Boiler Short Cycling?

mculik5

I just upgraded from a Honeywell PA404A 1009 pressuretrol to a Honeywell L408J1009 vaporstat. The boiler is a Weil-McLain EG, and it's gas-fired.

I also upgrade the pressure gauge from a broken 0-30 PSI gauge to a Wika 0-20 oz gauge.

The vaporstat is currently set to break at 8 oz and make at 2 oz.

Not sure if this is relevant, but the house is about 1400 square feet, and steam is currently feeding to 6 radiators (house has 8, but I've temporarily removed 2 from rooms I'm renovating).

After hooking everything up, I tested the system. It took about 15-20 minutes for the system to warm up and the vaporstat to come into play.

Here's what I noticed once things were warmed up.

- According to the pressure gauge, the vaporstat breaks as set at 8 oz
- Once past about 7 oz, the gauge gets VERY jittery (worried this is going to harm the gauge over time)
- According the pressure gauge, the vaporstat makes at 5 oz; however, after the boiler kicks back on, the pressure continues to fall until about 2.5 oz (this would seem to indicate that the vaporstat is working as set, and the gauge reading is delayed, at least on the way down)
- All of the radiators heated up (so no need for more than 8 oz)

I timed the cycles, and am concerned that they are short (though this is totally gut feel, as I have no concept for how long the cycles should be). It took the boiler 1.5 - 2 minutes to get to 8 oz, and 30 - 45 seconds to drop back down to 2 oz. So - on for 1.75 minutes, off for 40 seconds, on for 1.75 minutes, off for 40 seconds...

Questions:

1. Is this short cycling? If so, approximately how long should the cycles be?
2. If this is short cycling, what can I do to fix it?
3. How can I prevent the pressure gauge from getting jittery?

Thanks!

KC_Jones

Those cycles are definitely short. The issue could be those disconnected radiators. You have effectively over sized the boiler by disconnecting them. Trying to tune and adjust your system with them removed will be difficult at best. If you want to get the system tuned in you need them back in service...otherwise you are basically going to have to deal with what you have. Once you have them hooked up the system will surely behave differently. You can either hook them up now to get the system tuned or just wait until your renovations are finished and tune it. In my opinion any work at this point is somewhat futile. In answer to your questions:
1. You basically want the cycle to be as long as possible or a better definition would be that you want to cycle on the thermostat and not pressure...if possible. This is in a perfect world.
2. See my comments above
3. Someone on here recommends the use of a gauge snubber (can't remember who) which give a cushion between the pressure and the gauge to smooth the operation. Perhaps someone with experience with these can elaborate.
Just another homeowner, but that is my take on your situation.

Jamie Hall

The person who recommended the gauge snubber is I -- and I do heartily recommend them. The jitters will be affecting the vapourstat as well as the gauge, and you really don't want them. They're cheap, and if both the vapourstat and the gauge are Teed off the same pigtail, you can get away with just one snubber. Go for it.

As to the short cycling. Part of it is surely the turned off radiators. You have effectively oversized your boiler by about a third, and as has been said you won't be able to do much unless and until you hook them back up. That said, however, is that 2 minutes to 8 ounces which you quote from the time that steam is first made? From when the burner fires up? Or from when the pressure gauge starts to move? It makes a big difference. If it's either of the first two options, you may be very very low on main venting. The pressure shouldn't start to rise -- well, maybe to an ounce or two -- until all the operating radiators are full of steam.

Can you clarify?

KC_Jones

Thanks Jamie I thought it was you that recommended the snubber.

mculik5

Thanks for all the replies. The cycle times I posted were taken after the system had warmed up and steam was starting to flow to the rads. More specifically, the pipes in the boiler room, the rad valves, and the first few sections of each rad were hot. My house was about 61 this morning when I was working on this. I cranked the thermostat to 70 to keep the boiler working. After about 30 minutes from the time I first turned the system on, the house was at 64, which is where we normally keep it during the winter.

The gauge stayed at 0 for a while after I started the system, but the rads were definitely not FULL of steam when the cycling started (they were beginning to fill as described above).

For what it's worth, my system has two mains - one along the front wall of the house, and one along the back wall. The pipes are ~2 3/8" in diameter, and both are vented with Gorton No. 1s. The front pipe is about 20 ft long, and the back pipe is about 35 ft. I want to replace them with No. 2s, as I've heard you can't have too much main venting, but both of the vents are in spots that make it tough to add anything larger without significant re-plumbing.

Thanks for the tips about the gauge snubber and two-stage gas valve. I will definitely look into both of those.

Fred

You have way too many variables going on to be able to balance your system. You need to re-install the 2 radiators that are disconnected to make the boiler closer to the designed EDR rating. You can't not tell if the system is short cycling (under normal circumstances) when the boiler is trying to recover from a 9 degree temp difference (61 to 70). Most boilers will start to short cycle when they are required to run long enough to recover from that kind of temp swing. You probably would be better sserved to set your vaporstat to cut out at about 12 ounces and cut in at about 4 ounces. Also, you could use at least one more Gorton #1 on each of those mains or if you have the head room Gorton #2 but I doubt that venting is the culprit here, just a contributing factor.

Mark N

It is code to have a 30 psi gauge on the boiler. Did you replace the broken one? What is the net EDR of the boiler you have installed? What is the EDR of all of your rads? What was the reason you replaced the pressuretrol? If you boiler is properly sized to your system you will most likely never cycle on pressure, you will always cycle on the thermostat.

Jamie Hall

Well, yes and no Mark. Even a properly sized boiler may cycle recovering from a very deep setback (you have to be so close to spot on, and the house temperatures have to be just so, and... the moon in the right phase, for all I know). But the OP is surely way over with his radiators taken out, so the "short cycling" which he is experiencing is most likely from that. As has been said, not much point in fiddling with other things until they are back in service!

nicholas bonham-carter

Even better than a snubber, which can get plugged up, and is difficult to clean, is the relocation of the gauge, and vaporstat to a tapping on the header. The usual location of a tapping into the boiler, is just to close to the surging water, especially before the 5th skimming.
Others may have had a good experience with snubbers, but not I. They are really better at evening out the pressure peaks of air compressor operation.--NBC

Mark N

Jamie, you shouldn't use deep setbacks with steam. But you know that. With a properly sized boiler that pressure cycling won't start until the rads are completely full with steam and unable to condense any more. This boiler started cycling on pressure with only the first few sections of each rad hot. I agree he oversized the boiler by temporarily removing rads. But, without the info on the system I asked for it is impossible to know if he made an already bad situation worse. Is the boiler oversized to begin with. That is a very common problem. What prompted replacing the pressuretrol with a vaporstat? Was the pressuretrol defective? Don't know without more info.

Mark N

We have no idea how the system operated with the pressuretrol. That info is not given. Might never have reached the cut-out on the presuretrol. He needs to get everything hooked back up, set the vaporstat to a higher cut-out and let the boiler run to maintain the 64 degrees they set the thermostat to. Observe and make note of what the pressure is when the thermostat is satisfied. With that info in hand choose a cut-out that won't cause excessive cycling on pressure when just maintaining temp. that isn't an efficient way to run the boiler.

mculik5

Again, thanks for all the info.

The sticker on the boiler says 254 square feet of EDR. Once all the rads are in, I'll have 238 square feet of rad EDR. Right now, I have 170 square feet of rad EDR.

How close do the boiler and rad EDRs have to be for the boiler to be considered properly sized?

Regarding the old pressuretrol, there is nothing wrong with it that I'm aware of. The reason I switched to a vaporstat is because I read on this forum that, aside from rad vents (which I'm also replacing), installing a vaporstat is one of the best things you can do to improve your steam heating system. We've always had water hammer, spitting vents, etc., and from what I read, a lot of those things are symptoms of high pressure.

Unfortunately, I never paid close attention to how the boiler worked before. When I tried to fix the broken pressure gauge last year, I believe I did see the boiler cycle on pressure, but I don't remember the specifics.

I'm in NJ, and fortunately/unfortunately, it's not cold enough here yet to really let the system run.

BobC

the boilers EDR should be matched to the radiators but in practice you often end up with more boiler than radiator. Once you reconnect those two radiators you will be pretty well matched.

If the Gorton #2's won't fit then use multiple Gorton #1's (or Maid O Mist #1's); It will take about 3-1/3 #1's to equal one #2. You can build a manifold to hold as many vents as you need BUT make sure the manifold has a little pitch so water can find it's way back to the boiler.

Bob

Jamie Hall

When you get those radiators re-connected, you will be close enough on boiler size. You may even be able to down fire it a bit to get even closer.

If you want an outside expert to give an eyes on look, talk to JStar (Joe Starosielec -- spelling -- sorry Joe) who posts here -- one of the best.

RobG

I agree with Jamie, if you can't get it figured out on your own call Joe at Thatcher HVAC (JStar). Use the "Find a contractor" link on the site.

Mark N

Your boiler is almost perfectly sized. This system should run with no issues. Pressure should be very low, all the steam your boiler produces should be condensed by the rads. Installing a vaporstat won't fix water hammer and spitting vents. Post some pictures of the near boiler piping. Also check your mains for proper pitch. Maybe a hanger has come loose causing a sag. Are the pipes hammering or is it in the rads? Are the pipes insulated? Make sure the hand valves are completely open. There are couple of good steam guys here in New Jersey. JStar is in the Metuchen area, Gateway is in Orange. Also it can't hurt to order Dan's books and learn for yourself.