After reading through dozens of posts here on "the wall" relating to the venting of steam radiators and their supply mains.....I am stumped and need some expert advice. I will try my best to include everything that is usually required (including pictures) to provide you with everything you may need to offer a opinion. I apologize for the length but hopefully it will cut down on questions you may have.
A little history:
130 year old House in Central Massachusetts
One pipe Steam radiators (all different sizes)
3 on first floor, 4 on second floor
Installed New Oil fired Steam Boiler (in basement) about 7 years ago (info shown in pictures)
Most of the radiator vents are adjustable heat timer vari-valves
Problem: during start up in the morning from a temp of ~62 deg F to 68 deg F, the boiler runs until all radiators are heating each room, but when it is still a few degrees from the set temperature, pressure builds on the boiler gauge to around 1.5-2.0 psi, and shuts off. About 1 minute later the pressure gets to the cut in setting of 0.5 psi and starts again. After about 2-3 minutes the pressure rises again and everything repeats itself. This can happen about 10-15 times before the remaining 2 degrees of the temp setting is reached and the boiler shuts off.
This just started happening recently. It seemed to coincide around the same time I put a new "nest" thermostat in the house. For reasons I will explain later, I do not think the Nest is related to the issue. One thing the Nest has shown me is my daily usage in a graph that confirms the off and on sequence every morning.
The first thing I did was remove all the vents from the radiators and soaked them in hot vinegar for 30 minutes, then rinsed them and re-installed them. Before I installed them I blew through each one to make sure I had air coming out of the vent, they all seemed fine. I figured if they failed to shut upon getting up to temp then the worse thing would be I would have more venting than I wanted which would only help my issue. The same problem existed after that. After reading through these forums I saw the mention of "Main Vents". I though "i've never seen any in the basement". So I went looking.
There are 2 steam mains coming off of my boiler. One runs about 12 feet with 3 radiators coming off of that run. 2 radiators feed the first floor and one goes up to the second floor. I'll call this the short run. The other main runs about 50 feet in total length around the basement and feeds the other 4 radiators, 2 on the first floor and 2 on the second. All 7 radiators heat without any problems.
So I find that there is NO main vent on the short run anywhere, even though I have had no issues for all the years I have lived here. The other longer main DID have a 3/4" vent at the very end of the long run. I didn't know this because it was in the back of my workbench peg board, which of course only had enough room to "squeeze" in there to remove it. It did not appear to be working (no air came out when I blew in it), so I contorted by body in that tight space to remove the valve, soaked it in hot vinegar for 30 minutes and was able to get a "little" air to pass through it. I re-installed it........next morning same problem.
Next I bought 2 new Gorton air vents. I couldn't fit the Gorton #2 behind the work bench so I installed a Gorton #1 in that location.........next morning same problem. The next night I tried to remove the plug from the end of the short main only to find out that the dead men must have had no desire to see it come off. Even with heat and a 3 foot pipe wrench it wouldn't budge. So I drilled and tapped a 1/2" hole in the side of the short run near the end and installed the Gorton #2 vent. After reading through these forums there was always mention of never having enough vents. So now I had a new Gorton #1 vent in the long run, and a brand new (for the first time) Gorton #2 in the short run. I also had all the previously cleaned Vari-Vents in the wide open position on all radiators............next morning same problem. I may have gone from 15 short cycles to 10, but still had multiple short cycles.
My pressuretrol is set for 0.5 cut in and ~1.5 psi cut-out. The pressure gauge (mounted in a separate location) will slowly read pressure and when it gets to a little over 1.5 psi, the burner shuts off, about 3 minutes later the process starts all over again. So I don't "think" I have a problem with my pigtail unless I concidentally also have a problem with the pressure gauge.
The water in the glass is clean, although when I blow down the low water cut-off each week it does get tinted a bit but clears up quickly. It only bounces in the glass about 3/4" maximum when the boiler is at 1.5 psi and ready to shut off.
Regarding the "Nest" thermostat. I have read all the pros and cons on this high tech gadget, but I have had no issues whatsoever and it seems to be working just fine. I only have 2 wires (red and white) going to the Nest, which is 2nd generation Nest so there should be no need for a "C" wire.
Now I did move the thermostat from the dining room (where there is a radiator) to the kitchen, where there is not a radiator. There is however a radiator in the hall about 8 feet from the thermostat and there is only a difference of about 2 degrees from what the old thermostat reads and the Nest. (even though the old thermostat is not hooked up to the boiler, I left it in the dining room to watch the temperature difference). When the thermostat was in the dining room I had it set for 70 degrees at 5:00 a.m. Because there is a 2 degree difference in the Nest and this old thermostat, I set the Nest for 68 to get the same results.
To make sure that the nest didn't interfere with the cycling of the boiler, I turned "off" the"true radiant" learning setting on the Nest. This feature learns how long your system takes to heat up and uses that info to create a predictable schedule with even heat. It works with in floor radiant as well as traditional radiators. I thought maybe this was somehow "preheating" the system but after getting up at 4:30 this morning to watch the short cycling unfold, I confirmed that it is in fact shutting down on the set cut-out pressure by watching the pressure rise on the gauge to ~1.5 psi.
I was considering buying all new vents for the radiators, but didn't know if that was still feasible considering all that I have already done. The main vents obviously allow the mains to vent and heat up quickly but all the radiators also heat up as I remember them doing before. I realize that even without the one main vent working and the other nonexistent, it required the radiators to vent the system, so if anything I have sped up the steam to the radiators, but perhaps they are still not venting enough before their respective vents close upon receiving steam?
When I installed the boiler about 7 years ago, I removed a radiator from the kitchen. I blew out the wall and put in a sliding door leading to an outside deck plus the kitchen was always hot anyways. The boiler may be a bit oversized by me doing that, but I have never had this problem before, not for the past 6-7 years anyway.
So now I am considering the purchase of all new vents for the radiators (spent all my money on the 2 Gorton vents!) or cleaning out the watersides of the boiler (really don't want to unless I have to). I have also considered removing the pressuretrol and cleaning the siphon, but the corresponding pressure gauge seems to match what the boiler is doing so not sure if that is feasible either. I blow the low water column down at least every week, sometimes much more. The boiler is cleaned every year and is still in very excellent shape.
Other bits of info:
The combustion chamber in the boiler could use a new floor because it is starting to flake when I clean it (even though I am careful).
The Gorton #2 on the short run is as high as I can get it because of the floor above.
The Gorton #1 in the long run is not perfectly straight up, more of a 45 degree angle. I had no choice as you can see from the pictures.
I replaced the vent in the radiator closest to the new thermostat with a Maid O Mist (size C), which has higher venting, to get more heat to the thermostat in hopes of satisfying the thermostat quicker to avoid less short cycles.
All pipes are insulated in basement except for the new Gorton 1/2" line (doing that this week). Some piping going up to the 2nd floor are uninsulated but they have always been that way.
The nozzle in the burner is either a .80 or .85 GPH. I think maybe .85 with a 80 degree. Either way it is the same it always has been since startup.
I had a squirrel in my attic a few weeks ago that I had to have removed, but I don't think he knew enough about boilers to make any changes without my knowledge.
THANKS in advance for any opinion or comment you may have to get me back to the way things used to be......at least with my steam heating system.
Have a look at the pictures. I hope I have included everything important. Sorry some of the pictures are not properly aligned. They uploaded correctly but after publishing them they were rotated. I tried rotating them and re-publishing, but they are still rotated 90 degrees??