Steam Pressure Running Too High

mike212

This is my first heating season with a home that has steam heat. My one pipe steam system seems to be running too long, allowing pressure to get higher than desired. If the system has just been turned on, so that there is a lot of heating needed to reach the desired thermostat temperature setting, the system may run for an hour before the pressuretrol kicks in and rests the boiler to let the pressure drop. Those rests are pretty short, usually around 3 minutes.

At the recommendation of some others @nicholas bonham-carter and @Fred , I installed a wika 0-3 psi gauge. I've linked to some pictures of the new 0-3 psi gauge, the old 0-30 gauge, the pressuretrol and the pigtail.

I did not remove and clean out the pigtail as I was concerned I would not get the pressuretrol back on properly. Based on the pressure readings though I don't think the pigtail is clogged.

The 0-3 gauge ends up going beyond 3 for several minutes before the system ends up briefly turning off. Since that gauge doesn't read beyond 3 I'm not sure what the actual pressure was at that time. The picture I attached is not the most extreme reading, its just added to show what the setup looks like. The high pressure gauge gets up the 3-4 psi level but I'm not sure that is accurate since it doesn't always seem to be responsive and is pegged at 0 even when the 0-3 gauge reads 2.

Images:
http://addsnaps.com/i/tKeNzoz
http://addsnaps.com/i/MRxxhnj
http://addsnaps.com/i/Q6XbFTw

The pressuretrol is set to the lowest settings of 0.5 and 1.0 differential on the inside dial.

Any tests you recommend to figure out if I need to new pressuretrol or something else?

Also, I attached a picture of my pressure relief valve (http://addsnaps.com/i/5DYFPan). It is attached to the boiler on one side but nothing on the other side. Is that the proper setup?

ChrisJ

The pressure relief is installed fine, however, it needs a length of pipe running down to a few inches of the floor for safety.

Regarding your pressure issues and long run times, what vents are on all of your radiators? Can you take some pictures for us? How about main vents?

mike212

I have searched the house and can only find one main vent. The main vent wasn't closing fully and was emitting wet steam so I replaced it with a Bigmouth vent. That main has been working well now.

The main piping extends in the other direction as well into a crawl space, where it splits in several directions into at least 4 radiators the furthest around 25 feet away. There are probably more split offs beyond that but that is all I can follow through the crawlspace without ripping open walls to the top floor.

In that crawlspace piping there is no main vent and there is no cap or anything else that looks like it once had a main vent, at least as far as I can tell.

Once steam is produced by the boiler, it seems to spread through the crawlspace piping rather quick. I will re-test and write down the timings to feel heat in the pipes at various distances if that will help troubleshooting.

Many of the radiators do seem to take a long time to fill up with steam. From the time the steam enters the start of the radiator to the time it fills up can take > 30 minutes. Those two worst offending radiators have C sized maid o mist air vents. I have replaced some malfunctioning maid o mist vents with gortons vents of the same size. I will take an inventory of all the vents and and pictures and report back with everything.

Fred

How much are you trying to raise the house temperature? Many boilers are over-sized and it is not unusual for them to build pressure and short cycle when they run for an hour or more. Set the thermostat at a temperature that's comfortable for you and leave it there. I am also concerned that you are building 3 or more pounds of pressure when the a properly functioning Pressuretrol should shut the boiler down at somewhere between 1.5 and 2 PSI. It obviously works enough to shut the boiler off but at a higher than desired pressure. They can be re-calibrated. Here is the Procedure to do so and keep in mind the Pressuretrol is a safety control. It should not be the control that operates the boiler. That is the job of the thermostat.
Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with). You may need to play with it to get it exactly where you want cut out to be.

Jamie Hall

The pressure is a concern. Since the pressuretrol and the gauge are on the same pigtail, the pigtail would not seem to be the problem. And it would appear that the pressuretrol is sensing pressure, just not turning the system off when it should -- based on your settings on the pressuretrol, it should turn the boiler off at 1.5 psi.

The pressuretrol may need calibration, or it may be defective -- or it may just be partly clogged.

The fact that the boiler runs for a while, and eventually shuts off on pressure simply indicates that the boiler is bigger than it needs to be for your system.

mike212

Fred said:

How much are you trying to raise the house temperature?

This morning temperature in the house was 65. We set the thermostat to change to 68 at 6am so the boiler started. It took around 1 hour 20 minutes to reach 68.

It's been cold outside at night, but everyone in the house likes sleeping at a cooler temperature and warmer in the house during the day so we've let the house temp fall at night. Since I'm not confident in the pressure handling of the system - even before I installed that new gauge, I have typically only tried to raise the house temperature no more than 2 degrees at a time (two degrees on the thermostat results in a 2 to 3 degree increase in temperature since it sometimes overshoots). Today I did 3 degrees since I wanted to observe the pressure and see if the pressuretrol would kick in if the pressure kept increasing.

Hopefully the recalibration you recommended will help get the pressuretrol took cut it off earlier. I have some homework to do, will report back either way once I give it a try and have the opportunity to do some testing.

Jamie Hall

That setback and time scale is just about right.

ChrisJ

I've go for a new 0 - 4 PSI Vaporstat and a TRV in the bedrooms to keep the bedrooms cool.

Run the house at one temp, and the bedrooms will stay a cooler temp set by the TRVs. Plus, the bathrooms stay warm which is nice. Yes, I'm spoiled.

I keep the house 72F 24/7 but my bedrooms stay 64-66F.

mike212

@Fred , I'm having difficulty getting the 0.05 hex to turn. Here is an image of what I'm working with http://addsnaps.com/i/zoKWKFJ

You mentioned that it would be tight, but the 0.05 hex key is so thin that it just bends and doesn't exert enough force to unstick the hex head.

It appears there is something around the hex head that is holding it in place. Should I try scraping away that black stuff?

Thanks.

Fred

Yes, there is lock tight or some other glue on there. If you can scrap it off, it will help. The allen wrench is so thin that it will twist but it usually does turn that screw. If you have a hardened allen wrench, that will be less likely to twist. Keep trying, I haven't had one of those allen wrenches actually break on that screw yet.

Fred

Hatterasguy said:

Fred said:

If you have a hardened allen wrench, that will be less likely to twist. Keep trying, I haven't had one of those allen wrenches actually break on that screw yet.

I do not believe you can purchase an allen key that is not hardened. It could never apply sufficient force to meet the torque specification of the fastener.

I thought if it was hardened it would snap ??? I have a couple that look like candy canes. Never broke though.

SWEI

Alloys, tempering, and hardening have complex interactions.

mike212

@Hatterasguy I used some heat ... protected the plastic with a tripple layer of heavy duty aluminum foil and then used a butane torch on the lowest setting for 4 seconds.

I also got a hex screwdriver instead of the key because it's easier to turn. Got it loose!

@Fred so in turning the screwdriver I had to put quite a bit into the turn and ended up tightening (turning clockwise) quite a bit - way more than the recommended amount.

Tightening brings the diagphram further from the bottom while loosening brings it closer to the bottom. Be I messed with it I think it was near but not at the top, just a little bit of screw showing. My though is to position it there and the run it and adjust based on the pressure.

Two questions . .

1) turning screw clockwise and bringing diaphragm further from the bottom will reduce cut out pressure?

2) can I adjust screw while boiler is running and power is on or do i need to turn off boiler and kill circuit before turning screw? Obviously turning screw while pressure is around 1.5 until it cuts out will get me there quicker but I'm not sure that is safe.

Almost there!

BobC

Adjusting it while it's running is fine. If that pressuretrol is breaking a 120v line just make sure you don't get across it or you'll do the dance.

Bob

Fred

@mike212 , You should be Ok with it running, just be careful not to short anything. I like to set the thermostat high, let the boiler run, when it gets above the pressure you want, flip the power switch, make an adjustment, turn the power back on and let it run again to see how close you are, repeat if necessary. You'll get there.

mike212

Followed those instructions this morning, turning off power and breaker, adjusting and turning it all back on. Was quick to find the correct levels. Now it cuts in at 0.6 and cuts out at 1.9.

One question though, it take around 30 minutes to get the pressure to 1.9 the first time but the timings are very quick....

hits 1.9, turns off for 2 to 2.5 minutes...
hits 0.6, turn on for 2 to 2.5 minutes...
hits 1.9, turns off for 2 to 2.5 minutes....etc.

Is that too fast to go from 0.6 to 1.9?

Jamie Hall

Well, yes and no. Not that there is much you can do about it. The time to raise the pressure is related to the output of the boiler in relation to the size of the system. That short a time suggests to me that your boiler is somewhat more oversized than it needs to be -- but for the moment, it's there and it works. Is there a loss in efficiency? Yes, but it's not that great -- you could get the same loss by just misadjusting the burner slightly. I don't recall whether you mentioned that you are using oil or gas, but in many cases it is possible to slightly downfire the boiler. The time for the pressure drop is related to the size of the system only, not the boiler.

mike212

I'm using oil for fuel. I'll do some reading about down-firing the boiler to see if its something I want to attempt. If the boiler were sized properly, approximately how long should it take to go from 0.6 to 1.9 PSI?

KC_Jones

If the boiler is sized properly you will most likely never see those pressures and possibly never trip on pressure, unless you are doing a long recovery or running for a long time at design temperature.

ChrisJ

When my boiler was sized "properly" according to most, it took 1 hour and 20 minutes (80 minutes) to hit 1.5 PSI.

Now, it will probably never even come close to that no matter how long it runs.


If your boiler is oil fired, I would get someone in there with a combustion analyzer and see how low they can get it.

Fred

@mike212 , The magic number, in your case is the 3 minutes it took for the pressure to build enough pressure to cause the Pressuretrol to trip. Remember, you set the thermostat high to allow you to re-calibrate the Pressuretrol. I would say, at least 80% of the time, the boiler will not run for 30 minutes on a normal heating cycle time before the Tstat is satisfied and the 2 minute short cycles will not occur. That is the very reason we suggest not doing set-backs when it is known that the boiler is over-sized. Keep the tstat set at a comfortable temp and the heating cycles will remain under 30 minutes, except perhaps on design days when you might hit a few short cycles. Those days won't be that often and remember, increasing the cut-out pressure on the Pressuretrol won't change the short cycling times by more than a few seconds so don't raise the Cut-out pressure. Allowing the system pressure to increase also means you are slowing the steam flow down. Seems counter intuitive but it is true.
Set the tstat back to a normal temp and watch the boiler. It will do it's job.