Radiant heat only circulating in 1 of 3 zones

joe999

I've got a problem with my radiant heating system where it will only circulate in the upstairs zone. I have tried several other forums without success. I'll try to keep it concise:

It's a SlantFin system, installed in '86. Here are pics of the whole system:
http://www.imageno.com/tuee6ygavshnpic.html
http://www.imageno.com/n3hicq2i0tctpic.html
http://www.imageno.com/6tit7ul0g3wipic.html

And the floorboard radiators:
http://www.imageno.com/eg91ehpx09qlpic.html
http://www.imageno.com/aljzfinby010pic.html

To sum up the issue, all 3 zone thermostats are working and turning on their corresponding Honeywell Synchron valves. The boiler heats up just fine. The upstairs zone warms up when the upstairs thermostat commands the corresponding Synchron to open. The problem is that when the downstairs thermostats command their corresponding Synchrons to open, I get no flow to either one.

Manually opening the valves do nothing either. The boiler is hot, and even with the zone valves manually opened, there is no flow. It was suggested that I have air in the downstairs zones, and to install valves in the returns. The problem there is that the supply to the system is on the return side. I have drawn a picture to illustrate it:
http://www.imageno.com/x4l7sf0evy9tpic.html

There is only one outlet in the system (the blue spigot at the boiler return), so I can't create a pressure differential to bleed the system. I have opened up the little "hygroscopic disc" bleeder valves all over the house, and I only get water out of them. The only way I can see to bleed this thing is to open up the little valves, then flip the lever on the pressure regulating valve and let water spray all over the house!

Does anyone have any ideas? Or could it be something other than air in the system? It is acting like there is some hidden shutoff valve to the bottom 2 zones that is not letting anything flow. I would think if there was air in the system, I would still get a little bit of flow, but I am getting absolutely no heat at the bottom 2 zones. Thanks!

sonofaplumber

Looks like you have plenty of bleeders and shutoffs to get any air out of the system. This may be more of a flow problem than an air problem.

First I'd try to bleed the zones backwards where the feed is on the return. I'd close all the shutoffs before your zone valves (synchrons), close the shutoffs on 2 of the returns and bleed the remaining 3rd zone by opening the system feed and the bleeder on the feed side. I know its confusing I hope I didn't lose you.

Are you having this issue only when the upstairs is calling for heat? with one circulator it is common to only have heat upstairs when both are calling because that's the route the water wants to take. Try closing all the manual shut offs except one downstairs zone and see if you get any heat from it, I bet you will.

sonofaplumber

Also if you do isolate a downstairs zone and it is air locked, you could have dangerous situation when the burner fires.

The boiler will get real hot real fast. Watch the temp gauge and if you get above 200* open the upstairs zone back up and manually open the zone valve quickly to send the heat away from the boiler.

Otherwise your relief valve could pop off and that can be alarming.

joe999

I think I'm following what you are saying....to block off the "supply" valves near the synchrons, and 2 of the return valves. But shouldn't I open the bleeder on the supply side since the feed is on the return side? If I open the bleeder on the feed side (return to boiler), the water is just going to go like 2 feet like shown by the short blue line in the picture I drew:
http://www.imageno.com/x4l7sf0evy9tpic.html

And no, the issue isn't only when the upstairs is calling for heat. I can have the boiler ready to go with the upstairs off, and manually open the synchron to either bottom zone, and no heat. The boiler is behaving normal - it slowly heats up to about 180 degrees then shuts off.

sonofaplumber

Okay so when you bleed make sure the the boiler and circulator is off otherwise it would fight you (your reversing the flow) and you could overheat. Just hit the service switch.

I mean open the bleeder closest to the zone valve so the water has to go backwards all the way through the downstairs to get to the bleeder from the 'cold' side of the boiler.

joe999

Deleted/updated last post:

I found a bleeder on one of the radiators on the far side of the house with a good clean 2" hole in the concrete around the copper pipe, which allowed me to just let the water flow down in to the ground. Yes, I know that is probably a bad idea with cold weather coming up, but I'm desperate to figure this out.

I turned on the heat, made sure the boiler was warmed up, and closed the return valve to that zone to ensure the water that was coming out was coming from the boiler and not the cold supply line. I let it sit for a good hour with the bleed fully open, and still just cold water was coming out. That leads me to believe that it is definitely a flow problem. Am I right in assuming that is one of 2 problems - air in the system or a partial blockage?

Or could the circulator pump be dead? Like some strange phenomenon where the upstairs works due to rising hot water and gravity, and the downstairs need a circulation pump??

joe999

I don't know what I did, but all zones are working. I went around and re-bled a few random valve locations. I had went around and bled them all last night, so I don't know what the difference was. However, somehow, when I was messing with one of the valves, I heard the radiator start to crackle and the water started flowing. My only guess is that I "nudged" the water along somehow, and once the water was flowing, the air scoop started taking extra air out of the system?? I really don't like it when things start working and you don't know why.

I'm going to replace all the bleeder valves, because those ones are very difficult to get to shut off once you crack them open. These ones were suggested on another site:

http://www.supplyhouse.com/Webstone-41685-1-8-FIP-x-MIP-Full-Port-Forged-Brass-Mini-Ball-Valve?gclid=CKH7jczsycgCFQwXHwodCEgCLA

In any case, thanks for all the help!

SWEI

You might consider these instead. Manual vent plus a hygroscopic auto vent and includes a check valve -- so you can replace the hygroscopic element without depressurizing the system.

joe999

SWEI,

I'm open to suggestions, but in the several forums I've been on with this problem, I've found a lot of disdain for the hydroscopic valves. They seem to not exactly work as advertised (based on word of mouth, and what I've seen on my system), and those ones you sent look like they have a plastic cover. The ones I have on there right now, I had to use a set of giant Channel Locks just to get them open and shut. My concern with a plastic valve would be a few years down the road, them breaking/cracking, and having to replace them all over again. It seems like having a good old-fashioned 90 degree ball valve, where I can put a 180 degree elbow and definitively drain the water into a cup (rather than just squirting all over) would be the way to go. Have you or anyone else had good/bad experiences with these hydroscopic valves? Do they work so well that you would never have to use pliers on them?

hot_rod

Ideally with a hygroscopic, you don't need to open and close them. Install the vent, manually bleed the first time, then leave in the auto position, no need to wrench anything.

At some point the system should be air free and all the vents take a break. if you have chronic air, look for places that it is entering the system.

Also check the fill pressure, and adjust so you have 5 psi at the highest point in the system. Adjust the expansion tank pre-charge if you add fill pressure.

Is the pump circulating away from the expansion tank/ That alone can solve a problematic air problem.

What kind of flow rate, if you are flowing below 2 fps, it can be tough to get all the air back to the air purger near the boiler, especially with vertical piping, air rises up through the fluid at lazy flow rates.

If you have a multiple speed circulator, try bumping up a notch.

With a good micro bubble purger installed at the boiler supply, pumping away, and adequate fill pressure and flow rate you really should not need any of those manual air vents scattered around the home.

SWEI

joe999 said:

My concern with a plastic valve would be a few years down the road, them breaking/cracking, and having to replace them all over again.

The valve bodies are chrome-plated brass. The plastic portion screws in and seals with an O-ring. We're installing some in an old gravity system later this week. Plenty of rust and gunk in there so we'll see how they fare.