Hydronic Low Water Cutoff Issue
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)
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.
Originally Posted by JoDU
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.
Last edited by Equito; 03-09-2009 at 08:32 PM.
pictures of the boiler showing the location of the controls, pumps, etc.
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?
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.
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.
Originally Posted by Equito
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...
Those who dance, appear insane to those who do not hear the music.
Those who believe, appear ignorant to those who do not know God.
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.
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?
Originally Posted by beenthere
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.
That would be the air eliminator.
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."
Originally Posted by ascj
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.