Hydronic heat system trouble

Last week it got cold, so I turned on the heat for the first time this season. I have a gas fired Crown furnace. Perhaps a half hour to 45 mins later I hear pinging in the basement. I go downstairs and there is steam and boiling water shooting out of the pressure release pipe. The pressure gauge read somewhere over 30 psi and the temp around 240. I could hear water boiling in the pipes. I figured the water wasnt circulating properly. So after allowing everything to cool down for a bit, I turned the system back on to check the circulation pump, which I confirmed was running. Since I don't know a lot about furnaces or hydronic systems, I called my gas company to come check it out. I wasn't able to be home at the time, but my wife explained to him what had happened. He was there for about 10 minutes, told her the furnace was fine and that the issue was with the plumbing, likely with the fill valve not giving enough pressure to circulate water through the system. What? That makes 0 sense to me. Doesn't the fill valve just ensure that if the system needs more water it gets it? I don't think this guy knows what he's talking about. I think, since the circulation pump is working, that my furnace is overfiring. I don't have much experience dealing with furnaces, but am handy enough to fix things. I would appreciate any help getting to the root of the problem. Thanks in advance.

 

Crown model number AWI12BSNST1PSU.

 

It is possible the system is low on water but it also would appear that you have a problem with your aquastat. The aquastat's job is to regulate the boiler temperature based on mode and demand.

I could not get your model number to work. Please double check that.
A few pictures of the plumbing around your boiler will help us to help you with what to check.

http://www.doityourself.com/forum/el...-pictures.html

 

First of all, in residential heating a furnace heats air that is distributed by a blower through ducts. You have a boiler.

You need a certain minimum amount of pressure in the system for proper operation. Your pressure gauge and/or thermometer mounted on the boiler may be be severely out of calibration. Since water cannot be compressed you also need room for it to expand when it is heated. Somewhere in the system is an "expansion tank" that has both air and water inside. There are two types of expansion tanks, one will be a tank similar to a propane barbecue tank generally hanging from one of the main pipes. The other will be a much larger tank that is placed between the floor joists.

As PJ requested we need several pictures of your installation to proceed. Pictures MUST be IN FOCUS AND WELL LIT or they are useless. Close up pictures are NOT needed at this time (maybe later) but I need to see wide angle or from a far enough distance to see how the various parts are connected.

 

Also if your boiler was 240F then the aqua-stat is probably not working correctly also. On top of the 30 psi issus which can be exp tank or fill valve..

 

Sorry, B should have been an 8. Crown AWI128SNST1PSU

 

The pressure/temp are cold readings... so the current 110 reading appears high I'd imagine.

 

You have a diaphragm type expansion tank. It is the grey tank hanging from the piping over the top of the boiler. On the bottom of that tank is a tire valve, remove the dust cover and momentarily press the pin to see if air or water comes out. If water, the tank is shot and needs to be replaced.

After turning the electrical power OFF remove the cover of the grey box on the front (or maybe it is the side) of the boiler. There will be at least two, maybe three temperature settings inside. See what the highest setting is, it should be no more than 180 degrees. Post a clear close-up picture of the insides of this control.

Feel the pipes as close as possible to the boiler to see if they feel close to the temperature indicated on the boiler gauge.

Post back with the results.

 

Ok so I checked the expansion tank and it's just air coming out, minus a tiny bit of condensation. I felt the pipes, and the one coming from the expansion tank is warm, probably close to the 100 degrees the temp gauge now reads. I removed the cover and took a few photos of the aquastat as directed. I looks to be set at 180, but I do see a 200 mark on the dial.

 

The aquastat is a honeywell L8148E

 

The brass device at the top of this pic is the fill valve... Center top of pic. Find the valve on this line and turn it off. This is the water feed for the boiler.

[ATTACH=CONFIG]72699[/ATTACH]

Turn off power to boiler.

Then drain some water out of the boiler out the bottom of the boiler drain. The pressure should go down some. Lower pressure to 12 psi.. This also will verify that the gauge moves..

[ATTACH=CONFIG]72700[/ATTACH]

Leave the fill valve off.

Then power up the boiler and turn a t stat up all the way... Watch the boiler temp and pressure.

If pressure rises up near 30 psi shut it down. ( Most likely exp tank issues and need to add air or replace)

If pressure stays good but temp rises higher then 180f you need to lower the aquastat . The boiler should stop firing at 180 f.

If adjusting that wheel up or down has no effect the aqua-stat is bad. ( Means the boiler is in runaway mode and will continue to rise in temp and pressure until the relief valve trips..) Then shut it down.

Lets start there.

 

I shut the line from the fill valve off, then I drained boiler to what looks like about 13 psi in pic. Next pic is pressure at 180f. Last pic is when water began to come out of the relief, and when I shut it down. Next I will try moving aquastat temp to 160 and see what happens.

 

Water came out of relief valve because the pressure went up to 30 PSI, which is what it should do. Most likely your expansion tank has lost most or all of its charge. If you can't isolate it to check the charge, there should be at least 12PSI, you can pot a small charge in it in place and see what happens or you can remove it and see if it will take a charge or replace it. Don't let any more air out of the shrader valve, you'll only make the problem worse. Tap the tank when cold, top should be solid, bottom, hollow. Check when hot, if both sides are solid the tank is water logged and should be replaced.

 

The system is still hot from before, and I tapped both sides of the tank and it sounds different, so I assume there is at least some air on the bottom. When I let a bit of air out before, only air and the tiniest bit of water came out, which to me seemed like condensation. Now, being a closed system, to check the air pressure in the expansion tank wouldn't I be able to open the valve from the fill valve(currently closed), and open a faucet somewhere, and get an accurate air pressure reading?

 

No, absolutely not. You have to depressurize the water side of the tank down to atmospheric, and then check the air pressure. This may or not require depressurizing the whole system, depending upon your valving.

 

Yeah I would just go ahead and replace the expansion tank... Make sure the new tank has 12 psi in it before you install it..

After that make sure you adjust the aquastat so the burner stops firing when the temp gauge reads 180..

 

I tend to agree with Mike. But, to replace the tank you will first have to depressurize the water side, so just for grins, check the air pressure in the tank.

It's very important to check the air pressure in the new replacement tank before it is installed. Bladder-type tanks continuously lose pressure due to diffusion of air through the bladder - whether the tank is installed or sitting on the shelf before installation. Within a few years, it will be flat.

 

I do have valving that will allow me to shut off most of the system, but not right around the expansion tank unfortunately. A few questions.

Would an expansion tank failure cause the system to rise above the 180f the aquastat is set at? Is there a possibility that the aquastat is the root cause, and the added pressure caused the expansion tank to fail? I am sure the water was boiling in the pipes initially, and therefore had to be above 180.

Should I turn down the aquastat and retest that it shuts off at some point before replacing the expansion tank?

Is an expansion tank supposed to ensure your system pressure doesn't rise? Does a rise in pressure mean the tank is either undefiled or bad?

The system was previously set at 20 psi, is that because it's two floors? Shouldn't I put 20 psi in the new tank and restore the system to 20 psi?

I just want to be sure there isn't two problems before replacing the expansion tank.

 

No.

No.

No, 20 psi is a bit higher than necessary for two floors plus a basement. 15 psi is about right, but 20 psi is OK.

 

Your aquastat in itself would not likely make the pressure rise. It would really have to run away with the temp. Water boils at 212 deg at 0 psi. It takes about 240 deg at 12psi, so yes you should definitely make sure that is working. The expansion's tanks sole purpose is there to take the heated, expanded water from the boiler as the overflow tank in a car does. Without it the water would have no place to go creating pressure and at 30psi would blow the relief valve.
About the 20psi, I run my systems at 20. I find there's less cavitation in the pumps and I think better performance with 2 stories or any system. On paper 12-15psi would get you there but it's just my preference. A while back TACO came out with a statement saying they recommended all systems run at 20psi that have wet router pumps which is what your 007 is.
Lastly, although I hardly ever see it mentioned your expansion tank pressure SHOULD match your system pressure. In other words if you're going to restore your pressure back to 20psi put 20 into your tank before you install it. Hope this helps.

 

Just to clarify, gilmorrie stated that an expansion tank failure would not cause the system to overheat, which it absolutely is doing (240f and boiling in the pipes as I first posted). If that's the case, wouldn't my aquastat be bad? The setting hasn't been moved since I bought the house three years ago, and it hasn't done this before.

 

gil is correct in saying the expansion tank has nothing to do with the overheating and the aquastat not shutting down on a set temp. You can try lowering the aquastat and see if it operates any better but if it doesn't you have a bad control. You can check and make sure the sensing bulb is inserted into the well properly. They do wear out. If everything looks good change the aquastat.

 

After allowing the system to cool, I changed the setting on the aquastat to 150, and it never shut off up to 200 when I shut the system off. So I'm inclined to believe it's not the expansion tank, it's the aquastat. I'll see if I can figure out where and how to check the sensing bulb tomorrow as its getting late for me.

 

FYI it's probably both. I'm sure you'll be changing the exp tank after you change the aqua stat.

 

Also now may be a good time to put in a more efficient aqua stat that automatically lowers and raises the boiler temps.

 

There is no way to check the bulb and its not replaceable anyway. I would change the aquastat. On another note you're probably going to end up changing or charging the expansion tank also because you tank has nothing to do with your boiler not shutting down.
When you shut your boiler down at 200 deg. what was your pressure reading. If it was at 30psi and leaking that should tell you it's not the control doing it because 200 deg. is well within the range of proper operation and should keep your pressure steady.

 

Those are commonly called out-door-reset. ODR's have two temperature sensors. One goes in the aquastat fitting on the boiler and the other on an outside house wall.

OCR's adjust the boiler water temperature raising it from 140F in warm weather to 180F on very cold days. They have many set up features that optimize the operation for variables in different homes.

A best buy is the Tekmar 256 that goes for $150 on Amazon.com and SupplyHouse.com


Look up the Tekmar 256 manual on their site. ODR's actually make homes more comfortable and lower fuel costs.

ODR's units from Honeywell, Taco and Beckett are part of a system that costs many $100's to put together. In fact the Taco PC 700 for $257 is a rebranded Tekmar 256 with a 4 conductor connector. To use it you have to buy other Taco units to plug it into for hundreds of dollars more.

 

In most cases, a residential hot-water boiler will be oversized. But, it is also common for the radiation to be oversized - it can put out more heat than the maximum required on the coldest day, at, say, 180 deg water temperature.

If a system is over-radiated, then there is no reason to increase the water temperature during very cold weather. The boiler's efficiency and net Btu output will decline with a higher water temp. Best to run the boiler at the lowest temperature that will avoid condensation in the flue and still heat the house. In many cases, that means to run a constant boiler temperature throughout the heating season.

This basic fact is often overlooked, particularly by marketing pitches for expensive outdoor reset controls. And, ODR is a system complication that may invite potential problems.

 

Home owners do not have to worry about being “over-radiated.” Their room temperate thermostat limits the heat radiation to its setting.

Over-radiated does not seem to be an issue in the US even thought an often sited statistic is that 85% of US home boilers are twice the size needed. Further reducing the threat is that they run only 20 % to 25% of the time on coldest days.

The whole idea of out-door-reset is adjusting boiler water temp to what is actually needed for the outdoor temperature on any given day. One of the ODR set up fields is max temp. So if the outdoor temp drops to -50F ODR will not raise water temp above max temp setting regardless of how cold it is outside.

The boiler temp necessary to maintain room temp thermostat setting on coldest days is not some arbitrary, idle number. BTU's radiated is a function of water temp, gpm circulated and radiator/convector characteristics. Since the latter two are fixed, water temp is key to BTU's delivered. That is why the ODR setup has fields for data on various items in the building heating system to optimize operation.

Reading the Tekmar 256 ODR manual will show the many features and benefits ODR's offer. By reducing the firing rate of my 60 year old boiler to 50% of rated it runs very efficiently at 85%. On coldest days it runs 25% of the time. So homeowners to raise efficiency do not replace that old oil burner, just reduce firing rate with a smaller $5.00 nozzle. It many not be as profitable for the oil company but home owners will appreciate the $$$$ savings.

This not marketing hype. It is about an effective, comfortable and cost effective heating system.

 

Consider this scenario: It's the coldest day of the year. The boiler setpoint is 160 deg, and it's maintaining the house temp at 72 deg, and the boiler burner is cycling on and off. Should we then raise the boiler setpoint to, say, 180 deg - at a lower boiler efficiency and lower net heat output?

 

At some point in that scenario the $.25 per KWH electricty cost to run circulator longer may be more than oil costs to keep water hotter. But it misses the key point of OCR's which are constantly adjusting the water temp to changing outdoor temp. And.. the OCR setup allows for a max setting so you can have it both ways. Keep set it at 160F max or whatever.

My system with significant over capacity, is optimized so it uses 50% less oil than others in this area.

The wife sets the thermostats to whatever she wants, has plenty of hot water and likes the low cost.

I now have other DYI projects to play with.