Hydronic Low Water Cutoff Issue

Equito · Mar 9, 2009

Problem: (system particulars below) In zoned system, first floor is heated w/in-slab tubes, upstairs by baseboard radiators (normally not run as we don't use the second floor for much). Unless air is periodically removed from system by running upstairs baseboard radiators, low water cutoff shows a yellow warning light and cuts blower off while tank gets up to temperature. It will restart quickly, run a few seconds, then get cut off again, and repeats this until the tank is up to temp.

The problem started after the system had been in place for several years. Low water cut-off is mounted high so light cannot be seen when standing, unless you're elevated or unless you put a finger behind the light and get the reflected glow. First two techs replaced the Aquastat which seemed to work for a while, though at great expense.

Third tech was about to replace the Aquastat and happened to see the Low Water Cut-off light. He suggested bleeding the air from the system by running the upstairs zones (normally closed) and that worked. He had no suggestions for why this needed to be done or why the air was accumulating in the closed zones, or how the problem could be prevented.

At this point, we have to run the upstairs zones for an hour or so every 2-3 weeks (when we notice the system clicking on/off).

Anyone know of a firm fix for this issue? Is something waterlogged (e.g. the expansion tank)? System particulars below. Any info appreciated.

System (11 years old):

Buderus Boiler G115 w/Becker blower, on top of integrated Buderus hot water heater

Amtrol Extrol Expansion Tank for Hydronic Heat Systems, Model 30 (pre-charge 12 psi, max 100 psi, temp max 240)

Honeywell Aquasat (3-4 years old)

JoDU · Mar 9, 2009

do u have zone valves or pumps and is the boiler actually low on water? Have they ever pulled the low water cutout ot see if its plugged or dirty

Equito · Mar 9, 2009

JoDU said:
do u have zone valves or pumps and is the boiler actually low on water? Have they ever pulled the low water cutout ot see if its plugged or dirty

1. Zone Valves - Yes - there are thermostat-activated valves for the larger zones, and the zones downstairs (slab tubes) have individual twist on/off valves to regulate the zones more specifically. We've never messed with those valves, and the thermostats are functioning. There are 3 pumps.

2. Boiler Water Level - So far as I know, the techs did not check it, and I do not know how to check it (but would like to, but also don't want to run afoul of the "No DIY" policy). One tech did say, "if the system was low on water, the Low Water Cutout light would not go out."

3. Pulling Low Water Cutout - So far as I know, the techs did not pull the Cutout to check it. Again, I be happy to, but don't know how. All I know for sure is that running the upstairs zones temporarily cures the problem (Low Water light goes out).

4. There are 3 BB tubes upstairs, each has a vent, one of them has a screw-on top that was allowing a small amount of water to burble out around the top (not out the appropriate vent hole), suggesting that air could be being sucked into the system.

Perhaps you could point me to some form of manual or other resource for performing these checks? And where I could get replacement vents. Thanks for your questions - they're helpful.

pacnw · Mar 10, 2009

pictures of the boiler showing the location of the controls, pumps, etc.

firecontrol · Mar 10, 2009

What information can you give on the type of tubing that was used for the infloor heating on the main floor? Brand? Any markings/specs printed on it?

snupytcb · Mar 10, 2009

Equito said:
Problem: (system particulars below) In zoned system, first floor is heated w/in-slab tubes, upstairs by baseboard radiators (normally not run as we don't use the second floor for much). Unless air is periodically removed from system by running upstairs baseboard radiators, low water cutoff shows a yellow warning light and cuts blower off while tank gets up to temperature. It will restart quickly, run a few seconds, then get cut off again, and repeats this until the tank is up to temp.

The problem started after the system had been in place for several years. Low water cut-off is mounted high so light cannot be seen when standing, unless you're elevated or unless you put a finger behind the light and get the reflected glow. First two techs replaced the Aquastat which seemed to work for a while, though at great expense.

Third tech was about to replace the Aquastat and happened to see the Low Water Cut-off light. He suggested bleeding the air from the system by running the upstairs zones (normally closed) and that worked. He had no suggestions for why this needed to be done or why the air was accumulating in the closed zones, or how the problem could be prevented.

At this point, we have to run the upstairs zones for an hour or so every 2-3 weeks (when we notice the system clicking on/off).

Anyone know of a firm fix for this issue? Is something waterlogged (e.g. the expansion tank)? System particulars below. Any info appreciated.

System (11 years old):

Buderus Boiler G115 w/Becker blower, on top of integrated Buderus hot water heater

Amtrol Extrol Expansion Tank for Hydronic Heat Systems, Model 30 (pre-charge 12 psi, max 100 psi, temp max 240)

Honeywell Aquasat (3-4 years old)

did they use tape or pipe dope on the threads? sometimes tape will rip and cause a screwy situation with the ground. i have had this happen a few times.

cehs · Mar 10, 2009

If you have a combination of galvanized/steel pipes and copper, you can get electrolosis between the pipes (like a battery).
Mineral salts in the water which normaly corrode pipes, then act like an electrolyte and the water in the system decomposes into hydrogen forming vapors in the system...

Equito · Mar 10, 2009

Here are some pics of the very tight install.

1. The pipes in the slab are copper, but that's all I know about them.

2. I can see tape on some of the joints (bigger pipes).

3. I checked the air purge valves on the upstairs baseboards. All but one have a recessed slot in the top (photo 2396, below), and the remaining one (photo 2392, below) looks like a Hygrometer-style (larger screw-on top that also has a slot, though more flush with the top).

The Hygrometer-style leaked a little water around the top (beneath the top ring), but not out the bleed hole, when I rocked it with finger pressure. I tightened up the top ring and it stopped. Not sure if there are those fiber disks in there, or not.

Thanks for the input.

beenthere · Mar 10, 2009

The air eliminator is probably dirty, and not working.

And they left no room to get to it and clean it.

Equito · Mar 10, 2009

beenthere said:
The air eliminator is probably dirty, and not working.

And they left no room to get to it and clean it.

1. Is the air eliminator the vent thing seen in the 6th pic down, just to the right side of the red cutoff valve that has a pipe coming from the bottom and going over to the Extrol unit?

That vent is where the air comes out once you run the upstairs baseboards.

If the air eliminator is somewhere else, please let me know where it's likely to be, and what it looks like, as the wall to the left of the unit is removeable and I may be able to get to it.

Thx

beenthere · Mar 10, 2009

That would be the air eliminator.

ascj · Mar 10, 2009

Copper in the slab may be leaking. You constantly are requiring make up water, which is bringing oxygen. The spirovent in either dirty or clogged. The baseboard returns coming off the top of the return, provide a nice place for the oxygen to go. Also for your picture, I can't see how the mixing valve or diverter valves is able to work properly, piped that way.

If you are purging air, then where is it coming from. Best guess, the make up water from a leak or leaks in the slab.

Equito · Mar 11, 2009

ascj said:
Copper in the slab may be leaking. You constantly are requiring make up water, which is bringing oxygen. The spirovent in either dirty or clogged. The baseboard returns coming off the top of the return, provide a nice place for the oxygen to go. Also for your picture, I can't see how the mixing valve or diverter valves is able to work properly, piped that way.

If you are purging air, then where is it coming from. Best guess, the make up water from a leak or leaks in the slab.

I like the sound of "your baseboard air purge vents are allowing air into the system and need to be replaced" a WHOLE lot better than "your slab-bound copper tubes are leaking."

The main vent does let air out (you can hear it), but only when the upstairs is brought into play.

If there was a leak in the slab tubes requiring water to be replaced, why wouldn't the make-up system just do it on its own, without the upstairs baseboards being activated? It seems the make-up system would prevent the Low Water Cut-off from activating and killing the burner.

If the make-up system isn't functioning normally, then why would it do so when the baseboards are activated?

I'm starting to understand the complexities of this system, so that's a start. I just want to have an efficient conversation with my tech, so this is all good info.

ascj · Mar 11, 2009

Equito said:
I like the sound of "your baseboard air purge vents are allowing air into the system and need to be replaced" a WHOLE lot better than "your slab-bound copper tubes are leaking."

The main vent does let air out (you can hear it), but only when the upstairs is brought into play.

If there was a leak in the slab tubes requiring water to be replaced, why wouldn't the make-up system just do it on its own, without the upstairs baseboards being activated? It seems the make-up system would prevent the Low Water Cut-off from activating and killing the burner.

If the make-up system isn't functioning normally, then why would it do so when the baseboards are activated?

I'm starting to understand the complexities of this system, so that's a start. I just want to have an efficient conversation with my tech, so this is all good info.

Let's say you have 12psi in you system. That gives you 27.72 feet of head. Unless those baseboard tee's are high than that and leaking, you won't suck air.

What i'm saying is your getting air in the system. Unless any components is above 28 feet, assuming your system is at 12psi or greater, you are going to leak water not suck air into the system. So the only other way air gets in the system is from makeup water or osmosis through the walls of the non ferrous components of the system. With half way descent air elimanator the osmosis is no problem. But with sustain makeup water, lots of time the air elimanation can't keep up. The oxygen will go to the highest point of the system. If that highest point of the system isn't run through the air elimination it will slow act like a air custion and prevent the water regulator from filling, hence the pressure is ok.

I hope you are following this. lol

Equito · Mar 11, 2009

ascj said:
Let's say you have 12psi in you system. That gives you 27.72 feet of head. Unless those baseboard tee's are high than that and leaking, you won't suck air.

What i'm saying is your getting air in the system. Unless any components is above 28 feet, assuming your system is at 12psi or greater, you are going to leak water not suck air into the system. So the only other way air gets in the system is from makeup water or osmosis through the walls of the non ferrous components of the system. With half way descent air elimanator the osmosis is no problem. But with sustain makeup water, lots of time the air elimanation can't keep up. The oxygen will go to the highest point of the system. If that highest point of the system isn't run through the air elimination it will slow act like a air custion and prevent the water regulator from filling, hence the pressure is ok.

I hope you are following this. lol

Except for the "feet of head" construct, I think I understood all of that. Thanks. While the BB ts are not 27 feet higher than the furnace, they are about 6 ft higher, and 20-40 feet away from the furnace - but whether that makes a difference, I don't know.

The system seems to maintain 18-20 psi at rest, and pops to 21-22 while operating. Right now, for example, the burner/pump have been off almost an hour, the boiler's at 130 F. and the pressure's at 20.5. If it doesn't seem to ever drop anywhere near 12 psi, never mind below it, does that suggest there is no leak? Or only that the make-up system is keeping the psi up?

The most knowledgeable tech (the one that figured out that running the upstairs baseboards would flush out the air and stop the Low Water Cut-off from cycling the burner on/off) had a light bulb go off when he heard we hardly ever used the upstairs baseboard heaters. In his opinion, the simple lack of use caused the condition, and not some defect in the system. He didn't seem to think it was unusual, in other words.

I appreciate the explanation and input. Any new thoughts are appreciated.

beenthere · Mar 11, 2009

Air is getting into your system, some how.
And not using the upstairs, isn't causing you to have air issues at the boiler.

Tell them to do a proper check on your expansion tank.

ascj · Mar 11, 2009

As Beenthere stated, lack of use doesn't cause air to accumilate in the system. With the pressures you stated, there is also, no way of the system to suck air through a leak. So the only thing I can see, is there is a leak you can't see, that is bringing in an excessive about of makeup water(oxygen bound) in a system that can't get rid of it. And from the pictures, it looks like the only place you can't see a leak is the concrete floor tubing. Does concrete causing copper to leak, NO. But some ingredients in the concrete can. Also when tubing can't expand properly, it with cause leaks.

fenian · Mar 11, 2009

i thought the extrols were supposed to be mounted upright. anyone know if that's the case?

ascj · Mar 11, 2009

fenian said:
i thought the extrols were supposed to be mounted upright. anyone know if that's the case?

I have never heard that. The only issue I have found with them mounted horizontally, is it puts alot of stress at the 1/2" coneection without the tank being supported properly.

firecontrol · Mar 12, 2009

Extrols should be mounted with their connection pointed up. By positioning the tank in this way any air that might get to the tank will migrate back out to the system and be expelled as it should be.

With an automatic water make up any leak that might be in the system will not show up, because as soon as any water leaks out it's replaced with fresh water.

Only system I ever saw that "generated" it's own air/gas was an aluminum block boiler that had improper antifreeze installed in the system. Something in the makeup of the antifreeze was interacting with the aluminum and was creating a gas inside the system. I don't believe your system contains anything that would cause this.

The other conditions that can cause air to become loose in an otherwise sealed system is actual boiling of the water in the boiler itself. This can be caused by low water flow through the boiler, not enough pressure being maintained (don't always believe what the pressure guage says) or blocked passages can cause to much heat/btu's to be delivered to the water side (in small concentrated areas) causing the temperature of the metal in contact with the water to cause surface boiling even at correct pressures.

Air isn't magic. It's either being generated, interjected or pulled into the system. Trick is finding out which.

Hydronic Low Water Cutoff Issue

Equito

JoDU

Equito

pacnw

firecontrol

snupytcb

cehs

Equito

beenthere

Equito

beenthere

ascj

Equito

ascj

Equito

beenthere

ascj

fenian

ascj

firecontrol

Top Contributors this Month

Recommended Communities