Pressure rises rapidly


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Old 09-09-07, 06:55 AM
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Pressure rises rapidly

Hopefully this is the right forum area...

My setup is a wood burning furnace and an oil boiler hooked up to baseboard heating. I use the wood until it gets so cold that it can't heat my whole house anymore, then switch to the oil.

The problem is that the wood furnace pressure gage started rising rapidly when I would start a fire in it. This caused the pressure release valve on the back of the oil furnace to go off (closed system, over 30psi). So what would cause the pressure in the wood furnace to rise so rapidly? Is there some sort of part inside that could be bad? The wood furnace is about 30 years old.
 
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Old 09-09-07, 10:58 AM
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What's the status on the expansion tank?
 
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Old 09-09-07, 01:46 PM
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I believe you're talking about the big tank hanging from the pipes. It doesn't have any type of structure on it that would tell me anything. I'm new to this type of system (always had gas/forced air heat).

What I know is that it's only 2yrs old. It was put in when I got a brand new oil burner 2 yrs ago. Is there something that I should be doing with it? It's got a knob on the bottom.

It's also located on the same pipes as the oil furnace and that hasn't had any problems when it's in use.
 
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Old 09-09-07, 07:12 PM
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Pictures

If you can take a few pictures of the boilers & nearby piping, including the tank, it would be a big help. Since we can't post pictures here, you can post them on Photobucket.com or similar photo sharing web site & post the URL to them here.
 
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Old 09-12-07, 05:06 PM
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Old 09-12-07, 09:26 PM
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High Pressure

Are you sure all valves between the expansion tank (extrol) & the wood boiler are open?
 
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Old 09-13-07, 07:53 AM
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Yes. I'll describe how this first started a little better.

I had been using the wood furnace for a couple months in winter '06 (this is after using it a lot in winter '05). I had no issues with it, then one day I noticed water on the floor of my garage. It wasn't a lot so I didn't think to much about it (stupid, yes). Then one night I heard the pressure release valve pop and water was spraying all over my garage, and it wasn't stopping. I had to cool down the wood furnace by taking the wood out. Then the pressure dropped.

I got everything back in working order and have since not used the wood furnace because of the rapid rise in pressure once it starts heating up.

Is there a part in the wood furnace itself that could need replacing?
 
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Old 09-13-07, 09:23 AM
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What you need to do is make sure your expansion tank's bladder is still intact.

If you can isolate the expansion tank with a valve, then shut that valve off and then with someone fully supporting the tank (and fully assume and expect that it is full of water - if not that'll be a good surprise - rather than an injury) twist it out using a wrench (not the tank itself).

If the tank is full of water, it's garbage. Get a new one, pump it up to 15 psi or so (varies with your house height) and then twist it in.

Since you're using a wood fired stove, I'd actually think about installing a second expansion tank and also extended the piping of them lower so that the diaphram isn't dealing with as rapid of temperature changes.
 
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Old 09-13-07, 10:39 AM
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Ok, you wanna hear something stupid now? When I was having all my problems and water was going everywhere, one of the things I did was to take off the cap at the bottom of the expansion and push that nozzle in letting air out. That's what people do when they have no idea what they're doing....they guess at the problem.

Of course that was after it was all ready having rising pressure issues.

So perhaps I worsened it with letting air out. Maybe I'll try to put air back in before taking the tank off (because my numerous pipes and valves are a hassle to figure out). In fact I'm not sure that I could isolate the tank without having to empty the hole system of water.

And guess at the psi? I'm located in Western New York at roughly 1,730 ft above msl.

And as always -- thanks!!
 
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Old 09-13-07, 11:01 AM
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The most accurate way of setting the air pressure is with the tank disconnected. If there isn't a valve right before the tank you may want to drain down enough so that you can remove the tank and add one.

As for the pressure, I was just talking inside the house height factors. You want 5 psi at your highest point and then figure out what that requires where your boiler pressure gauge is located. If you aren't in 3 storey house then 15 should be fine.
 
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Old 10-25-07, 10:56 AM
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Ok, the tank is set to 13psi, the bladder is still intact, and I have a 2-story house. So everything should be fine there.

Any other ideas?

Is there an actual part in the wood furnance that controls pressure? It's old, so perhaps something went.
 
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Old 10-25-07, 11:07 AM
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Has the expansion tank actually been sized for the number of gallons and the temperature rise? You may need a second expansion tank...

Extrol and Watts have online calculators for this.
 
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Old 10-25-07, 04:19 PM
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Give me the old style tank anytime. No maintenance no worry
 
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Old 10-25-07, 04:22 PM
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Originally Posted by Kritheon
Is there an actual part in the wood furnance that controls pressure? .
Nobody seems to have answered this...

No.

Pressure is controlled by the feedwater regulator, but that just sets the minimum pressure in the system. (to a nominal 12-15 PSI usually). As the system heats, if the expansion tank is properly sized, and has the proper air charge in it, the tank will act as the 'cushion' to keep the pressure in the system from sky-rocketing when the water is heated. Normally, you will see a pressure increase of say 3-5 PSI from cold water to hot.

Who talked about adding a second tank, or increasing the size of the existing one. You could well have a large volume of water in that system that requires a larger tank.

What type of heat emitters are in the house ? Baseboards? Radiators ?

I'm not sure why the oil-fired boiler wouldn't cause the same problem, unless there are valves that are closed and should be opened when running the wood boiler. The temp rise on the wood boiler is very likely higher than the oil, and this could be part of the problem.

Did you mention what the pressure in the system is when cold ? This is important, because if it's too high, it will blow the safety valve even if the tank is OK. You could have a defective (or improperly set) feedwater pressure regulator.

I couldn't see a durn thing in them cellphone camera pics... blurry, bad light...
 
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Old 11-06-07, 10:21 AM
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Thank you for the info!

When cold, the system is about 13psi.

Since it's now getting cold in WNY (just snowed last night) I was able to try things out again. The oil furnace lights fine and heats up the entire house. The PSI hovers around 20 when it's been on for awhile and it's really hot.

So I tried the wood furnace again as well (before turning the oil on). The wood furnace would get really hot and the pipes coming out of it would be hot as well, but only up to about 2 ft, then the pipes would be cold. So it seems that the wood furnace is heating the water but the water isn't getting pumped to anywhere, hence the pressure building up once the fire gets hot enough.

I have 3 pumps for this system and they all sound like they're working, that is I can hear them when they're turned on. Perhaps that doesn't mean that they are working. Does that sound like something to check out?
 
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Old 11-06-07, 12:51 PM
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i'm not real familar with wood burner boilers, but would think that you would need a type of bypass/overheat loop or a storage tank so you wouldn't start boiling the boiler water when the the heating circuit wasn't calling for heat.

So it would either be a gravity fed loop with a valve and a controller on the boiler, or the circulator pump would handle recirculating the water through water storage type loop when the controller determined the water was too hot in the boiler.

I'm wondering if that controller or valve isn't working properly?
 
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Old 11-09-07, 08:50 PM
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Valves?

Since the pipes are only getting hot 2 feet from the boiler, it makes me think there is some kind of blockage. This blockage could be a manual valve or an electic zone valve. Most wood fired boilers use a "normally open" zone valve. Has anyone replaced any zone valves? If so, maybe they used the wrong ones.
 
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Old 11-13-07, 06:46 AM
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Thumbs up

My issue is fixed.

A lot of you came pretty close to the problem....and I think one hit it on the head. The main issue was my lack of knowledge on this type of system. It turns out that in my rush to figure out why the system was increasing in pressure, I opened a valve that should remain closed if the wood furnace is to be used.

Once that was open, then the wood worked fine. Now as for the pressure issue: it turns out that all that was happening is that if my 3 zones stopped calling for heat, then the heat had nowhere to go and built up pressure in the lines.

The wood furnace is connected to my one zone that heats the entire downstairs. In order to keep the pressure incident from happening again I have to keep that zone on all the time, ie keep the thermostat cranked up. Then I just need to keep adjusting my fire to figure out just how hot I need to get it to keep the house comfortable compared to outside. For instance it was around 50 degrees the other day. This meant I only needed a very small fire...I figured that out when it got to 75 in the house.

It's a pain, but it's cheaper than oil!

I was told (my local oil furnance guy informed me of everything above) that I could install some type of heat coil thing that would transfer the excess heat away from the furnance when the thermostat wasn't calling for heat anymore. But the cost of it came close to $1000, so I'll wait on that.

Thank you for all your help. I love this site.
 
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Old 11-13-07, 08:37 PM
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Originally Posted by Kritheon
I was told (my local oil furnance guy informed me of everything above) that I could install some type of heat coil thing that would transfer the excess heat away from the furnance when the thermostat wasn't calling for heat anymore. .
I usually call them WINDOWS !!

Glad you got it sussed !
 
 

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