Eichler Slab Leaks: Is It the Radiant Heat or the Water Line?

Why do Eichlers leak under the floor?

An Eichler has no crawlspace and no attic. The house sits on a concrete slab and the ceiling is the underside of the roof, so the pipes a conventional house hides under the floor or overhead run through or under the slab instead. Two separate systems live down there: the supply lines that carry your drinking water, and the radiant tubing that heats the house.

The Eichler Network sums up how radiant lines fail: corrosion, the slab cracking and shearing a pipe, or someone drilling into the floor and hitting one. Supply lines in a slab leak for their own reasons, and the repair choices for the two systems are different, so the first job is working out which one has the problem.

Is it the radiant heat or the water line?

Most radiant leaks never show on the floor, and the system is built in a way that hides them. The loop is supposed to be sealed, and when it loses water, a fill valve tops it up from your supply line to hold pressure. The Eichler Network radiant heating guide puts normal operating pressure at 10 to 20 psi, and warns that every refill brings in fresh water with oxygen in it, which speeds up corrosion in the pipe.

That refill is also why a meter test alone can fool you. A leaking radiant loop draws from the same supply as your faucets, so the meter moves either way. Separate the two first. With the heat off:

1. Close the fill valve that feeds water into the radiant boiler.
2. Turn off every faucet, toilet, and appliance, and watch the water meter. If it still moves, the leak is on the drinking water side. Our water bill leak guide walks through reading the meter.
3. Write down the boiler pressure, then check it at the same time each day for two days. If it keeps dropping with the fill valve closed, the radiant tubing is losing water.

Other clues show up around the house: a patch of floor that feels hot with the heat off, the sound of water running when everything is shut, new cracks in the slab, a water bill that jumped, and a white powdery crust on the outside of a wall near the ground.

Steel or copper? Check the manifold with a magnet

Eichler did not use one material the whole time. According to the Eichler Network, the radiant tubing was copper in the early 1950s, switched to steel during the shortages of the Korean War, and went back to copper later in the decade. That switch overlaps the years Marin's first Eichler tracts went up, so the only way to know what is in your floor is to check.

The test takes ten seconds. Hold a magnet against the radiant manifold, the cluster of pipes where the heating loops come together near the boiler. If it sticks, the tubing is steel.

That answer shapes every decision after it. The Eichler Network notes that most leaking copper radiant tubing can be repaired. With steel, the first leak can mean the system is near the end of its life, because the corrosion that caused it tends to be spread through the pipe.

How do you find the leak without tearing up the floor?

Whatever sits on top of the slab has to come up and go back down at every spot we open, so the goal is one small opening in the right place. We isolate and pressure test each line to confirm which one is losing water, narrow it down with acoustic listening equipment, and on hot lines use a thermal camera, which shows a leaking hot water line as a warm streak across the floor. Only then does the saw come out.

Repair it in the slab, reroute it, or abandon it?

For a drinking water line, a spot repair through the slab makes sense when the rest of the pipe is sound and the leak is somewhere reachable. Once a line has leaked and the rest of it is the same age, rerouting usually wins, and in an Eichler that means over the roof or along the outside walls, since there is no attic or crawlspace to use. If a reroof is coming, that is the time to do it: new line can run in a sleeve under foam roofing so it can be pulled and replaced later. Our repipe page covers copper and PEX.

For radiant tubing, copper usually gets repaired. Steel is a harder call, and once it has started leaking in more than one place, abandoning the slab loop and heating the house another way is often the honest answer. That is a heating decision as much as a plumbing one, and we will tell you where our part of it ends. If water is coming up through the floor right now, our emergency line is open every day.