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Couple more observations about Pressure Relief Valves

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Eric Johnson, Dec 1, 2005.

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  1. Eric Johnson

    Eric Johnson Mod Emeritus

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    We touched on this in another thread, but I thought I'd make a couple more points about pressure relief valves on both domestic hot water heaters and boilers.

    Again, both use PRVs and they look identical to the untrained eye, especially when they're installed. However, PRVs for boilers open at 30 psi while those on domestic hot water heaters lift at a higher pressure. Elkimmeg says 50 psi, which sounds right to me. If you put a 30 psi PRV on a water heater, it won't work at all because the valve will lift and stay open once filled with tap water under normal, household pressure.

    Put a hot water heater PRV on a boiler, however, and your boiler could reach a dangerous (i.e., explosive) pressure before the relief valve blows. So it's important to know what you're doing and to read the tags, which describe the appropriate application and pressure pre-set.

    You should also periodically lift the lever on all your PRVs to make sure that 1.) the valve can open and 2.) water comes out when it does. PRVs can get scaled and/or gunked up or simply fail, at which point they need to be replaced. When in doubt, swap it out. In the case of boilers, yours may well contain a mixture of glycol and water. You will know this if it has a red or green or yellow color and feels a little more viscous than water. Heating system glycol (antifreeze) is expensive, so try not to waste more than necessary. Also, if you're going to let water out of the system, make sure you have a domestic water feed hooked up (and activated) that will replace it, or find another way to replenish what's been lost.

    The problem with manually opening a PRV is that some of that same gunk or scale can get caught on the valve seat, allowing the valve to leak after you let go of the lever to close it back up. There's not much you can do about this other than open the valve again wide and hope whatever is causing the problem flushes out. Sometimes I bang on them lightly, partly out of frustration and partly in an attempt to dislodge the offending crud. Usually, I give up eventually and hope that the valve stops leaking on its own, and usually it does. Stick a bucket or cup or other container under the drain pipe to catch the water.

    Oh yes, all PRVs should be piped down to near the floor (usually a piece of 3/4-inch copper soldered to a threaded adapter and screwed into the valve's 3/4-inch drain outlet. This reduces the chances of someone being scalded by steam or hot water if they happen to be standing near the valve when it blows.

    Finally, I like to know what my valves have been up to. If you're running a little hot and the valve opens from time to time, that's something you should know. But if you let the water or glycol drain out onto the floor, you may not notice it. That's why I always keep a can or bucket or plastic cup under the drain pipes of my valves. If they contain fluid, you know something's up. It looks a little tacky, I know, but it's a fashion compromise I'm willing to make for the sake of safety.

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  2. elkimmeg

    elkimmeg Guest

    Great informative post 100%. On on the relief valve extentions required by code: no less than one foot from the floor
    for the very reasons you mentioned. Another item on my final Mechanical check list Aslo read my prior post and know where your pressure gage should be reading. If you pressure has exceeded 20 psi then you variable fill valve is failing. if it continues to rise your PRV at 30 psi should blow. Another way to check is to turn off your water supply. Its ok to run a closed system a day or so if no more pressure rise occures, then it is definitely your fill valve. Again sediment minerals crud can cause these valves to fail they have to be peridiocally replaced. Again this is for discussion. If you do not know your way around a boiler do not start experimenting
  3. Eric Johnson

    Eric Johnson Mod Emeritus

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    Yes, if the fill valve is leaking, your system pressure will rise and eventually blow the relief valve if the leak is big enough. Another cause of head-scratching pressure rises is tankless domestic water heating coils and other heat exchangers. Since, in the case of the coil, you're running higher-pressure domestic water through a copper loop in the lower-pressure boiler vessel, any leak that develops there will force tap water into the boiler and jack the pressure up accordingly. Again, depending on the size of the leak, it could be enough to lift the PRV on your boiler.

    I should also add, since I brought up glycol in the original post, that you should never try to use automotive anti-freeze in a hydronic heating system ESPECIALLY IF ITS CONNECTED TO YOUR DOMESTIC WATER THROUGH A FILL VALVE. If the valve leaks and the pressure in your house water drops, poisonous automative glycol will leak back into your domestic water and could very well poison your family. Heating system antifreeze, while more expensive, is non-toxic and therefore a safer bet. I still have a check valve between my boiler fill and the house water. If you're really paranoid, you can get a special check valve that will dump the boiler water/glycol mix on the floor before it will allow it back into the house.
  4. Corey

    Corey Minister of Fire

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    As my grandpappy used to say, " 'taint the pressure that gets ya...it's the temperature"

    I assume in the above commentary you are really talking about a "PTRV" or Pressure/Temperature Relief Valve? My water heater runs a valve that will vent at a pre-set pressure, or if the temp rises above ~210F. Actually had that happen in an old house when the thermostat broke and the burner stuck on. The pressure relief is actually a secondary back-up to the temperature dump part of the valve. The one thing worse than a pressure vessel explosion is a pressure vessel explosion that contains superheated water! I suspect domestic boilers are set up the same way?

    Corey
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    Corey,

    Yes on the first question. I tried to find a water heater relief valve once without the temp. set, and came up empty. Mine is set for 210 degrees and (surprisingly to me) 150 psi on the pressure side. My understanding is that the temp feature is mostly to protect anyone who might open a tap in the house from a really bad burn.

    I've never seen a boiler relief valve with a temp. feature, as indicated by a probe that goes from the valve and into the vessel. That might not be a bad idea, except that boilers can run up to 210 without too much trouble, and you don't want to blow the relief valve unless absolutely necessary, since if you are running glycol you don't want to blow it out of the system unless there's no alternative. Most conventional boilers, if they're set up correctly, have an aquastat set at, say, 200 degrees, that will cut the power to the burner if the setpoint is reached. With a solid fuel unit, you can do essentially the same thing with an aquastat that activates either a pump or a zone valve (useful in the event of a power failure) to dump the heat into one of the zones. Not a bad idea as an extra safety feature on a conventional boiler as well.
  6. Sundeep Arole

    Sundeep Arole New Member

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    I do have a question about my new boiler which just got installled last month. There are the P&T valves, and then also a mixing valve which tempers the DHW from the boilers tankless coil by mixing it back with cold. The temprature setting is okay at the sink, but at the shower there is a pressure balanced valve and so when it is all the way open, water is still lukewarm, at best. So I think the DHW temprature out of the boiler really needs to be higher.

    My question is this - Is this a homeowner adjustment, or am I better off just calling the oilmen? They say non-emergency stuff it is a while before they can come out. Meanwhile, I am stuck with having to shower in the office or the gym. On the valve there looks like a cover with some kind of allen screw lock, so I think there is some attempt made to ensure homeowner won't tamper with the setting.

    There are also two limit settings on the aquastat - I presume I should leave those alone too?
  7. Jfigliuolo

    Jfigliuolo New Member

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    I change my mixing valve settings... no problem.
  8. Eric Johnson

    Eric Johnson Mod Emeritus

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    I have a tempering valve that is adjustable by turning a knob on the top of the valve, so you should be able to crank up the DHW temp just by making an adjustment. Maybe they make some that are not adjustable, but I doubt it. That's kind of the whole point. Are you pulling your hot water right out of the coil or cycling it into a conventional hot water heater and then drawing your hot water when you need it from the tank? If you can do that, it works better, in my experience.

    If you can't raise the temp by adjusting the tempering valve, then your only alternative, it would seem, would be to run the boiler hotter. I've run wood-fired boilers as hot as 210 in an attempt to achieve a secondary burn, but you have to keep an eye on it if you're going to do that. My gas-fired unit peaks out at about 180.

    If the business that installed the boiler is too busy to come out and take a look, maybe they would be willing to give the information you need over the phone. Turning the aquastat to a higher setting is no big deal--just a turn of a screw slot in most cases. But you probably don't want to mess around with it without finding out what the recommended high temp is, if for no other reason than it's probably still under warranty.

    One more note about tempering valves: The cheap ones, like the one I have, simply mix cold water into the hot at the ratio you set with the adjustment knob, instead of automatically adjusting the flow to achieve the desired DHW temp. They assume more or less consistent temps on both sides. You're not going to get a consistent boiler water temp with most wood-fired units, which screws things up, although if you have a conventional boiler set to maintain system temp, it works pretty well. The other problem is that when you're not drawing hot water through the valve, the "cold" water waiting in the pipe to be mixed can warm up to room temp (hotter if it's near a heat source). As a result, you get a big burst of very hot water when you first open the tap, because you are temporarily mixing hot water with warm water, instead of hot water with cold water. If you want to spend a couple hundred bucks, you can get a true tempering valve that senses the temps and adjusts itself accordingly.
  9. elkimmeg

    elkimmeg Guest

    I know if you have a simmons shower valve there is an adjustment there. I have to look at mine first to advise you
    You also provbably have a restrictor on the head to conserve water some call it a wigit This too can act to adjust the spray to feel cooler allowing a finer spray more exposure to coolerair temps before it hits your body. First approach is to adjust the mixing valve at the shower. Again over time scale sediment can effect the prior settings. Couple of things to consider here. One your old boiler may have been set to 140 to 160 Anti scald codes it is now set to 120. But nobody adjusted your shower valve it is set to receive water at a higher temp mixing in with cold. If the water is not as hot then, less colder water should be mixed at the shower valve.
    At it old setting it is not adjusted for 120. Changing the burner setting you will be wasting energy and run the chance you kids could get burned using the fawcet closest to the boiler
  10. Rhone

    Rhone Minister of Fire

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    Well Hotflame, now you're in my realm... plumbing! They should tell people these things when you buy faucets and new showers and such, I never understood why they don't. A mixing valve is required first off, your boiler person had no choice but to install it and it also should be around 12" below the hot out of your boiler. What they don't tell you is when you buy replacement faucets and the like your house is either supposed to have all faucets, showers, and sinks everything with one handle operation and set your mixing valve to 140F OR all are supposed to be two seperate handles each controlling either the hot or cold and mixing valve set to 120F. The one handle valves WILL NOT work without mixing at least some hot/cold and that's your problem. You have the situation where your mixing valve is set to 120 and your shower must be a single faucet control and having to mix a little cold water in it for that valve to work causing only warm showers.

    Here's what you do. First off, your shower has an easily accessible screw that determines how far it can be turned to hot before stopping. Before mixing valves, that's how they prevented you from scolding yourself in showers. Take the handle off your shower and the nuts and make sure that screw isn't set to prevent you from turning your shower as high as it can go. For safety sake, shut the water in your house off first.

    If it is set so it doesn't interfere with how high you can turn your shower, or still isn't enough the next is to increase your mixing valve yourself (yes you can do it yourself) to somewhere around 140F. Then, when the water hits your shower it will mix in a little cold water and still be hot but the two handle faucets in your house you'll need to turn the cold on also as you can now scold yourself on them.

    The last step if you really want to make it work is to set your mixing valve to 140F and get a mixing valve for each of your faucets that have seperate hot & cold and adjust it so you don't scold yourself using only the hot on them. There are undersink mixing valves designed specifically to fix the issue of mixing the two different types of water controls in one house. That could be why they don't tell people their house should be all one type or the other, or replace all your faucets that have seperate hot & cold controls with single-handle designs so your house is all one type. Man those others beat me to the punch, they type fast.
  11. elkimmeg

    elkimmeg Guest

    Here is a tip: The boiler mixing valve for your domestic Hot water has adjustable settings some times number settings. These valve are prone to scale crud in the water and fail within a few years This tends to be an expensive repair. Your burner man loves, simple to do, you are glad to have Hot water and that will be $199. Want a permanent solution? Eliminate the mixing valve and install two common ball valves one to the cold water supply and one to the hot water leaving the boiler. Open each one the amount you are satisfied and forget it It will take some tweaking but you should never have to replace that hot water mixing valve again
  12. Eric Johnson

    Eric Johnson Mod Emeritus

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    That's a great idea, elk. Accomplishes exactly the same thing for about $10 and a little soldering.
  13. Sundeep Arole

    Sundeep Arole New Member

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    Wow this is just great - thank you Eric, Elk and Rhone. It turns out I have lucked out on the faucets, as all faucets in my house are single handle controls. The water is definately hot when I turn it all they way hot at the sink, but it could be a bit hotter. I do indeed have a Symmons valve, I removed the shower handle and there is indeed the set screw you are talking about. Unscrewed it out all the way, but shower is still lukewarm, though definately hotter than before. So I'll try the next suggestion - try to adjust the tempering valve setting to 140. Elk when you say anti scald code does that mean a plumbing inspector would fail my boiler if I changed the setting, or is it just a recommendation. I'd like to give this a try.

    On a side note, I called Symmons today to ask about their shower valve - what a awesome bunch of folks. The shower valve - this one came with the house, and maybe not all that new. Even though I didn't buy it myself originally, they were more than happy to answer my questions and tell me how to adjust the setting. They even are sending me a new stem free of charge as they said the valve can become lodged with sludge over time, and stem replacement might help the problem too. Also, there is apparently a special kind of stem which works better for tankless coils. Anyway, they treated me very well, these folks get my vote, and they deserve all the business they can get.
  14. elkimmeg

    elkimmeg Guest

    My plumbing inspector actually puts a thermometer under every fawcet it passes if it records in range too hot fails not hot enought fails He does not care about the furnace setting unless it is causing the failures Many times re cir pumps are required in extremeny long runs. This has been mentioned in recent post. Another post I posted addrssed the inportance of pipe insulation to prevent heat loss before the fawcet head. Good night its LATE AND TOOK ME A LOT OF TIME TO POST THE LABELING AND LISTING POST INFACT IT WAS SO LONG NOT ALL would post sorry I hit the caps lock
  15. Rhone

    Rhone Minister of Fire

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    That valve they're sending you is a super low-flow valve. It cuts the GPM of your shower from 2.5 to around 1-1.5 GPM. It will save $ in hot water but if anyone in your household has long hair, they're going to hate the amount of time it's going to take to rinse out. Try it, and don't tell anyone it's a super low-flow valve and give it a week. A warning, your family members are going to think you screwed up and wonder why the shower doesn't have the pressure it used to have.

    The reason they sent one is because there are tankless systems that can't keep up with demand. I don't agree with their philosophy and I'll get to that later but I do like dealing with them anyway :) This is what they think may be the reason. Lets say you get a tankless system that can heat 3 GPM on demand. What happens when you have two showers running at the same time using 5 GPM? Your tankless will eventually start to lose ground. So, they sent you a super low-flow valve which only allows 1-1.5 GPM through the valve so it can keep up a little longer. What I don't agree with is that works except for the bit that your boiler guy better have put on a flow restriction valve on your tankless, or your boiler has one built in. If your tankless can only heat 3 GPM with that restriction valve in place it only lets 3GPM through it, ever. If you have two showers at the same time both wanting 5 GPM of hot water, well they both can run and can take indefinetely hot showers but with the restriction valve on your boiler both will have reduced water pressure & flow sharing 3GPM until one or the other stops. Anyway, your boiler can handle more than 3GPM used in my example, a normal tankless system can continously heat 5 or 6 GPM the lower end being 4 GPM.

    Good luck, tell us how it goes.
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    Elkimmeg can correct me if I'm wrong, but a homeowner can do things that a licensed plumber or heating technician legally cannot, per code restrictions.

    As I alluded to in an earlier post, my experience with boiler coils involves circulating water between a coil and a hot water heater. That way it really doesn't matter what the capacity of the tankless coil is, because it's constantly heating water in a 40-gallon tank, making a basically endless amount available on demand. When the heating season started, I would shut the breaker off in the electric water heater and turn the circ pump on. It was wired through an aquastat that would shut off the circulator when boiler temp dropped to the setpoint, and kick back on when the temp rose again. This guaranteed that even if the boiler burned down on a cold night, there would still be a tank full of hot water for showers in the morning. You wouldn't get the temp swings with an oil or gas boiler so you probably wouldn't need the aquastat, although you might want to put one on the water heater side ("breaks on rise") to shut off the pump when it reaches the desired temp.

    I have a different set-up now that doesn't involve a tankless coil. Instead, I have a gravity-feed heat exchanger zoned into the heating system that heats the domestic hot water, so a separate circulator is not required. But I still exchange heat between a wood-fired boiler and a gas-fired water heater (turned way down).
  17. Sundeep Arole

    Sundeep Arole New Member

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    Rhone - that was a very informative post. For sure, Mrs. HotFlame would not be too happy if I made the shower any lower pressure - I'll put in the new stem and try it out, but I may just have to switch back right away.

    Eric - my current system does not have a regular water heater - the DHW comes out of the tankless directly and goes into the kitchen and baths. I like the idea of a backup tank as you suggested, but there is the issue of where I would put it, since I don't have a basement. My boiler actually sits in the kitchen. Another issue is the wiring - I would likely need a dedicated circuit for the heater, and there is no room at the panel. I'd have to upgrade my panel and that would get into serious money quickly. I have however, heard of the small instant water heater units - if those can legally wired into a regular 15 amp circuit which is shared with other things I'd connsider putting in one of those in the main bath for the shower hot water. Or are there any units with a small tank?

    One other thought I had was if I could somehow put a widget in the cold water feed to the shower valve that slightly reduces the pressure of only the cold water at the valve, like a flow restrictor of sorts, I could be able to cheat the valve a little and maybe eek out a little hotter mixture. I doubt this would be something kosher as far as code is concerned, but if all else fails, I'm thinking I'd give that a try. Any thoughts on this idea?
  18. Eric Johnson

    Eric Johnson Mod Emeritus

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    There's no law that says you have to connect a water heater to a power source. Just the insulated tank (and a cheap one would do, at that) is all you need. They sell smaller capacity ones at Lowe's & Home Depot, which look like they hold 15 or 20 gallons. Unfortunately, they cost about the same as the 40-gallon ones. But they're still pretty cheap, and you could probably shop around and find something for even less. And I would say that any storage capacity is better than none.

    One way to do it would be to run water from the tankless heater coil through the tank on its way up to the taps. That would be a little better than your current arrangement, since the water in the tank would be heated whenever you turned on a hot water tap up in the house. A better solution would be to circulate water between the tank and the coil with a circulator. That way you've got 20 or 30 or 40 gallons of water in the tank the same temp. as the boiler to draw from, instead of the 3gpm capacity or whatever the coil's rated throughput is. A little buffer when you've got higher demand.

    On your second point, just put a valve ahead of the fawcet and play around with it. I doubt that's a code violation and even if it is, who's gonna know? Or care?
  19. elkimmeg

    elkimmeg Guest

    One brand is called aqura bost Tank, heated water from you tankless can use a circulator pump or zone valve to feed a booster or storage hot water tank. If you are getting enough hot water now and do not run out often forget that option.
    Wiring any way to add a sub feeder panel? I needed to add some for my new well. My box was maxed out. I believe you can have up to two mini breakers in a 20 slot 100 amp panel. After that either a service upgrade or a sub feeder panel. I used an 10 slot sub panel reason being 2 slots were for the 50 amp breaker to transfere power to the other 8 remaining slots. Really adding any less than 8 slots is a very limited upgrade I also moved out the one mini to the new panel
  20. Sundeep Arole

    Sundeep Arole New Member

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    So looks I like I should try these in the order of least drastic first. I have already tried the set screw - that doesn't quite do it. So the next thing to try is adjusting the tempering valve, if that doesn't do it or water is not enough I wil then go to the valve in cold line or storage tank option. My valve is a TACO 5000 I have posted this url which describes the exact mixing valve I have - but I think the handle is locked down. I'm afraid to force it since I really don't know what I am doing, so by looking at it can you tell me how to unlock the handle andchange the setting? http://www.filterace.com/detail.aspx?ID=953
  21. Eric Johnson

    Eric Johnson Mod Emeritus

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    Not much information on the website. No mention of how to unlock the handle, but I assume that by loosening the allen screw you mentioned, the handle will unlock. Since it's factory pre-set for 130, you probably want to crank it up. If you can't figure it out, try calling or emailing Taco. I've called them before with questions and their tech reps are very responsive and helpful.

    BTW, do you know what your boiler temp is set at? Do you know how to turn it up by adjusting the aquastat?
  22. Sundeep Arole

    Sundeep Arole New Member

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    Eric - I'll try emailing TACO. I looked on their website, find spec sheets, but no instruction manual of sorts.
    There are two boiler settings on the aquastat, hi and low. The hi is set to 180, low to 160.
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