Overheat Advice

[Eric Johnson]

I've overheated every boiler and furnace that I've ever owned, often on multiple occasions. After owning my EKO 60 for more than a year, I finally got around to doing it last weekend. In the process of swapping in the new controller model, I neglected to re-connect the circulator, fired up the boiler, went for a bike ride, and returned an hour and a half later to an overheated boiler.

The last thing you want to do in a situation like this is the first thing your instincts tell you to do, which is to get the pump going and move some cooler water into the boiler vessel. Wrong.

If you do that, and wind up pumping 250-degree (or whatever) water into the rest of your system, you run the very real risk of blowing out any pex you might have plumbed into your piping, damaging pumps and expansion tank bladders, etc. I know people who have blown out underground pex runs in the dead of winter this way. No fun at all.

Instead, do what you can to cool the boiler down to below 200 degrees before firing up the circulator again. Since my boiler is in the barn, I was able to pull a bunch of half-burned chunks out of the firebox and toss them out into the snow, along with a couple shovel-fulls of hot coals. Don't try this if there's anything flammable between the boiler and the water/snow source. I have a manual overheat loop piped into a couple of cast iron radiators in the barn attic, which I opened up to hasten the dispersal of the remaining heat. I also opened the boiler room doors and let cold air circulate around the boiler. Then I went inside and had dinner and a stiff drink (not necessarily in that order).

It took about two hours for everything to cool down to the point where I felt confident re-engaging the pump.

Overheating is not, by itself, going to hurt your boiler. Assuming your pressure relief valve is working correctly, the worst that will happen is that enough pressure will built up in the boiler to lift the valve and vent a big cloud of steam and hot water into your boiler room. Hopefully your makeup water line is open and any lost water will be immediately replaced.

The moral of the story, of course, is to have an automatic, gravity-feed overheat loop plumbed into your system. I have an Automag zone valve for the automatic part, but it's sitting on a shelf in my basement instead of being plumbed into my piping. Silly procrastinator that I am. Barring that, some sort of overheat alarm or power-out alarm is a very good idea. A nightmare scenario for my system (and probably most others) would be a power outage while you're fast asleep, allowing the boiler to overheat, and then the restoration of power a couple hours later, which would result in the unfortunate pumping of excessively hot water into the rest of your system.

Something to think about.

 

[jebatty]

I was observing my Tarm this morning, draft fan cycled off at about 190-195, temp rose to 200 before starting to fall. I have storage, with incoming water from system through a plate hx at 140 at the time, circs running so heat was continually being drawn off the boiler. Temp started to drop from 200 within a couple of minutes. I suspect it could have gone higher and into overheat if I had not been drawing heat off the boiler.

If you have storage, I suspect you do not experience overheat except perhaps when the tank is up to max heat or some error. If you do not have storage, you might want to consider a buffer tank (small storage tank) to take the excess heat when your system is not demanding heat. A new or used hot water tank should work well for this, and I think electric ones are less expensive than gas. No need to wire it up.

Also, to prevent overheat, you might want to set the overheat loop to kick in before the boiler overheats, maybe a 200F trigger. Tarm shuts down from overheat at 210F, and then has to cool to 140F before it can be reset. An overheat loop kick in at 200 may prevent this.

 

[Eric Johnson]

You can do all kinds of effective things if you have power. Not so easy when it disappears.

Actually, I don't have storage and I've never come close to overheating this boiler before. I think my demand is big enough so that circulation alone s sufficient to keep things under control, even when the zones are not demanding any heat. That was with the old controller, which maxed out at 80 degrees C. I think heat loss in my system, in other words, is sufficient to pick up any slack between 80 or 90 degrees C. and an overheat condition.

The new controller, on the other hand, maxes out at 195 degrees F. The controller considers anything over 210 to be overheated. If you run a boiler at 195, there's not much room for it to coast up until you're into the red line.

The radiators-in-the-attic arrangement works pretty well, since it allows the heat to be dissipated through gravity, and the temp differential between the water flowing into the rads (200+ degrees) makes for pretty efficient offloading of heat when the temps in the attic are at or below freezing. The problem is that I can't keep water in those rads or it will freeze. That's why I don't have the Automag (opens on power loss) plumbed in. What I do now is isolate and drain the rads after use. If I need them again, it's simply a matter of opening the valves and letting them fill and circulate. I've considered using something like an old water heater where the water temp could be maintained at something above freezing instead of the rads. 50 gallons of 40-degree water would probably be sufficient to handle the 30 or so gallons in my EKO.

 

[Dave T]

Good to hear you were able to get the EKO back under control Eric, I replaced my pump a few days ago and when I did I removed the in line flow check valve that I installed when I put the system together and replaced it with a Y strainer because my circ runs full time and the flow check was self defeating on my system..I also have 2 house zones for an overheat situation, I don't know if it got used the other night but I woke up to the overheat light on and the boiler in idle with the circ pumping away, the boiler was already down to 68* celsius..BE READY IT WILL HAPPEN TO YOU TOO...Dave

 

[Sizzler]

Sorry to hear about the overheat Eric.. What in the world were you thinking riding your bike in December on the snow covered roads of NYS?? Are you sure you didn't have the stiff drink first, forgot to rehook the circ, and then decide a bike ride would be a good idea :<)


Seriously though, how hot did you actually get?

 

[Eric Johnson]

The overheat is no big deal. I don't know how hot it got, since the controller displays the "Overheat" code above 210. But it was boiling pretty good. The pressure stayed down around 20 psi, however. Apparently the temp side of my old analog temp/pressure gauge doesn't work. Like I said, I've done it many times before with other boilers and as long as you don't panic and do something stupid (BT,DT), everything works out in the end. Forgetting to hook the pump back up is a long, long story, but let's just say it has to do with my severe limitations as an electrician and my innate inability to leave well enough alone. Heating system "upgrades" are always an exciting adventure around our house.



About the bike ride: It was about 45 degrees and the roads were clear and mostly dry, so I figured I'd try to get one more ride in before the Big Snows. Couldn't ski and needed to work off some of those holiday calories. I had a nice, 30 mph tailwind on the first half (headed east), then looped around and headed home into the wind. All downhill but still pretty cold and pretty slow going. On balance, not a bad 22-mile ride, but it had some interesting moments. We've had about a foot and a half of fresh snow since then (more on the way) and it's supposed to get down around zero tonight. So I guess I'll be strapping the boards back on this weekend.

 

[WoodNotOil]

I have a DHW coil in my Tarm and I am on city water that has backup power incase of an outage. I just run the hotwater faucets and draw the temp down that way.

 

[free75degrees]

On my second tarm burn the temp went over 200 because the termovar was clogged. I was really scrambling for what to do so I got a couple 5 gallon buckets and emptied some hot water from the boiler drain. I was effectively replacing the water in the boiler with much cooler water from the rest of the system. Do you think this is ok? Is it possible that the cold water replacing the hot water in the boiler could do some damage?

 

[heaterman]

Overheating will definitely get your attention in a hurry. A customer that we had installed a boiler for a while back hired an electrician to install a transfer switch for a gen set which of course necessitates killing the power to the whole place. They did so while a full burn was underway in the boiler and discovered the minor oversight when the relief valve let go enveloping everything in a cloud of steam. IIRC he dumped hooked a garden hose to the boiler drain at the bottom of the unit and dumped hot water from a high point in the system. He has plans for an automatic overheat loop as we speak.

BTW Bellimo makes 24V and 110V zone valves that work great for gravity flow dump zones. They have a 3/4" sweat or NPT body with a CV rating of 5 which simply means it will flow with very little restriction. 2 year warranty and around 125-140 shekels.

 

[heaterman]

On my second tarm burn the temp went over 200 because the termovar was clogged. I was really scrambling for what to do so I got a couple 5 gallon buckets and emptied some hot water from the boiler drain. I was effectively replacing the water in the boiler with much cooler water from the rest of the system. Do you think this is ok? Is it possible that the cold water replacing the hot water in the boiler could do some damage?

On a light construction unit with a lot of sheet steel flooding it might cause cracking but I doubt it. On a unit like a Tarm I can't see that it would cause that much stress. The one thing you want to watch in that scenario is that you house pressure is sufficient to overcome the pressure in the boiler. You'd be surprised at how much pressure drop occurs in a 50' length of 5/8" garden hose.

 

[Mushroom Man]

I am still slowly plumbing my system.

The gravity-fed dump zone seems to be recognized as an OPTION. For me it is a NEED. Some would say I'm being paranoid but peace of mind is important to me.

I am unclear as to how a dump zone really works so I am going to throw out some thoughts and hopefully the braintrust here will correct any misconceptions I have. I have acquired 2-50 gallon sealed steel drums and am intending to plumb them into the boiler loop with an automag zone valve(set at 200).

Here are my understanding of how it would work:

In the event of a power shortage while the boiler is in burn mode and the storage tank is at or near capacity temperature

1. the boiler temp would increase to 200 degrees
2. the automag would open if set to 200 degrees
3. the hot water surrounding the boiler would, by convection, (hot water moving to cold water) mix with the 100 gallons of cooler water (say 70 degree water) in the dump loop (barrels). The hundred gallons could absorb (100 gals.*8.3 lbs.*130 degrees) =107900 btus per hour.
4. the 47 gallon capacity boiler is overheating (200 degree instead of 180 degree, a net difference of 20 degrees) because it is producing (47 gals.*8.3 lbs.*20 degrees) =7802 btus per hour too much heat.
5. the fan driving the burn process will be off (no electricity) so the burn will be starved or almost starved of oxygen so will be reduced in intensity dramatically
6. the 100 gallon overheat loop should be adequate to dissipate the heat

There is a large thermal storage tank (1500 gallons unpressurized), a battery/generator power failure provision and of course a relief valve; but I'd sleep more comfortably knowing that the gravity fed loop would solve the overheat situation.

 

[Duetech]

(Just FYI) I know that tuning the EKO to burn better is the ideal for run time and btu out put and that the secondary air setting is part of that. However to help cool down the overheated boiler you can close down the secondary air supply which is a continual source of oxygen to the fuel supply and if you know your settings you can reset the secondary air supply prior to restarting the boiler.

 

[flyingcow]

I'm hooking up fin tube(mount high on wall in boiler room), with an auto mag. Power's off, valve opens dispenses heat. I've got to have 10% of boiler output for fin tube. Tarms layout. I think that's more than adequate.

 

[ohbie1]

I was sick of plumbing work after hooking up the Tarm to the oil boiler and storage tank, so I took an electrical approach. A deep cycle battery(75 AH) with 200W inverter and a couple of relays that run the circulators in the event of a power failure. This will run things for 3+ hrs.

 

[Donl]

I am still slowly plumbing my system.

The gravity-fed dump zone seems to be recognized as an OPTION. For me it is a NEED. Some would say I'm being paranoid but peace of mind is important to me.

I am unclear as to how a dump zone really works so I am going to throw out some thoughts and hopefully the braintrust here will correct any misconceptions I have. I have acquired 2-50 gallon sealed steel drums and am intending to plumb them into the boiler loop with an automag zone valve(set at 200).

Here are my understanding of how it would work:

In the event of a power shortage while the boiler is in burn mode and the storage tank is at or near capacity temperature

1. the boiler temp would increase to 200 degrees
2. the automag would open if set to 200 degrees
3. the hot water surrounding the boiler would, by convection, (hot water moving to cold water) mix with the 100 gallons of cooler water (say 70 degree water) in the dump loop (barrels). The hundred gallons could absorb (100 gals.*8.3 lbs.*130 degrees) =107900 btus per hour.
4. the 47 gallon capacity boiler is overheating (200 degree instead of 180 degree, a net difference of 20 degrees) because it is producing (47 gals.*8.3 lbs.*20 degrees) =7802 btus per hour too much heat.
5. the fan driving the burn process will be off (no electricity) so the burn will be starved or almost starved of oxygen so will be reduced in intensity dramatically
6. the 100 gallon overheat loop should be adequate to dissipate the heat

There is a large thermal storage tank (1500 gallons unpressurized), a battery/generator power failure provision and of course a relief valve; but I'd sleep more comfortably knowing that the gravity fed loop would solve the overheat situation.

The automag will open with the loss of power. They are a valve that is normally open when power is applied and will close with the loss of power. If you want the valve to open at 200 degrees apply power to the automag from an aquastat. This will remove the power from the automag when the set temperature is reached. This way the overheat loop will be activated for either a power failure or an overheat condition.

If the system is pressurized I don't think sealed steel drums would be appropriate.

I agree with you that this is an important safety issue. The design of good overheat protection must consider all possibilities so the system can be brought down gracefully all by itself when no one is around.

 

[Gooserider]

Well the first question that comes to my mind is what happens to a boiler when the power fails? How about if it goes into overheat mode for some other reason? - Does it shut down the draft so that the fire goes out (ideal) or at least greatly reduces it's burn rate (not so good, but tolerable)?

Then presumably one has an over heat loop - I was thinking a bunch of otherwise unused baseboard / fin tube attached to the ceiling - roughly how much length would this need, and would it be enough to do a gravity dump?

Alternatively, could one plumb the radiant floor loop (presumably PEX tubed) of the room above the boiler to also function as a dump zone?

I am assuming that in either case the room above is going to get seriously hot, but IMHO that is acceptable as an emergency scenario...

How is all this likely to interact with the rest of the plumbing - how does it tie in?

Is the automag valve something that is purely a thermal trigger, or does it require some constant amount of electrical current to keep it from opening?

Gooserider

 

[Donl]

Is the automag valve something that is purely a thermal trigger, or does it require some constant amount of electrical current to keep it from opening?

Gooserider

It requires a constant amount of electrical current to keep it open.

 

[cguida]

As long as this subject (overheated boilers) is at the top of the thresd list, allow me to offer this not very well-considered thought and tell me what you think might be wrong with it.

Why not use the whole house as an over-heat dump zone? Suppose you wired together parallel lines to all the thermostats, and then controlled these two ends of a "Grand Unified Thermostat" by means of an aquastat relay on the output of the boiler. Should the boiler get seriously ahead of house heat demand, and creep up to some danger zone (200+) degrees -- then the aquastat would close, and the whole house would get a few degrees warmer. You might notice it. You might not. But the whole house would most likely act to keep the boiler to a safe level -- and do it reletively quickly.

I realize this won't help in event of a power failure. Otherwise, what's wrong with this plan? Seems pretty simple, and simple to impliment.

 

[Mushroom Man]

Hi Don:

Thanks for that info on the automag. That is helpful and my understanding was wrong.

I was wondering why you thought the steel drums were inappropriate. They are heavy gauge leak-proof barrels with black pipe fittings inserted into the fittings in the barrels. Remember that for most of their lives they will contain room temperature PH-conditioned water and will be under ambient pressure.

Granted that, in the event of an overheat situation the pressure is likely to rise; but I doubt that it would rise sufficiently high to breach the drums, especially with a pressure relief valve set to 30 psi in the system.

 

[jebatty]

It requires a constant amount of electrical current to keep it open.

Just the opposite. Power closes the automag so no water flows. Loss of power opens the automag to allow water to flow into the overheat zone(s).

 

[Donl]

It requires a constant amount of electrical current to keep it open.

Just the opposite. Power closes the automag so no water flows. Loss of power opens the automag to allow water to flow into the overheat zone(s).

Thanks Jebatty, I should have read my response more closely before sending it!

 

[Donl]

Hi Don:

Thanks for that info on the automag. That is helpful and my understanding was wrong.

I was wondering why you thought the steel drums were inappropriate. They are heavy gauge leak-proof barrels with black pipe fittings inserted into the fittings in the barrels. Remember that for most of their lives they will contain room temperature PH-conditioned water and will be under ambient pressure.

Granted that, in the event of an overheat situation the pressure is likely to rise; but I doubt that it would rise sufficiently high to breach the drums, especially with a pressure relief valve set to 30 psi in the system.

Hi Tim

I try to over design most of my projects, especially in areas where I don't have a lot of experience. What pressure are the steel drums rated for?

Remember, when that automag opens, the steel drums will will be subjected to full system pressure. Depending on your design the steel drums may be under system pressure all the time, even with the automag closed. In an extreme overheat condition the pressure may become quite high. If those drums can't handle the pressure (even below 30 lbs) there may be a big bang. To make my point, when I tested my 500 gallon propane tank I put in 20 psi. Being stupid, I unscrewed one of the black pipe fittings to relieve the pressure. I was lucky not to get my head blown off I now fully respect pressure!

Also when the pressure is suddenly dropped to 15 psi, The overheated water that was not boiling under high pressure may expand rapidly adding to an already bad situation.

FYI I used an old 50 water heater tank for my overheat loop.

Don

 

[Gooserider]

It requires a constant amount of electrical current to keep it open.

Just the opposite. Power closes the automag so no water flows. Loss of power opens the automag to allow water to flow into the overheat zone(s).

Thanks Jebatty, I should have read my response more closely before sending it!

Either way, this seems like rather a negative to me... One of the things I would consider a strong design requirement is to minimize the use of electrical power in the system - thus I would want to see things like valves that only require power to CHANGE state, not require constant power to keep an open / closed status, circs that only run when there is a real demand, etc... (Even if the amount needed is small, it still adds up over time...) I see little point in going to all the hassle of installing a wood burner to keep from giving money to the "fossil fuel guy" if you end up giving it to the "electric guy" instead...

In the case of an automag, it seems like the valve is really sort of triggering on the wrong condition - it is opening the heat dump on loss of power, not on overheat... But loss of power doesn't automatically mean overheat - what about if the boiler is not burning? Or is just getting started, or near the end of a burn with the temperature on the low end... If the draft stops and the fire goes out / dies down, it seems quite possible that the boiler would never go into overheat, and thus wouldn't need the dump zone...

Is there any kind of valve that is non-powered, and that would open fully and fairly fast once a critical temperature was reached, and not before? (i.e. the hydraulic equivalent of a "snap switch") While an auto-reset would be nice, manual reset would be acceptable... It would seem like that would be a far better option than the automag - no power consumption, and triggers on the condition that represents the need, not one that might or might not represent an actual need...

Gooserider

 

[Gooserider]

Hi Don:

Thanks for that info on the automag. That is helpful and my understanding was wrong.

I was wondering why you thought the steel drums were inappropriate. They are heavy gauge leak-proof barrels with black pipe fittings inserted into the fittings in the barrels. Remember that for most of their lives they will contain room temperature PH-conditioned water and will be under ambient pressure.

Granted that, in the event of an overheat situation the pressure is likely to rise; but I doubt that it would rise sufficiently high to breach the drums, especially with a pressure relief valve set to 30 psi in the system.

Hi Tim

I try to over design most of my projects, especially in areas where I don't have a lot of experience. What pressure are the steel drums rated for?

Remember, when that automag opens, the steel drums will will be subjected to full system pressure. Depending on your design the steel drums may be under system pressure all the time, even with the automag closed. In an extreme overheat condition the pressure may become quite high. If those drums can't handle the pressure (even below 30 lbs) there may be a big bang. To make my point, when I tested my 500 gallon propane tank I put in 20 psi. Being stupid, I unscrewed one of the black pipe fittings to relieve the pressure. I was lucky not to get my head blown off I now fully respect pressure!

Also when the pressure is suddenly dropped to 15 psi, The overheated water that was not boiling under high pressure may expand rapidly adding to an already bad situation.

FYI I used an old 50 water heater tank for my overheat loop.

Don

Actually, I would expect the overheat loop to be under system pressure at all times... As I understand it, the dump loop should be a gravity loop, which means it's a complete circuit, with the automag only on one end, and the other end open to system pressure. If this wasn't the case, then you would need to put an additional expansion tank, pressure relief, etc. on the dump zone since it would be "sealed" when the automag was closed...

In terms of pressure testing, I don't know what the official "code" spec is, but apparently the EU spec on boilers meeting EN-303-5 is a 60psi static pressure test, with a maximum operating pressure (as set by the required pressure relief valve) of 30psi. If I were testing a system, I would definitely want every component in the system to meet AT LEAST the 60psi test that the boiler did... Given that my compressor will do about 110psi, I would probably test to that for everything except the boiler and any other components that I knew were only spec'd to handle lower test pressures...

I want to be sure that I know where the "failure points" in the system are - by making sure that everything EXCEPT the designed in pressure reliefs can handle a lot more pressure...

Gooserider

 

[Donl]

Hi Don:

Thanks for that info on the automag. That is helpful and my understanding was wrong.

I was wondering why you thought the steel drums were inappropriate. They are heavy gauge leak-proof barrels with black pipe fittings inserted into the fittings in the barrels. Remember that for most of their lives they will contain room temperature PH-conditioned water and will be under ambient pressure.

Granted that, in the event of an overheat situation the pressure is likely to rise; but I doubt that it would rise sufficiently high to breach the drums, especially with a pressure relief valve set to 30 psi in the system.

Hi Tim

I try to over design most of my projects, especially in areas where I don't have a lot of experience. What pressure are the steel drums rated for?

Remember, when that automag opens, the steel drums will will be subjected to full system pressure. Depending on your design the steel drums may be under system pressure all the time, even with the automag closed. In an extreme overheat condition the pressure may become quite high. If those drums can't handle the pressure (even below 30 lbs) there may be a big bang. To make my point, when I tested my 500 gallon propane tank I put in 20 psi. Being stupid, I unscrewed one of the black pipe fittings to relieve the pressure. I was lucky not to get my head blown off I now fully respect pressure!

Also when the pressure is suddenly dropped to 15 psi, The overheated water that was not boiling under high pressure may expand rapidly adding to an already bad situation.

FYI I used an old 50 water heater tank for my overheat loop.

Don

Actually, I would expect the overheat loop to be under system pressure at all times... As I understand it, the dump loop should be a gravity loop, which means it's a complete circuit, with the automag only on one end, and the other end open to system pressure. If this wasn't the case, then you would need to put an additional expansion tank, pressure relief, etc. on the dump zone since it would be "sealed" when the automag was closed...

In terms of pressure testing, I don't know what the official "code" spec is, but apparently the EU spec on boilers meeting EN-303-5 is a 60psi static pressure test, with a maximum operating pressure (as set by the required pressure relief valve) of 30psi. If I were testing a system, I would definitely want every component in the system to meet AT LEAST the 60psi test that the boiler did... Given that my compressor will do about 110psi, I would probably test to that for everything except the boiler and any other components that I knew were only spec'd to handle lower test pressures...

I want to be sure that I know where the "failure points" in the system are - by making sure that everything EXCEPT the designed in pressure reliefs can handle a lot more pressure...

Gooserider

I also would expect, or assume the overheat loop to be under pressure at all times. However, if a check valve is placed on the opposite side of the overheat loop (as per some documented designs) , that may effect what pressure the overheat loop is subjected to. The safest approach to this is to assume the the overheat loop is always at system pressure, therefore it should meet the same overall system specs.