www.omega.com/pptst/PS_SNUBBERS.html for examples)  in line with the vapourstat.  It can work wonders...

nicholas bonham-carter

Rapid cycling

It almost sounds like a gas valve problem, as the pilot continues to be lit, and the gas starts and stops on its way to the burner.

Can you look into the burner assembly and see if the pilot remains lit.

Cycling on some other safety would require the pilot light to be proven, and take a longer time between cycles.--NBC

Daniel_3

Snubber

A great product and possible solution. I will definitely look into that. If I were to raise the pressure back up to bonehead territory I might be proving the issue through a full cycle, right?

Daniel_3

Gas

Definitely stops and starts. I will come back to you after checking tonight for whether the pilot stays lit or not. I believe it stays lit, mayeb  for a split second. The burner on/off happens very rapidly within 1-2 seconds. The damper never closes. The *whoosh* of gas never happens (unless the on/off cycle is overcome somehow) for all burners to be on full. I do get the initial *poof* (for the pilot?) of gas then a clicking on/off sound, then another *poof*, then the click clack again, then the *poof*, etc, etc. It doesn't sound like the EI is firing during this on/off cycling. That's a tell tale sound for me.

Basically I'll go take the plate off and observe closely tonight when I get home.

nicholas bonham-carter

Stuttering system

Check the wiring to the gas valve on the control side, and see if there is a loose connection.

As I said, if the other safeties were cutting out the burner, there would no doubt be a longer interval between the relighting of the burner, as the pilot is proven.--NBC

Daniel_3

Video

For your viewing pleasure. So the whole cycle does reset: Spark to pilot to gas vavle fully open to all burners igniting.

http://youtu.be/TkELPe-4F4Q

nicholas bonham-carter

Time to relight

Compare the time to relight when you flush the LWCO, or briefly switch off the boiler, and see if that time to relight is longer than the relights you have now. I would think there would be a longer interval, but this would show any difference, when the pilot light has to be relit, and proven.--NBC

Daniel_3

Will

do, thanks for your insight Nicholas. By "flushing" the LWCO do you mean just dumping the water from the hartford till it trips, then refill for reset? I'll try the boiler switch as well.

Jamie Hall

If you have

a float type LWCO -- such as McDonnell Miller -- it will have a drain on it, at the bottom, with a valve.  That type of LWCO does need to be flushed now and again -- opinions differ on how often, anywhere from weekly to monthly -- to flush the goop which accumulated in the float chamber.  Just open the valve (into a bucket!) until any real goopy goop is gone; usually a gallon or so will do it, or even less.  The water will not be clear, but better.



Probe type LWCOs do not have this, and do not need flushing.



I still think a snubber will help you more than almost anything...

Daniel_3

Probe

Type is what i have. I did flick the switch on the boiler and after the manual reset on the LWCO was reached, the damper resumed an open position after closing, the gas valve opened, the EI parked, and the pilot fired with a *slightly* longer proving than what the video shows before the gas valve opens fully.



Once thing I did notice when I took the video is that the burner flames did appear quite orange for about 5-10 seconds during one of the end of cycle on/off situations. I'll try the snubber for sure and see what happens next. Thanks for the wealth of experience guys.

Daniel_3

Wow.

Just saw a "NoShok" brand snubber with the four sized pistons . . . .$45?! Pricey for a piece of  1/4" bras.

nicholas bonham-carter

Test before buying

Use a jumper wire on the pressuretrol to confirm that this is a pressure problem. This will temporarily prevent any spikes in pressure from causing a burner shutdown, by disabling the pressuretrol.

You could probably achieve the same result with two pigtails in series, ironing out any pressure fluctuations , and easier to clean than a snubber.--NBC

Daniel_3

Just wanted to resurrect this thread as I did put two pigtails in a series. I will say that this short cycling as viewed on the above you tube video does happen but not every time since I started up the boiler this season. I didn't try to jump the pressuretrol. I haven't jumped the pressuretrol yet as the burner cycling did not occur today after changing the pigtails. Thanks guys and I will continue to monitor the issue.

Abracadabra

Main flame sensor needs cleaning or replacement?

Had this exact scenario with a laars boiler. Flame sensor needed some careful cleaning and it was fine.

Daniel_3

After re-reading this post I would reaffirm that the relit of the burner is super quick and the pilot is still proven as the video shows probably proving that it may wind up being a gas valve/gas supply issue. When this happened last year a Nstar gas tech came to test the gas supply at the meter and said it read 10 bar (if I remember correctly as my measurement in bar may be in error) showing that the supply at the meter was well within limits. I believe it should be between 7 and 13 bar?

icesailor

If it were an oil burner, I would be having pressure gauges at both sides of the fuel pump. To see what the pressures are.

A gas regulator is like a fuel pump. Have you tried checking both sides of the regulator for pressure when this happens?

Just because the gas guy checked and found plenty of gas at the meter and turned all the appliances on, doesn't mean that it stays like that always. If the incoming pressure doesn't change when it is running or cycling, wouldn't something be causing the valve to operate?

Sounds scary.

Daniel_3

I've not tried checking pressures before and after the regulator. I certainly agree with your assessment of the overall pressure at the meter and certain appliances not wholly precluding an issue with the gas regulator on the boiler.

I'm not sure what you mean by the incoming pressure not changing and the valve activating closed relating to another source though. Do you mean the gas step valve or something else and by "operate" do you mean it closing in response to a dangerous situation?

Do you mean to say it is caused by a bad pilot assembly or powered vent assembly? Some other safety feature being tripped? What sounds scary about it?

Daniel_3

I'd like to add the fact that this issue cropped up on the beginning 1/3 o a heating cycle as well, not just toward the end.

Abracadabra

Abracadabra said:

Main flame sensor needs cleaning or replacement?

Had this exact scenario with a laars boiler. Flame sensor needed some careful cleaning and it was fine.

This ^^

Daniel_3

Missed your flame sensor idea Abracadabra......I did take the pilot and associated parts out to clean with a bristle brush(carefully of course).

Tim McElwain

Pull the pilot and clean the pilot and also clean the flame rod. Is this a single rod pilot or a dual rod pilot? Once you clean everything when this starts happening be connected up and check the microamps they should be between 2 to 10 microamps 3 to 5 is normal.

Abracadabra

Daniel said:

Missed your flame sensor idea Abracadabra......I did take the pilot and associated parts out to clean with a bristle brush(carefully of course).

I'm not talking about the pilot sensor/thermocouple. I'm talking about the main flame sensor. Should be 2 different things.

Daniel_3

Tim, it's a single rod and I'll also try the gas valve side thermocouple brass nut connection too. I believe the wire on the inside might need a double check, maybe a light sanding.

Abracadabra, isn't the thermocouple the flame sensor? Ie. the thing that lets the gas valve open fully after the electronic pilot ignition?

Daniel_3

I guess the proper term would be flame sensor as this is not a standing pilot? Thermocouple for standing pilot?

This assembly has the red rubber wire, pilot tube, and "soldering iron" looking sensor adjacent to the pilot hole.

Abracadabra

Daniel said:

Abracadabra, isn't the thermocouple the flame sensor? Ie. the thing that lets the gas valve open fully after the electronic pilot ignition?

No. Flame sensor has a spark plug boot/wire on it.

Daniel_3

Then that's it and I don't have a thermocouple.

Abracadabra

I just read back thru the whole thread. Burnham IN7 does not have a main flame sensor. Since this is a spark ignition, either the pilot flame sensor is not getting properly hit with the pilot flame or there is a ignition module failure. This doesn't look to me to be a pressuretrol or LWCO shutdown on the burner. I think the IN7s also have a disc thermostat on the vent hood as a safety. Could be that's flaking out? Also verify good power output on the transformer.

Daniel_3

Thanks! I'll look into those things. I believe there should be a swicth on the hood to maintain the open position......a black one maybe? As I type I'm not at home to check. The issue has not cropped up since the last mention of it a few days ago.

Daniel_3

null
Abracadabra,

Your suggestion of the ignition module was the case. All other safeties checked out a-ok: lwco/ pressuretrol/ high temp sensor/ flame rollout/ gas valve/ pilot assembly/ vent damper/ transformer/ and ignition wire. I have a new thread in "Controls" that I probably should have added to this one. Consider this thread solved! Thanks again my friend!

Abracadabra

nice...