Could a gas conversion (from oil) cause short-cycling?

DairyGodmother

Hi. I'm beyond a noob, and I have to ask my question in a general sense as I don't have the info handy.

This summer, I had my steam-savvy plumber install a gas burner on my 1- pipe steam system (5 year old peerless boiler, no model handy), converting from oil (which worked well, it was just a choice of replace oil tank or convert to gas.).

When he tested it then, it worked fine. But that was August. Now it's cold, and I went to the house (now vacant) to turn on the heat to prevent pipe freezing and it just cycles for about 2 minutes and shuts off. Then on, the off.

Plumber (who really is the local steam expert, our area has many homes from the 1920's) checked it once, and I heard from the painter that it was working to all but 2 upper radiators when he left. Then I went back a week late and I'm back to the 2 minute thing.

Now, as I have no info, and no photos, I don't expect anyone to solve this for me. What I'm trying to figure out is if this could be conceivably triggered by the gas conversion or if that has nothing to do with it. Is this new heat source really a separate thing from the boiler. I've read that oil fires much hotter and perhaps pressure settings are different for gas?

What I really want to know is if my plumber did the conversion wrong or is it a coincidental timing. It really had been fine in the spring. It has been cleaned and maintained each year.

I was always fond of my old steam system but I'm not sure I'll miss it!

Any help appreciated. I recognize it may be unanswerable.

Jamie Hall

If it worked with the oil, it should be possible to get it working again. It could be a control problem, but it could also be that the new burner is putting out more heat. One would need to know more, though, to get farther. How many radiators? How big? Firing rate of the burner? Any other changes or work?

DairyGodmother

No other work done at the time. 9 radiators in a 2057 sq foot house.

Answering your other questions will sound like an I Love Lucy episode :-p.

But I can keep track and take notes or photos in a few days.

Fred

A lot of questions need to be answered here. What size gas burner did he install? Is it comperable to the oil burner that was there? Did you have any short cycling with the oil burner? Did he measure the EDR of the radiators and adjust the firing rate of the gas burner to match the BTU's needed to match the radiation requirements as closely as possible? Are you sure is is short cycling on pressure and not on low water? Did he make any other piping changes (on the steam mains or near boiler piping) that may have introduced oils into the boiler water? When you look at the sight glass, is the water pretty stable (no more than 1/2 to 3/4 inch of bounce? Do you have adequate vents on the mains? (If you didn't have short cycling with the oil burner, that may not be the isssue but main venting reduces system pressures which is always a good thing and adds to fuel savings) Did he adjust the Pressuretrol or Vaporstat in any way? What is it currently set at? (should be .5PSI Cut-in and 1PSI differential for a Pressuretrol and about 12 ounces Main and 8 ounces differential for a Vaporstat). Do you know what the gas pressure is going into the boiler burner? Did he clean the flue, flue passageways and chimney?

DairyGodmother

What size gas burner did he install? Is it comperable to the oil burner that was there? -- can't answer but I'm pretty confident this was well handled. He'd worked with me for years, installed the old boiler 5-6 years ago

Did you have any short cycling with the oil burner? No.

Did he measure the EDR of the radiators and adjust the gas burner to match the BTU's needed to match the radiation requirements as closely as possible? Can't answer but again, I believe this was done.

Are you sure is is short cycling on pressure and not on low water? Water level is fine, glass clean and little bounce

Did he make any other piping changes (on the steam mains or near boiler piping) that may have introduced oils into the boiler water? Hmm... Not at the time, but I had an issue exactly 1 year ago when my oil tank got too low and some sludge got into the boiler and I had it cleaned. Interesting. Wonder if I should mention it? I had the oil provider fix that.

When you look at the sight glass, is the water pretty stable (no more than 1/2 to 3/4 inch of bounce? Yes

Do you have adequate vents on the mains? (If you didn't have short cycling with the oil burner, that may not be the isssue but main venting reduces system pressures which is always a good thing and adds to fuel savings). No reason to doubt

Did he adjust the Pressuretrol or Vaporstat in any way?-- don't know...

What is it currently set at? (should be .5PSI Cut-in and 1PSI differential for a Pressuretrol and about 12 ounces Main and 8 ounces differential for a Vaporstat). -- I will check this if I can figure it out

Do you know what the gas pressure is going into the boiler burner? -- no, I wonder if I can check this

Did he clean the flue, flue passageways and chimney?-- had flue/Chimney swept, city inspectors checked as well, forgot to mention that


Thanks for putting time against this. From the questions I'm getting my answer sound like, yes, he could have improperly done the conversion

Fred

Sludge from the oil tank would have affected the oil burner but not the water quality in the boiler. sounds like the water in the sight glass is stable and that no other work has been done on the steam pipes that may have introduced oils into the boiler water. I'm guessing the gas burner is probably somewhat over-fired for what you need and that he may need to down fire it some.

icesailor

If it is cycling every 2 minutes, I would be looking to see if the burner control is causing the cycling. If the steam pressure isn't being satisfied, then it isn't shutting off on high pressure setting steam.

If those Carlin/CCT type controllers even get a passing thought that there is a problem with the flame, they shut off, wait two minutes or some decided interval and try again. Two minutes running is about long enough for something to develop and stop the burner. Check the Ohms from the flame sensor.

Depending on the unknown Peerless oil boiler, it might have a short chamber area.

jerryjjj

I just read some articles this morning. Avoid oversized gas boilers because oversized boiler will be less fuel efficient and will cause short cycling.

DairyGodmother

OP posting much later, we had multiple issues before it was fixed, a bad thermostat, a bad sensor (I forget the name of it but it was dirty and it senses if the gas is lit), and one more thing I forget. Thankfully the plumber only charged me for combined labor not each house call to figure it out!

Mark Eatherton

Don't throw the plumber out with the bath water yet. You have a fairly maintenance intensive system. Lot's of things to go wrong, and only takes one going bad (or more) to cause the symptoms you're seeing, and as everyone has pointed out, they all have to work in harmony, or it's short cycle city.

A good and thorough due diligence study, and recommended actions report would go a long ways towards not wasting time and money and causing even more frustration. With a good qualified technician, it should be a snap. If your plumber has any questions, send him here for answers. The price is right, and well worn/tested advice is free.

ME