How to repair damaged underfloor heating pipe

Clients and builders often ask me “What happens if an underfloor heating pipe gets damaged during construction?”

As a general rule, to avoid the pipe getting damaged at all we make sure that all pipes run through doorways and not under walls. That way nobody needs to drill into the concrete where the pipes are. But sometimes accidents happen.

When we install an underfloor heating system, we fill the pipework with water and leave the system pressurised. A pressure gauge on the manifold shows us that the water pressure in the system is above atmospheric pressure like the the photo below. If somebody punctures a pipe, the pressurised water will leak out immediately so that they know what’s happened. When that happens, the pressure gauge on the manifold will drop to zero.



If a pipe in the concrete slab gets damaged, this is how we fix it.


Step 1 – Oops!

Somebody has drilled through our pipe!



The first thing to do is to expose the pipe so we can see the extent of the damage by chiselling away the surrounding concrete with a jackhammer.


Step 2 – Cut out the damaged section

We’ll start by cutting out the damaged section of with a PEX cutter.

We want to cut out the smallest section of pipe that we can, but large enough to get rid of all the damage.



Step 3 – Prepare the pipe

Next we have to ream the ends of the pipe with a pipe reamer to get smooth edges. This allows our fitting to form a tight seal on the end of the pipe.



The reamer cuts a smooth edge onto the end of the pipe, ready for a fitting.




Step 4 – Cut a section of clean pipe

The next step is to cut a section of fresh PEX pipe to replace the section that we cut out. If the damaged section was only small, then we might be able to repair it with a single fitting. If it’s too long then we need a new section of pipe.



In this case, the damaged section was long enough that we need to cut some extra pipe to make the join. The new section of pipe needs to be long enough to replace the length we removed, but short enough to allow the fitting at either end. This requires a bit of careful trial and error.



Step 5 – Attach fittings

First we push the nuts over the end of pipe, then push the olives and fittings onto the end of the pipe.

We do the same with the replacement section of pipe which will fit into the middle.



Then we can screw the nuts onto the bushes to join the fittings together.

Here the fittings are in place and we’re ready to screw on the last nut.



The last fitting is usually tricky to get into place but the plastic pipe is a bit flexible so there’s some room to manipulate it. If there’s not enough flexibility in the pipe within the small space, we might need to chisel out some more concrete.

The O-rings won’t seal unless they’re properly seated. Sometimes when we’re manipulating the fittings in these tight spaces, the O-rings can get pinched in the fittings. We need to check that hasn’t happened.



Step 6 – Tighten

We need to tighten the nuts with a spanner and plumbers’ grips.




Step 7 – Pressure Test

The next step is to pressure test the new fitting to make sure it’s properly sealed. We have to refill the underfloor pipework with water at the manifold and check that it’s holding pressure.




Step 8 – Seal

It’s good practice to wrap the repaired fitting in a layer of waterproof tape. This keeps the concrete off the metal, which helps prevent any corrosion.


Now we’re ready to fill in the concrete and get back to building!