Does a cold spot in underfloor heating mean there is a leak?

Usually not. The common causes are trapped air, an actuator stuck closed on the manifold, or sludge in the loop, and none of those lose water. The test that tells them apart is the pressure gauge: note it, wait a day without topping up, and read it again. Steady pressure means it is not a leak.

Can you find an underfloor heating leak without digging up the floor?

That is the normal way to do it. A pressure test confirms the loss is real, thermal imaging maps the loops and shows where the pattern breaks, and tracer gas finds the pipe itself through screed and concrete. The floor is then opened at one place rather than explored.

Why should I stop topping up the pressure?

Because every top-up feeds the leak. It also removes the only symptom that would have let anyone size the loss, and the water goes under the floor, into the screed and into the joists. Topping up daily is the single most expensive habit on a heating leak.

My whole underfloor system is cold, not just one part. Is that different?

Yes, and it is usually simpler. If nothing is warm, the fault is generally upstream of the manifold — the pump, the zone valve, the blending valve or the boiler not firing for that zone — rather than in the buried pipework.

Parts of my underfloor heating are cold

Do this first

Write down the system pressure, then leave it alone for 24 hours and read it again. Do not top it up in between. That single number separates a leak from everything else on this page, and it is the one piece of information most people skip.
Feel the flow and return for each loop at the manifold. A loop that is hot on the flow and cold on the return is circulating badly. A loop cold on both is not circulating at all.
Look at the flowmeters. The little sight gauges on the manifold should all be showing flow. One sitting at zero tells you which loop to work on.
Check the actuators. These are the small electrical heads on the manifold that open each loop. They stick closed, and it is extremely common. Pull the head off: if the pin underneath springs freely and the loop starts to warm within twenty minutes, the actuator is the fault.
Check the room thermostat is actually calling. A zone that is not asking for heat behaves exactly like a zone that is blocked.

The fork that matters

Pressure steady, one loop cold. Air, a stuck actuator, or a flowmeter that has been wound shut. Not a leak.
Pressure steady, every loop cold. Look upstream of the manifold — the circulating pump, the zone valve, the blending valve, or a boiler that is not firing for that zone. Not a leak.
Pressure dropping, and a warm or damp patch on the floor. Stop topping it up and treat it as a leak. Every top-up puts more water under the floor and makes the damage worse while hiding the symptom that would have found it.

Air, which is the usual answer

Underfloor loops are long, flat and buried, so air that would burp harmlessly out of a radiator sits in a high point in a screed floor and stops the circuit dead. The fix is not bleeding a radiator — it is flushing loop by loop at the manifold, closing every circuit except the one being cleared and pushing water through it to a drain until it runs without bubbles. Done properly it is an hour's work and it does not come back.

Sludge, which is the second answer

Magnetite is a fine black iron oxide that forms in any system with steel in it. In a radiator it collects at the bottom and gives you a cold strip; in an underfloor loop it settles along the flattest run and chokes it. Systems over about fifteen years old, or any system that has been drained and refilled without inhibitor, are the candidates. A chemical clean and fresh inhibitor is the fix, and a magnetic filter is what stops you doing it twice.

When it genuinely is a leak

A buried pipe leaking into screed does eventually show as a cold spot, because the loop cannot hold pressure and cannot circulate properly. What separates it from air is the pressure gauge falling, and often a patch of floor that is warm in the wrong place or a skirting board that has darkened. That is what tracer gas and thermal imaging are for: the pipe is found before the floor is opened, and the floor is opened once. We cover that on underfloor heating leaks and on a warm patch on the floor.

Frequently asked

Does a cold spot in underfloor heating mean there is a leak?: Usually not. The common causes are trapped air, an actuator stuck closed on the manifold, or sludge in the loop, and none of those lose water. The test that tells them apart is the pressure gauge: note it, wait a day without topping up, and read it again. Steady pressure means it is not a leak.
Can you find an underfloor heating leak without digging up the floor?: That is the normal way to do it. A pressure test confirms the loss is real, thermal imaging maps the loops and shows where the pattern breaks, and tracer gas finds the pipe itself through screed and concrete. The floor is then opened at one place rather than explored.
Why should I stop topping up the pressure?: Because every top-up feeds the leak. It also removes the only symptom that would have let anyone size the loss, and the water goes under the floor, into the screed and into the joists. Topping up daily is the single most expensive habit on a heating leak.
My whole underfloor system is cold, not just one part. Is that different?: Yes, and it is usually simpler. If nothing is warm, the fault is generally upstream of the manifold — the pump, the zone valve, the blending valve or the boiler not firing for that zone — rather than in the buried pipework.

No find, no fee · £150 per hour. The rate is fixed before we attend and does not rise for a difficult property, an awkward access or an evening visit. The total depends on how long the job takes; the rate cannot change.