Correct Max pressure for a steam boiler?

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Old 11-17-10, 08:43 AM
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Correct Max pressure for a steam boiler?

My system is a Weil Mclain Oil fired single pipe steam system with a riello Burner.

My pressure control is set to 2psi min and an 3 psi additive differential for a max of 5psi. Yet I was in the basement the other day and noticed my pressure gauge at 20 psi and the unit fired on. This seems odd to me. I looked at the schematic from my system and the pressure control is in line with the Ac 120volt supply to my boiler so this shouldn’t happen.

I think that I may either have a bad Gauge, pressure control or I don’t understand this as well as I thought.
 
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Old 11-17-10, 02:40 PM
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I think even 5 PSI is too much, 20 is a crazy lot!

How did you arrive at the settings you are currently using ? 2 + 3 ?

There could be a combination of things going on...

My first suggestion is to "NEVER TRUST A BOILER GAUGE!" You should verify that before you go running around trying to find another problem. It could be ALL that is wrong, or maybe not.

What is the model number of the boiler, and which model Pressurtrol is on there?
 
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Old 11-17-10, 04:25 PM
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ALL residential steam boilers have a Maximum Allowable Working Pressure (MAWP) of 15 psi. Either you read the gauge incorrectly or the gauge is nothing but a paperweight attached to the boiler.

Most residential steam heat systems work well with less than 2 psi and some work well with 1/2 psi...or at least as well as a residential steam system can.
 
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Old 11-17-10, 04:29 PM
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The settings were there from my oil company when they replaced the boiler several years ago. What would you suggest as better numbers?

The Pressuretrol is a Honeywell PA404A. Ant the boiler is a Gold series from Wiel Mclain A/B SGO-4.

I guess i will buy a new pressure gauge this weekend.

Thanks for the reply.
 
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Old 11-17-10, 04:35 PM
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The gauge is 0-30 with markings for each pound and has numbers at intervals of 5 and PSI in caps on center. So i guess its a paperweight.
 
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Old 11-17-10, 04:40 PM
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I would start with Furd's pressure recommendations, cut in at 0.5 PSI and add 2 PSI differential... heck, they heat the Empire State building with 9 PSI!

Yes, please check the gauge first!

Might wanna take a look that the pigtail (aka 'siphon') isn't plugged up too...

Do you do all the good stuff like blow down on a regular basis, etc?
 
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Old 11-17-10, 04:47 PM
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Not sure what you mean by blow down, if you are talking opening the low water cutoff to clean any sediment then the answer is yes.
 
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Old 11-17-10, 04:55 PM
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Just checked the boiler gauge is at 13psi, adjusted to the .5 psi cut in and 2 PSI differential. Just to make sure i am doing the correct thing the Pressuretrol is adjustable from .5-9psi and will now be using the minimum setting. Adjusted the settings cranked up my thermostat and the boiler fired up so the gauge must be garbage.
 
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Old 11-17-10, 05:24 PM
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My system was also set to cut out at 5 psi. I never found any specifications in any of the manuals, but the previous homeowner always had the system professionally serviced, so I assumed it was set correctly. Based on what I've learned from reading this forum and the articles on the Technical Menu, I'm going to try running at a lower pressure, especially since I've been dealing with some leaking issues.

A few years ago I also discovered my system pressure was too high when I went to blow down the low water cutoff. It was almost up to 10 psi and still heating, so I turned the adjustment screw on the pressuretrol until it shut off. Then I found it wouldn't cut back in. I wasn't sure what was wrong, but I took everything apart and cleaned and lubed all the moving parts that might stick. When that didn't fix it, I suspected the siphon loop might be clogged. I didn't have a new one, but I knocked it around and jammed a wire brush into each end as far as I could and a lot of crud came out, and I could blow air through it, so I put it back together, and it's worked great ever since.

In addition to checking all of the above, if your pressuretrol uses a mercury switch, make sure it's level. If the siphon tube is bent, that will throw off the setting. The loop also has to be aligned with the pivot point of the the mercury switch, because the loop expands under pressure, and that can affect the level.

Your gauge might not be lying to you. If it goes to zero when the system cools down, it's probably working. If it only goes down to 15, it's not calibrated properly. If it doesn't move at all, you need to replace it, but you can often get a somewhat accurate reading by gently tapping on the housing to free up the mechanism.

But frankly, I wouldn't want to get that close to a steam boiler whose gauge read 20 psi. Steam boilers are dangerous even under normal operating parameters, and 20 psi is well outside of normal. If you can't get it fixed immediately you can keep your house warm temporarily by running the burner until the pressure reaches 5 psi and shutting it down manually, either with the thermostat or the pressuretrol adjustment screw, but I wouldn't want to run it without keeping an eye on it.
 
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Old 11-17-10, 05:33 PM
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Yes. Blowing down means opening the low water cutoff valve while the system is operating to expel sediment from the low water cutoff and to verify that it works. The float switch should shut off the burner when the valve is opened and turn it on again when it's closed, assuming your water level is still adequate. You should also see the water level in the sight glass drop when the valve is opened and rise again when it's closed.
 
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Old 11-17-10, 05:37 PM
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If you EVER see more than 15 psi on the pressure gauge you need to cut the power to the burner and let that bad boy cool down. Residential steam boilers are limited to a MAXIMUM pressure of 15 psi and at that point the safety valve should open. If the safety valve doesn't open then it MUST be replaced.

Since residential steam boilers run at such low pressures the safety valve never operates on its own and even hand testing of the safety valve is limited by the fact that a safety valve should not be hand tested with less than 2/3 of its set pressure. This would mean that a residential steam boiler should have a minimum of 10 psi on it before hand testing the safety valve. In most cases (probably 99.9% of all residential steam systems) this is impractical so the best insurance is to REPLACE the safety valve every three to five years.

Did I mention I detest residential steam heating systems?
 
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Old 11-17-10, 05:56 PM
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Being new to the forum i didn't see the Technical Menu, just did some light reading over there. Checked my piping as per diagrams there and that looks good not that it has anything to due with my current issue but figured i would check it anyway. So far the boiler hasn't cut on in the last half hour with the new settings (event tough i have thermostat adjusted high for boiler demand). The gauge is coming down slowly. I do know that i have seen the gauge all the way at zero.
 
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Old 11-17-10, 06:03 PM
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The Sipon Loop on my pressure troll is just a cooper coil is this an accepted practice?
 
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Old 11-17-10, 06:09 PM
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Take a pic...

of the siphon loop... free account at Image hosting, free photo sharing & video sharing at Photobucket , upload pics there, place link here (or link to the image directly)

You mean it's just a hand formed loop of soft copper tubing?

Is your gauge on the same end of the loop as the pressuretrol? If it's NOT, definitely suspect that loop is clogged, and the pressure is REAL...

In fact, a more general statement could be made, always err on the side of safety and assume that the gauge is correct, UNTIL PROVEN OTHERWISE.

Good info Bruno, thanks! but I wouldn't assume a gauge is accurate just because it does go to zero. They will often still zero, but read higher upscale.
 
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Old 11-17-10, 06:36 PM
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Here's the link to some pictures. and Yes i meant a hand formed loop of copper tubing.

Pictures by 944t - Photobucket
 
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Old 11-17-10, 06:45 PM
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That's a proper siphon... machine made, etc... but, if that siphon is clogged, it won't sense the pressure in the boiler. My money is on a clogged siphon tube... the gauge on the boiler in this case, BELIEVE IT for now.

Can you see the PSI rating tag on the relief valve?

I wanna see the Porsche...
 
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Old 11-17-10, 06:48 PM
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BTW, I should think that you might notice some fuel savings by running the pressure lower.
 
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Old 11-17-10, 06:51 PM
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It says 15PSI. The pressure is still dropping and no fire yet even though demand is called for. tomorrow when its cold( i turn heat really low at night) can i just remove pressure troll and use a wire on the copper tube then suck out the debris with my wet vac?
 
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Old 11-17-10, 06:56 PM
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I might have seen some savings, but my hot water coil aquastat was set to 130 degrees which i learned is too low so i have to turn that up which will keep the boiler hotter than i used to so i think the savings will be lost. I wasn't getting enough hot water so i call Weil Mclain and they recommended a company to clean the coils from Nj Franks Coil Cleaning but Frank was a nice guy he explained that the aquastat was way to low. I also read the owners manual from Weil and it states that the specs for the coil are based on 200 degree water temp.
 
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Old 11-17-10, 07:12 PM
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I'm hoping that one of our experienced steam heads can enlighten me here...

Looking at the manual for the SGO, and comparing to Edward's pics, it is clear that Edward's system has some 'fitting' differences from those shown in the manual.

http://www.weil-mclain.com/en/multim...manual.pdf.pdf

Mostly in the location of the gauge glass. The tapping that the gauge is in on Ed's system is called out for the gauge glass... the lower gauge glass port is plugged.

OK, the manual also shows the pressure gauge mounting on the control end of the siphon. (which is where I'm used to seeing them in my limited steam experience).

Now, let's say the siphon gets clogged (as I suspect this one is)... with the gauge mounted at the control, how could you ever be sure of the pressure in the BOILER? Wouldn't it make a whole heckuva lotta sense to have a gauge at BOTH places? at the Pressuretrol AND on the boiler? If the gauge on Ed's system WAS at the pressuretrol end of the siphon, he might never know that the tube was clogged...
 
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Old 11-17-10, 07:21 PM
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OK, there's still the 'unknowns' here... the gauge was reading 20, but the relief valve is a 15. One or BOTH of those items are toast. For safety sake I would replace the relief valve.

How on earth is one supposed to remove that siphon tube the way it's mounted?

Shop-vac, maybe... compressed air? maybe... I don't know that you'll get a wire in there though... maybe a small sewer snake? flush it with a garden hose?

What did Frank suggest you set the HW aquastat to?
 
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Old 11-17-10, 08:26 PM
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Has it been determined that the safety (not relief) valve is indeed a steam model and set for 15 psi?

The mounting of the gauge glass is okay, it does give a more limited view but it still has the minimum water level in view. The location of the pressure gauge is absolutely wrong and I guarantee that gauge is toast. The purpose of the "siphon" is to ensure that steam never reaches the internal parts of the pressure gauge or pressuretrol (only one l and a single word.) If that pressuretrol was a mercury switch model them the orientation of the siphon would be 90 degrees off but with the microswitch models it is not important. It is obvious to me that the siphon was piped up before the conduits and service switch were attached.

You need to add a tee under the pressuretrol and install a new gauge at that position and then plug the port where the gauge is now located. I think I would just go buy a new siphon rather than trying to clean the one you have.
 
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Old 11-17-10, 08:40 PM
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I would just go buy a new siphon rather than trying to clean the one you have.
And then to get the old one off, cut it with a hacksaw, then spin out the elbow, and the new one would be oriented such that the sticks out from the boiler, correct?

Since the relief valve did not open, and Furd is confident that the gauge is NFG, it is possible that there wasn't really 20 PSI in the boiler...

Sounds like a plan to me...
 
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Old 11-17-10, 08:53 PM
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Yep, cut off the old siphon and then remove the elbow. Also remove the nipple from the boiler tapping and replace with a longer nipple. Instead of using an elbow, use a tee (or even better, a cross) and plug the unused opening(s). This allows you to remove the plugs and run a rod through the straight passages to make certain they are clear. Use a union between the pressuretrol and the upper tee to allow removal of the pressuretrol without having to undo the wiring.

I haven't looked at the manual (maybe later) but there are several things that really need to be done to steam boilers EVERY YEAR before the heating season. Maybe I'll write something up.
 
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Old 11-18-10, 04:19 AM
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Originally Posted by NJ Trooper View Post
Now, let's say the siphon gets clogged (as I suspect this one is)... with the gauge mounted at the control, how could you ever be sure of the pressure in the BOILER? Wouldn't it make a whole heckuva lotta sense to have a gauge at BOTH places? at the Pressuretrol AND on the boiler? If the gauge on Ed's system WAS at the pressuretrol end of the siphon, he might never know that the tube was clogged...
It absolutely would. I think I might even add that to my list of things to do when I overhaul my system in the spring.

With a single gauge I think it makes more sense to have a gauge tapped directly into the boiler so it would tell you what the pressure really is, not just what the pressuretrol sees, but having one in both places would tell you immediately if the siphon tube was clogged or if there was a mechanical problem with the pressuretrol itself. Not only that, but two gauges is like getting a second opinion. If they don't agree you can always swap them and see if there's a real pressure difference or if one of the gauges is off.
 
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Old 11-18-10, 04:25 AM
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Thanks for all the info, this morning i got up early and turned the boiler back on. With the unit firing and up to 10psi on the gauge air wasn't escaping from radiators, so I kept going based on that I think the gauge is toast. As it went higher around 15 I was finally getting air venting, and all the radiators are now hot.

The pressuretrol is a micro switch.

Any recommendations on gauge and pressuretrol? Also is the such a thing as a Programmable aqua-stat so i can set it lower when showers aren't going to be happening? This way i may be able to save oil in the summer. Also what type of thread sealent is good for it, teflon tape?
 
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Old 11-18-10, 04:35 AM
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Another location for the siphon tube

You could also mount the new siphon tube on top of the low water cutoff. That's when mine is. You'd just remove the plug and put it where the elbow holding the siphon tube is now, then screw the siphon tube into the top of the low water cutoff. You might not have enough cable to put the pressuretrol all the way out there though. I've never seen a low water cutoff stuck out so far from the boiler like that before.

Note that the unit in the manual NJ Trooper posted doesn't even have a low water cutoff! I'm guessing this probably accounts for some of the differences in where things are located.

Correction: The unit in the picture has a probe-type low water cutoff. I've never seen one of those before. The drawings on page 11 show recommended locations for both types.
 
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Old 11-18-10, 05:45 AM
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I think that one important point that Furd indirectly mentioned in one of his posts is that any gauge on a steam system must be mounted on a siphon tube. I believe the reason is that the steam itself must not be allowed to reach the gauge, as it will quickly destroy it.

If redundancy were preferred, and it would seem to make sense based on the fact that the tubes do clog occasionally, then perhaps two gauges mounted on separate siphon tubes would be in order.

I'm looking now for an application note that explains the why/why not's of gauges on steam systems, but haven't found one yet.
 
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Old 11-18-10, 05:12 PM
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My pressure gauge is located in approximately the same place on my boiler, and it's lasted at least ten years. The unusual thing about it is that it goes from 30 psi down to 30 in of vacuum, so zero isn't at the bottom of the scale; it's at about 10 o'clock. Pictures in some of the the manuals and catalogs I've found online show gauges in this same location, and the needle is pointing right about where zero would be, so I suspect this is the original gauge. If so, it's lasted at least 23 years with no siphon, outlasting a couple of pressuretrols and low water cutoffs.
 
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Old 11-18-10, 06:01 PM
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There are some boilers (Pennsotti is one, I think) that have an internal chamber or pipe that holds water to keep the steam from the gauge. There are also some gauges that have an internal siphon. If the gauge is located below the waterline it might be okay but is still not the preferred method.
 
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Old 11-18-10, 06:38 PM
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Looking recently at app notes and specs on all types of different gauges, I find that they are as I expected 'all over the place'. There are as Furd said types that are suitable for steam directly (internal siphon). The thing that I noticed most was the 'temperature rating' of the gauges... I don't think I saw a single 'general purpose' gauge that had a temp rating over 200° or there abouts... the part that is on Edward's boiler looks like a 'run of the mill general purpose' variety from US Gauge...

That said, there were a number that I saw that were called 'industrial' gauges that had ratings up to 500° and even a bit higher.

So, perhaps the bottom line here is that the gauge needs to be specified for it's application. Without a doubt, a gauge from HD or Lowes would probably fail almost 'instantly' if fed with live steam. Bruno, chances are the one on your boiler is rated for the purpose... and I'll betcha big $$$ now a days...
 
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Old 11-19-10, 08:18 PM
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Originally Posted by Furd View Post
There are some boilers (Pennsotti is one, I think) that have an internal chamber or pipe that holds water to keep the steam from the gauge. There are also some gauges that have an internal siphon. If the gauge is located below the waterline it might be okay but is still not the preferred method.
My gauge does say it has an internal siphon.
 
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Old 11-19-10, 08:26 PM
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Originally Posted by NJ Trooper View Post
the part that is on Edward's boiler looks like a 'run of the mill general purpose' variety from US Gauge...

Bruno, chances are the one on your boiler is rated for the purpose... and I'll betcha big $$$ now a days...
Mine is a US Gauge. It looks like a pretty good gauge. I think it might be a good idea to try to determine what kind of gauge someone has, and what condition it's in, before advising them to replace it. If I'd tossed mine and replaced it with a brand new Home Depot special, I'd be an unhappy camper right now.
 
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Old 11-19-10, 09:08 PM
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I think it might be a good idea to try to determine what kind of gauge someone has, and what condition it's in, before advising them to replace it.
Isn't that what we're doing? I quickly scanned back and didn't see where anyone suggested disposing of a gauge until the accuracy was verified (or not), and it was proven to be appropriate for the application.

I looked very closely at the picture of Edward's gauge and I did not see any indication that it had an internal siphon. It looked like a standard gauge. So where do you see that we advised anyone improperly?

The bottom line here is the advice given to Edward was to VERIFY HIS GAUGE, and to check if the siphon is clogged. He also got advice on how to replace the siphon which his installers made irreplaceable by it's location and proximity to the boiler and the electrical controls.

Edward, I would not use teflon tape on the connections to a pressure sensing device. If you feel the need to use some sealant, use a good quality pipe dope, and don't put any on the first two/three threads.

I don't see any need to replace the pressuretrol unless you determine first that it's defective.
 
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Old 11-20-10, 04:08 PM
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Good news I was never running high pressures the old gauge was at fault. Now I have a no name made in china gauge. Anyone know of a good gauge? I bought the only gauge my local plumbing supply had in the 0-15psi range and I couldn't find any at Home Depot. Does Lowes carry any good ones?
 
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Old 11-20-10, 04:34 PM
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Forget the big box stores...

Any gauge that does not have an internal siphon needs to be mounted on an external one. You should be able to use pretty much any decent quality gauge if it's mounted on the siphon.

Is there a local heating supply near you? Decent gauges can sometimes be found at pool supply houses also.

You could also set up a tee on the top of your existing siphon and mount the gauge there.

Still not a bad idea to check that the existing siphon is clear.
 
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Old 11-20-10, 10:58 PM
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Pressure gauges should have a full-scale reading about 1-1/2 to 2 times the maximum expected pressure for best resolution. Using a 0-30 psi gauge on a boiler that is going to have a maximum pressure of 2 psi means the gauge will barely get off the pin. For pressures in the 0.5 to 5 psi range I prefer a diaphragm-type gauge rather than the more common bourdon tube gauge. Of course they aren't cheap. Here are a couple that I would use.

Tel-Tru

Wika

Of course being the nut I am I would probably toss both the gauge and the pressuretrol and instead use a platinum RTD (Resistance Temperature Device) to a digital display/controller calibrated to convert the temperature reading to pressure, maybe 300 to 500 bucks.
 
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Old 11-21-10, 06:38 AM
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Looking at the spec sheets, I note that the Wika gauge is spec'd for a maximum of 140°, gaseous or dry media.

Furd, is the siphon adequate protection to keep the gauge gaseous or dry? No chance that condensate will find it's way into the gauge? ( I assume that's the purpose of the siphon, that, and temperature protection )
 
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Old 11-21-10, 06:45 PM
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Forgot to mention I uploaded a new pic of the install on photobucket. I think i will keep the cheap gauge mounted in the pic. I will leave that on where it is and buy a good one to t with the pressuretroll. Going back and looking at the thread i see i missed some questions. Trooper Just saw the hint for a car pic. Also you asked
What did Frank suggest you set the HW aquastat to? he said 180. If you llok in a weil mclain manual it says hot water coil specs are at 200, So i was really low at 130.

Pictures by 944t - Photobucket

Now for the next phase of optimizing my system, I am going to work on my vents and leaky valves at the radiators, and insulate some of the pipes in the basement.
 
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Old 11-21-10, 08:28 PM
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Nice lookin ride Edward! Great scenery too! Bet you find some great roads to cruise...

That gauge should be OK up there away from the steam and outta the heat.

he said 180. If you llok in a weil mclain manual it says hot water coil specs are at 200, So i was really low at 130.
Thing you gotta be really careful of is scalding injuries... The potential for EXTREMELY hot bursts of water is very real. I see some kind of mixing valve on the domestic piping, but can't really tell what it is... the valve that goes between the in/out pipes on the coil... I always recommend a thermostat mixing valve, and it's something that you should consider in order to limit the domestic hot water to something safe... say 125°

Next, you must understand that by pushing the temp that high, you will absolutely be burning more fuel. So, it's in your best interest to run it as low as possible and still have adequate hot water supply to the home. Turn it down a little at a time to the lowest possible setting consistent with adequate HW. But yeah, 130 was too low...

If your plans are to stay in the home for a number of years, you probably ought to strongly consider a more efficient way of producing your domestic hot. A kettle on a wood stove is only marginally less efficient.

Early on you mentioned this, and I don't see where it got talked about...

Also is the such a thing as a Programmable aqua-stat so i can set it lower when showers aren't going to be happening? This way i may be able to save oil in the summer.
It wouldn't require a programmable aquastat. You could do this with a cheap programmable THERMOSTAT.

First though you want to verify that the existing aquastat is LOW VOLTAGE. (I'm sure it is, but you do need to check).

Here's how to do this... Wire the thermostat in SERIES with the wires from the DHW aquastat. Program the thermostat for the times when you want to use hot water. Here's the twicky part... hope I can explain this: Program the 'AWAY' or 'SLEEP' times on the thermostat for the LOWEST POSSIBLE TEMP SETTING on the THERMOSTAT (NOT the aquastat, leave that where ever you find is the appropriate setting), and program the 'HOME' or 'AWAKE' settings for the HIGHEST POSSIBLE TEMP SETTING.

The idea here is that these temperatures (typically 50-ish and 90-ish) will NEVER be seen by the thermostat, and it will act as a simple TIMER.

Example, you want hot water from say 4 PM to 11 PM. You program this time period to 90°. At 4PM the thermostat will close and ENABLE the aquastat on the boiler to raise it's temp to setpoint so you can have hot water. Since the thermostat is not in control of the room temp, it will never see 90 and so will continue to call. On the other side, program for 50 at 11 PM till say an hour before you wake up... At 11 PM, the thermostat will OPEN, and DISABLE the DHW control on the boiler. The room will never cool to 50, so it will stay open...

It's a cheap and easy, quick and dirty way to put a programmable timer on a low voltage control circuit. Just make sure to mount the thermostat somewhere that will never see the two temperature extremes. If you mount it somewhere in the living area, you can be almost certain of that, and you will also have easy access to push the 'HOLD' button to over-ride the program if your schedule changes for a day or whatever...
 
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