System Short Cycling - Steam Heat

ecullina

I have a two-family house. I just had new gas -steam heat boilers installed.


Unit one runs for about 35 minutes and then short cycles. The plumber who installed them has been making adjustments to the PressureTrol. The Main is set at 2 and now the Diff is set at 1.5. The system runs better than it did at the original setting of 1.0 Diff. They changed all the vents on the radiators. Even replaced the PressurerTrol yesterday

Given that after all these changes the system still Short Cycles I wondered if you had any suggestions on what else could be done? Can the Pressuretrol be adjuster further to allow a longer cycle time between restarts so the pressure in the system has more time to let the heat from the steam pressure to heat the apartment before turning back on?


Example of the latest heat cycle :

Current Temperature = 62 raise heat call to 65 system call shuts off at 66
After running for 24 minutes temp = 62
After running for 34 minutes temp= 64
After running for 38.47 the system short cycles the temp = 64 boiler pressure 2.5 psi when it shuts down
System restarts at 41.00 minutes temp = 64 Boiler pressure = 1 psi
After 46:40 system short cycles temp = 65
The temperature rises to 66 before the boiler needs to restart

Any suggestions would be appreciated.

Could the boiler be oversized and causing the pressure build-up ? 140BTU Burnham PIN5

Note: had oil previously and did not have this issue.

Signed

ED

KC_Jones

There are many possibilities. Oversizing is a common one and I wouldn't rule it out. If you want to check it we can assist with the calculations, or walk you through it as it's fairly simple. Below is a link to the guide I have used, it covers the typical rads, but if you have something that doesn't match post it here and someone may be able to look it up for you.

https://www.weil-mclain.com/sites/default/files/wm-boiler-replacement-guide.pdf

Start on page 9 for steam

Jamie Hall

In your first post, @ecullina , you mention hot water radiators -- but this is posted in steam heating, so I'm a little confused.

However, my question is still relevant. On those short cycles, what is controlling the boiler? Is it the thermostat turning it on and off, or is one of the boiler controls turning it on and off? It makes a big big difference in how to attack the problem.

EBEBRATT-Ed

@ecullina

You need to check the boiler versus the radiation load size as @KC_Jones mentioned. And post a few pictures of the boiler installation

FrankB101

"However, my question is still relevant. On those short cycles, what is controlling the boiler? Is it the thermostat turning it on and off, or is one of the boiler controls turning it on and off?"

You would have to be able to troubleshoot that situation. If you know how using a voltmeter would be the best method or temporary jumpers could be used to determine which control has shut it off.

ecullina

Jamie,

The Pressure in the Boiler reaches 2.5 PSI and the Pressuretrol shuts it down. The thermostat call for heat is still in place since the temperature requested is not yet achieved

The reference to Hot Water Heater was an error . Everything is steam

ecullina

Here are some pictures of how the boiler is piped:

ecullina

ecullina

Jamie Hall

ecullina said:

Jamie,

The Pressure in the Boiler reaches 2.5 PSI and the Pressuretrol shuts it down. The thermostat call for heat is still in place since the temperature requested is not yet achieved

The reference to Hot Water Heater was an error . Everything is steam

OK -- no problem, and not that unusual. Cutoff pressure is a bit high -- it would be better all around (and save fuel... and money...) if that could be lowered to around 1.7 psi. Leave the left scale -- differential -- set at 1, and just turn the screw on top above the right dial down to 1.7.

It will still cycle on pressure -- that's an indication that the boiler is bigger than it needs to be to feed all the radiators, and it needs to stop for a little time to let them catch up.

Canucker

@My570 It's megapress. It's approved for low pressure steam temperature but no one on this board, for good reasons, wants to be the guinea pig for that testing. 

ecullina

EBEBRATT-Ed

Looks to be a counterflow system. Idon't get a good idea if it has the required drip or not

ecullina

The pipes in cellar are recently insulated ( removed the old stuff)
Each unit has its own section of chimney and each has a new liner
Unit 2 is larger ( two levels above Unit 1) . Unit 2 has 9 rads and Unit 1 has 8.

They have come back and said unit 1 is over sized . ( The plumber brought in a person from the manufacturer who checked the sizing . Says other than the sizing the unit is performing the way it should )

They suggested making an adjustment to the amount of gas feeding the burner . One concern they mentioned was that lowering the gas could cause some soot to build up and that would be an issue .
This made me wonder if it would shorten life of new liner just installed ?

This soot concern has me worried . Thinking that the short cycling is less of an issue than the problems that could result from lowering the gas /flame .

Let me know if this is a valid concern and if there is anything else that might be considered .

ethicalpaul

Did you try stopping the setback? In your first post you are trying to raise the temperature several degrees. Don't do that. Just set it and leave it to minimize cycling on pressure.

Did you put your pressuretrol back down? Boosting pressure to make the system "run better" is a myth. You're just burning fuel for nothing. Short cycling is better than that.

ecullina

Yes, I did stop setting it back. It helped a little but once the system warms up the system tends to short cycle quicker. when the system cold it takes a while for the pressure to build up before it will short cycle. sometimes it does not. But once the system is warm it short cycles after running 20 to 30 minutes

ethicalpaul

Does it run for 20 to 30 minutes during a normal call for heat?

How many cycles does it take to satisfy the thermostat on a normal call for heat?

Did your installer measure and add up all your radiators to determine the correct boiler size to install?

Do you have correctly-sized and operational main venting?

ecullina

It runs about 35 to 45 minutes and the rads all get hot but tends to shut down just before achieving the heat level requested .

It can take 2 to 3 cycles to achieve heat level. Cold start seems to have less short cycles . When the system is warm and call for more heat it seems to short cycle more.

They re-measured all the rad last week and now say that the system is larger than what was needed ( one step below would have been enough)

The replaced the main vent and it seems to be working ( you can hear the air escaping at the beginning of the cycle

mattmia2

1 minute off, 5 minutes on doesn't seem bad. Maybe you need to replace the gas valve or ignition control after 20 years instead of 40.

pecmsg

Get a Low Pressure Gauge for accuracy. 0-3 or 5#'s

https://www.supplyhouse.com/Winters-Instruments-PLP305-2-1-2-PLP-Steel-Low-Pressure-Gauge-1-4-Bottom-NPT-w-Brass-Internals-0-5-PSI

Jamie Hall

mattmia2 said:

1 minute off, 5 minutes on doesn't seem bad. Maybe you need to replace the gas valve or ignition control after 20 years instead of 40.

Quite agree. That cycle timing towards the end of a longer run, such as coming out of a setback, is actually quite normal.

ethicalpaul

Yep not too bad really. If it cycles like once or twice at the end of a normal call for heat, I wouldn't lose sleep. Actually I would because I hate it when these systems build pressure. I would (and did) install a delay relay that activated whenever pressure got up to a couple ounces, but I'm not normal.

They re-measured all the rad last week and now say that the system is larger than what was needed ( one step below would have been enough)

Shocker! Measure twice, install a boiler once. Did they refund you the difference in price? Or at least act kind of embarrassed?

No one has answered your question about downfiring. I have tweaked my gas pressure on my old oversized boiler but I wouldn't recommend it unless you have a technician you trust (maybe not your guy) who can do a combustion analysis. You really don't want soot buildup in your atmospheric boiler, nor excess CO production. You want a tech who will be patient and will watch the boiler behave as he minimally and carefully adjusts the pressure in order to reduce the steam pressure buildup during a normal call for heat. This will require several heating cycles to do right IMO.

Overall your guy didn't do too badly IMO. The piping looks OK. People might not like the propress or megapress or whatever he used but the header looks correct so you should have nice dry steam. Don't worry much or at all about inefficiency. Basically 80-some percent of the BTUs that this boiler creates will go into your house, and 15-some percent will go up the chimney. Nothing is going to really change that. "Short cycling" on steam boilers (really "cycling on pressure") isn't really a big deal compared to some other systems.

Did someone ask if he skimmed it?

EBEBRATT-Ed

Just another boiler that wasn't sized correctly

Get someone that has combustion testing equipment. Lower the gas pressure and test the combustion if it's good you won't have any soot issues. Most boilers can be down fired a little with no ill effects.

That won't eliminate the short cycling but will reduce it and give you longer smoother cycles

ecullina

Thanks

Yes it has been drained a couple of times but now the water is clear

Jamie Hall

Not drained -- skimmed. There's a difference.

Bronxtech

Also check the manual, hartford Loop pipe is very long to my eye, supposed to be a short nipple.