Short Cycling

Terry_15

Thanks, I'm assuming you mean the vapor stat? If so yes.

Terry_15

What do I look for next, do to boiler short cycling

I'm really struggling with my short cycling boiler. I just installed three #2 Gorton vents today, and I had hoped to see some difference. Have also added a vapor stat and orifices at each radiator valve. First call for heat the boiler will run around 15 to 20 minutes and then it will begin running 30 seconds on, 45 seconds off. The boiler was replaced five years ago and is over sized by 125,000 (350,000) btu. So I've down fired the boiler by removing two burners (50,000btu.) and turned back the gas valve two complete revolutions. What to do next? Is my only option to replace the boiler, with a proper sized unit. I'm starting to feel it will require a second morgage to pay this winters heating costs. Any thouhts would be appreciated.
Thanks so much!

Mark Hawkins

This may be a dumb question but did you check the pressuretrol to make sure the cut in and cut out are far enough apart? I would set inat .5 and out to 1.5 to start.

Tony_23

It seems

you may still be oversized by 75000 ? How did you determine how much you were oversized ?

Also, how many burners were there to start with ? I'm thinking each burner must be more than 25K ? At 25K each that would be 14 ?

Don't adjust the manifold pressure of the gas w/o a manometer. Fewer burners does NOT mean less pressure required.

What is your vaporstat set to ?

don_156

I

wonder does the return come back wet or dry.Even with orfice valve they still need a waterseal or a trap to keep
steam from going into the return.

I guess what I'm trying to ask is...Has it always been a vapor system?

Terry_15

Yes, Don it has always been a vapor system. We have added the orifices to work with the water seal traps, do to the original graduated heat control valves were replaced with newer valves sometime ago.

Terry_15

Thanks Tony

Yes there are 14 burners @ 25,000 btu each. A company I have been using had done the required calculations from the total square footage of radiator and supply piping, to determine the propper sized boiler required.

The vaporstat is set at 4oz with a differential of 2oz.

Thanks again!

Tony_23

There you go

Vaporstat setting ought to be 12 oz and 8 oz diff. IMO

Terry_15

Tony, not sure I understand? Most post I've seen say 4oz and 2oz diff. for vapor systems? I will give it a try! Also what did you mean by IMO. Thanks again!

Tony_23

IMO

In My Opinion

mel rowe

Tony, are you speaking of short cycling,as the system starts up after having being shut down for awhile by the stat, or cycling on pressure as the vaporstat kicks in and out? If it's cycling on pressure off the vaporstat, I have been told that is not a bad thing to have. That's just minimizing the burner-on time until the system achieves the 'stat setting.

scott75

Is the thermostat maintaining room temp? If you dail the vaporstat up to run at a higher pressure, will the burner stay on longer then? Is there a flame sensor the burner can be short cyclying on that is dirty and can be cleaned with sand cloth? Just some ideas?

Tony_23

ask Terry

it's his boiler

Terry_15

Thanks all....for your help!!!

Yes, it is short cycling on pressure after the thermostat's initial call for heat. I've raised the vaporstat pressure settings from 4oz and 2oz to 8oz and 4oz, which has made a big difference. I will check and clean the flame sensor next. Thanks again!
There's something new that I may have uncovered. To install the new Gorton vents, I had to remove some wall covering material. This revealed the wet return, and after reviewing it, I began taking some measurements. I'm questioning the horizontal union height in relationship to the boiler water line height. This would be between the supply and return after they transition to vertical before becoming a wet return. This union is currently 5" above the boiler's water line, and I'm thinking at this point it should be part of the wet return to keep steam from crossing over into the dry return and also to help keep the pressure up for a longer period of time. Again, thanks!!!