Slab floor radiant heat might have a leak

[mike4244]

My in-laws’ summer house, which is walking distance from me (
 ) appears to have a leak in the hot water radiant system.  It was built in 1961 and is maybe 1500 SF, slab on grade, with what might be the original suitcase size boiler in an outside closet (no basement).  Single zone, with what I’m guessing is a balancing manifold in a hall closed with a bunch of valves with the knobs removed and copper tubing coming and going.

I check on it once a week or more, and found the heat not functioning, with the tiny pump running and making a weird pulsing sound (around 2 Hz).  Pilot was lit, but temperature gauge was low, and pressure gauge (single dual gauge unit) was down on the pin.  

I called the service guy with who they have a contract, and he said the water pressure was so low it cut out.  He let in some city water, did a quick check of systems, and all was well again.  Heat was still working the next day, and the indoor temp had come up to winter normal of 50F.

Check again today, and no heat (40F inside), pump motor was hot, and no pressure.  Not good.

I’ll have to ‘call the man’ again, but I’d like to know where the water is going, assuming it’s going somewhere.  If it’s leaking in the slab, how do they find it without breaking up the entire house slab and hoping for an early hit?  

I’d just like to know, though I’m not about to start tearing up their house looking for the leak.  How do they find a leak in a slab when no water is showing inside?

Neighbor has a summer home that had the same type of heat in the slab. He could see dampness on the floor. I lent him a Skillsaw with a diamond blade to cut the concrete. He said he replaced 3'-0" of copper pipe, left the trench open for several days to check for leaks.
He filled the trench with grout. Two years later he developed another leak in another room. He then called a plumbing outfit that suggested base board heat. I think that's what he went with, not positive because they moved.
Probably best to abandon the original system, fix one leak and expect more.
mike

[JosephP]

Obviously we don't have 70 years to look back on, but can PEX be expected to be more reliable than copper for in slab radiant heat??? I've been in several shops that were heated that way and it seems to make a lot of sense...unless it leaks!

[TDKPE]

FWIW, I warned them (sort of*) about slab floors and plumbing.  But what do I know?

I’ll go back later this morning to check on the heat and report back.

*My MIL, SisIL, and DW didn’t want me to say anything negative to my in-laws when I looked at the house, before my FIL saw it.  With that kind of army arranged in close proximity, armed to the teeth, it’s best to keep one’s mouth shut, though I did whisper a few warnings into my nearly deaf FIL’s ear.  But the die was cast, so there was no sense in stirring a hornet’s nest that I’d have to live near, and in, so that was that.  And here we are.

[TDKPE]

In normal operation, the water supply valve should be on.  The downstream regulator will lower the pressure to 12 psi as it enters the boiler loop.  There must be an expansion tank somewhere, too. 

<snip>

I don't know why the water supply valve is shut off unless the tech. decided that was better than having a flood somewhere.  But if he knew there was a leak you think he would have told you so.  

If it comes to a new heating system can you piggyback into the central AC system by adding a heat exchanger from the boiler or a heat pump?  If there is no central AC then how about a split mini system and heat pump?  

That’s what I thought about the feed water.  I grew up with cast iron radiators and nobody ever added water to the system that I was aware of, and I was pretty aware of the systems in that house.  We did have to drain the expansion tank once in a while, though, as it’s not a bladder type.  Neither is the well water tank.  

   

I don’t know why the valve is shut, either, but I’ll ask them.  There is an expansion tank, and it doesn’t look very old.  Looks like 2-3 gallons.  Probably works at least to some degree, as the pressure drops rather than rises to where it vents.  

There’s no central A/C and therefore no ducts.  So if they end up doing anything, it’ll have to be fix the leak(s), install baseboard fin-tube, install a warm air heating system in the attic, install a packaged unit outdoors with ducts to the attic, or mini splits, though that’s expensive.  And I don’t think they have a lot to spend at this point, after milking the equity out of their Florida home with a reverse mortgage.

So if the leak isn’t too bad, just doing nothing may be an option, especially since I’m the winter care taker, so it’s mostly on me.  

[Foggy]

I don't know a thing about it, but would some auto radiator stop leak work?

[JosephP]

I don't know a thing about it, but would some auto radiator stop leak work?

Does it work in a radiator?

[Snipe Hunter]

Does it work in a radiator?

Good point

[Snipe Hunter]

Single story? Attic?

Heat pump in the attic, insulated flex duct.

[TDKPE]

Went back yesterday morning (the next day), and pressure was down again.  So opened the feed water valve, and listened while the regulator allowed water in.  I didn't use the little manual fill lever on the regulator, as I wanted to know if it worked.

Quiet, but I could hear it.  And it stopped at somewhere around 12 psi, though it's hard to tell with the temperature/pressure gauge going all the way up to 90 psi.  
  Heat was working, though, as I caught it before it dropped enough to shut down.  Building temp was back to 50F, which is the set point.

I was wrong about the boiler age, though; it was new in 2001, per a sticker.  For some reason I thought it was much older.

FIL told me a service company checked the glycol about five years ago, and said it was 'not good', so they drained and refilled with some mix of water an glycol.  I don't know what about it was not good, but presumably the freeze protection was not low enough.  If this thing has been leaking slowly for years, the fresh water would dilute it over time to where it's mostly water.  This thing may have been leaking for years.

I'll keep an eye on it, but pressure is staying up with the fill valve doing its thing, and the heat is working, and warm weather is coming, so that's as good as it's going to get for the time being.  Just trying to keep the pipes from freezing, including the incoming city water and meter which is in the boiler room which is nothing more than a little closet with only one door to the outdoors. 

Last photo is the pressure gauge after running all day with the feed water active.

   

   

   

   

[TDKPE]

Single story? Attic?

Heat pump in the attic, insulated flex duct.

From above: 

That’s a possibility.  Very tiny attic, though.  Half the house has cathedral ceilings, the other has shallow attic.  But with the cathedral ceiling, there’s a ‘beam’ down the middle, and that could be built out with duct and registers and made to look (almost) like it belongs.

I don't think a heat pump will work here, as it gets too cold.  Though electric resistance elements would have to be used as backup.  And a heater put in the boiler room, since the water main will freeze if it isn't kept warm.  I did, once, when it went well below zero for a week a few years ago.