I suspect my Hot Water Baseboard pipes are leaking under concrete slab

foltzg · February 22

My House is 65 years old with 3 zone HW baseboard heat. I had the boiler replaced 7 years ago. Recently, I've been getting a LOT of air in the system. I've had to purge it periodically, but it's been getting to the point that I need to put a LOT of water into it every other day. Sometimes every day.

The bedroom and living room zones show no signs of leaks. (No visible leaks. No stains on wallboard ceilings, etc). I can only assume that this much water (have to purge it for 10-15 minutes per zone to get most of the air out), could be leaking under the ground floor slab. The piping for the lower ground floor zone is embedded in the concrete and pops up in 3 places to feed 3 Slim Line baseboard heaters.

The expansion tank appears to be okay but not sure how to test it other than tapping on it. (Top 60% sounds like it has water in it. Bottom 40% rings hollow-air). It has a Honeywell Super Vent above it.

We did have to dig up the family room (ground floor) 20 years ago to replace a main sewer pipe that rotted and collapsed under the floor as the dirt settled. Maybe the HW baseboard pipe has similarly collapsed?)

My only thought is to install a cutoff valve to isolate the ground floor zone and see if the leaking stops. Either that and/or hire a leak detection company to see if they can detect leaks. The ground floor is a combination of tile and LVT flooring over concrete.

Thoughts or recommendations?

Thank you,
Gene

hot_rod · February 22

A couple options, fill it to 12 psi, shut off the fill and observe the pressure drop. From hot to cold it should vary a few psi, but never drop to zero.

Be sure you don't leak out all the water and dry fire the boiler!

An infrared camera can help get a look at where the leak is. If you have access to one, if not Leak Detectors.com or others offer that service.

You don't really want to keep adding fresh water to the boiler, that will scale it up, quickly if you have hard water.

Jamie Hall · February 22

If you are putting in any water at all in a hot water system you may have a leak. At the rate you are adding water... you have at least one leak if not more.

Yes, isolating the under slab piping would be a good first step to try to eliminate where the problem is. It is most likely in the concrete somewhere, but don't totally eliminate the upper level piping just because you can't see the damage.

That's the beginning, however. You should also start thinking about how you are going to repipe the system if you find the buried piping to be the culprit.

clammy · February 22

As you suggest locate and isolate both supply and return for that zone . Usually a quick pressure test on that loop will reveal a leak . Personally I never waste the time in trying to locating the leak and trying to repair in a finished living area . I ll just figure out how to run it without ruining the space at least sheet rocks cheaper then cement and flooring . It s not all that uncommon a lot of bi level homes in my area where done w copper loops in the slab and they do go . The first signs are repeated air in upper loops that even after bleeding returns ,boiler water generally will come out orange due to the cast rusting from all the oxygen from make up water . The faster you isolate it the better chance you have of your boiler not be compromised by excessive make up water .
Peace and good luck clammy

foltzg · February 22

I will try shutting off the water input and seeing if the pressure drops much next week. It will be much warmer to try that.

As far a how to repipe the ground floor, I'm looking into where we can access walls and/or build soffits to run the new pipes. The ground level bathroom will be the trickiest part. New pipes will need a lot of 90 degree bends to get the pipe to/from the baseboards. Is that a problem?

Was also considering putting in a hydronic radiant heat floor (about 430 Sq ft total). Is that an option? Pro/Cons?

mattmia2 · February 22

You can run the new piping with oxygen barrier pex which can to some extent be fished through walls and ceilings. If you are going to go as far as a soffit you might as well just cut out a strip of drywall and drill through the joists.

Alan Welch · February 22

There is the possibility that the boiler is leaking and the water is leaving by way of the chimney.

hot_rod · February 22

If it makes pipe routing easier, you can site build radiant ceilings or radiant walls, fairly easily. Get heat and hide some pipes.

foltzg · February 23

Is there any possibility of my pressure regulator valve leaking air into the system? My neighbor said his boiler required daily filing and his plumber replaced the pressure valve and it solved his problem. I'm doubtful but it's better to ask than assume.

The boiler was installed in 2016.

Thoughts?

Gene

mattmia2 · February 23

Sounds more like your neighbor still has a leak and had a bad PRV as well. If you have an automatic air vent and no PRV to automatically add water then you might have to add water frequently for maybe a couple days to a week but it should stop after the air in the fresh water has worked its way out. If you continually have to add water it is leaving somewhere. Have you checked to see if the end of the pipe for the pressure relief valve is dry? What about the vent from the PRV if you have one?

Big Ed_4 · February 23

Right now , pump "Base Hit" into the system to seal the copper pipes to prevent further damage .

Then plan on replacing the lines that dip under the slab . Cover the new pipes with ArmorFlex , which they did not do back then....

pecmsg · February 24

foltzg said:
Is there any possibility of my pressure regulator valve leaking air into the system? My neighbor said his boiler required daily filing and his plumber replaced the pressure valve and it solved his problem. I'm doubtful but it's better to ask than assume.

The boiler was installed in 2016.

Thoughts?

Gene

Yes...................Close the inlet valve and find out. 24 hours should tell you.

Jamie Hall · February 24

Your friend's plumber did your friend no favours. If you are adding water, it is leaking out somewhere --n and doing that over time will ruin your boiler.

foltzg · February 26

Thank you everyone for your input and discussion. My plumber came Saturday morning and we've concluded that the amount of water needing to be replenished can only be from leaks of ground floor copper going through the concrete slab. He is going to schedule me for re-piping 2 of the 3 baseboard units through the walls & ceiling, while in the bathroom, the most difficult to reach, we will be replacing a slim line along the exterior wall with a kickspace heater under the vanity.

In the meantime, I was loosing so much water that I had to replenish daily and still had gurgles. I have now cut and capped the supply to the ground floor and no more gurgles. I have a thermometer in the furthest part, the bathroom and we're holding at 65 degrees in there with 30 degree temps outside. This will get me through to the plumbers schedule for the work.

Thank you all again for your great assistance.
Gene

I suspect my Hot Water Baseboard pipes are leaking under concrete slab

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