Pressure Loss in Lower-Level Radiant Heating Zone

chandlms

Hello, everyone! I recently purchased a home with a 10-year-old boiler (Weil-McClain Ultra) that has been maintained regularly. The house has three heating zones, including (Zone #3) in a finished lower level with radiant heating in the floor/ slab. After a recent service visit when the system was flushed, I've noticed that Zone #3 drops the system's pressure immediately and pretty dramatically (from 15psi down to 4-5psi). So for now I've closed the shutoff valves to this zone to maintain the desired 15psi in the rest of the house.

I've never had a boiler before and I'm new to all this, so I recorded this quick video to show you what I mean. Any ideas? The HVAC company that has serviced this system seems stumped. Thanks in advance for any pointers.

GroundUp

Pretty simple explanation, really. The 60 year old iron piping in the slab has begun to leak somewhere. Can you completely isolate each loop individually? This would help you narrow down which loop is the problem and allow you to either attempt a repair or just leave that loop isolated

hot_rod

With those v alves and unions you could isolate the loops and determine which one or ones are leaking.
I'd get a plan B in mind as it's rare to have just one leak in a 50 year old steel pipe system, time is not on your side with this one.

chandlms

Thanks for the perspective! I was guessing this might be pipes not full of water and that the pressure might build back up as they filled again, but we left that zone open for quite a while and the pressure didn't seem to be climbing much at all. Then of course I was concerned about water leaking into the slab, although I never saw evidence of water anywhere.

Will I be able to isolate those five loops simply by opening one valve at a time on the pipes going into the floor, without shutoffs on the return lines in the loop?

HomerJSmith

You're between a rock and a hard place. Is the leak is in the threaded connection or a hole in the pipe? If it is a hole in the pipe, there is, maybe, serious degradation in all the loops. I guess it all depends on how fast the pressure drops. A rapid drop would indicate a hole. However, if the system was recently drained there could be air in the pipes which would drop the pressure.

All you can do is abandon the leaking loop with shut off valves. If you could isolate the loop and fill it with air and check the pressure you would know for sure.

chandlms

I don't know where any leak might be (or not). The very rapid, almost immediate drop in pressure scared me and made me think "hole," too, but last winter this zone was operating and I don't think we had a pressure issue (although I didn't look at the boiler meter, specifically, we never had any heating issues in the house). That made me think that maybe something from the last maintenance (with a flush) created this issue somehow.

Thanks for all the help. This is over my head, in case you can't already tell!

Solid_Fuel_Man

I'm going to say that a 1950s iron system with no insulation under the slab (had not been invented yet!) Is costing you a lot to operate anyway. 

You can isolate the leaking loop, but you still have the others which are likely not far away form leaking as well. 

Only way to pinpoint the leak is to operate the slab (crank the thermostat) and have a look at the floor with a thermal camera. They are about $100 on Amazon for your smartphone. A leak will show up (usually) as a blotch whereas the rest of the piping will be straight lines.....

Now once you find the leak, what do you do with it? Chip up concrete, but its threaded iron pipe. Only real option is to weld/braze it. And that's not a good option really. Modern day pex is easily repairable right at the leak point, threaded iron....not so much. 

Sorry to be the bearer of bad news

bburd

The usual solution for leaking floor coils is to install baseboard (or other) radiators. 

chandlms

Not sure if this added information helps at all, but I just went down and opened the supply valves (just before and after the Zone 3 pump) while all five valves going into the floor were off. When I opened (what I think is) the return valve (see circled in photo), that's when the pressure dropped significantly. I closed the valves again before I took this photo and the pressure returned to the system pretty quickly.

hot_rod

A leak test could be fairly simple, break all the unions and lifts the header up. Build a pressure gauge setup,to connect to the union or pipe thread below, turn off the valve. So no you can test every loop, abandon the leaker,
Rust never sleeps, however.

HomerJSmith

Open the pump supply valves (yellow handles), keep the return valve off, close all the supply valves (green handles?), then...

Open one supply valve (green handle) at a time and look for a pressure drop, then close it and go to the next one.

The one with the pressure drop is the leaky one. If there isn't any pressure drop in any of them, the problem is in the return line between the shut off valve and the boiler.

GroundUp

HomerJSmith said:

Open the pump supply valves (yellow handles), keep the return valve off, close all the supply valves (green handles?), then...

Open one supply valve (green handle) at a time and look for a pressure drop, then close it and go to the next one.

The one with the pressure drop is the leaky one. If there isn't any pressure drop in any of them, the problem is in the return line between the shut off valve and the boiler.

There are no valves on the individual return loops, they're all tied together. That will not work.

HomerJSmith

Duh! Got it.