In-floor heating: a zone won't warm up

A single cold zone is usually something small and local — a setback on the thermostat, a tripped GFCI, or a pocket of air in one loop — not the whole floor system failing.

tuneWhat are you noticing?

Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.

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Start here

In Canadian homes, check the thermostat first. Turn it well up, make sure it isn't in a programmed setback, and confirm the floor-sensor mode is selected. On an electric floor, look for a tripped GFCI or test button on the thermostat and reset it once — a bumped setting or a single GFCI trip is the most common reason a zone goes cold, and it costs nothing to rule out. If the GFCI won't stay reset, stop and read the safety note.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order

Beginner-friendly Doable, with care Safety-critical Call a pro

visibilityHow to check the settings and GFCI

report A GFCI that won't reset is telling you somethingThe GFCI on an electric floor protects against a live-to-ground fault in a cable buried under the floor. Resetting it once is fine. If it trips again the moment you reset it, stop — the fault is real and forcing power to it risks shock and damage. This is not a homeowner repair; leave the circuit off and call a licensed electrician to locate the fault.

Turn the thermostat well above room temperature and check it isn't in a programmed setback or vacation mode; confirm it's set to sense the floor (floor or floor+air), not air only.
On an electric floor, look for a GFCI or a small test/reset button on the thermostat. If it has tripped, press reset once and watch it.
If the GFCI holds and the floor warms within 20–30 minutes, you're done. If it trips again immediately, do not keep resetting it — that's a ground fault, and it routes to an electrician.

buildNo tools schedule10 min

visibilityHow to check

With the system running and calling for heat, feel the supply and return pipes for the cold loop at the manifold — a loop full of air stays cool while its neighbours warm up.
Listen at the manifold: gurgling or trickling water sounds point to trapped air rather than a closed valve.
Confirm the zone valve for that loop is actually open before blaming air — a stuck valve looks the same from a distance (see the zone-valve cause).

buildflashlight schedule15 min

handymanHow to fix it

Bleed or purge the affected loop at the manifold: with the boiler off and the system cool enough to handle, open the loop's purge/drain and feed valves to push the trapped air out with water flow, then re-check system pressure and top up if needed.

Turn the boiler off and let the loops cool to a safe temperature before touching valves — hydronic water can be scalding.
Isolate the affected loop at the manifold (close the other loops) so incoming water is forced through the airbound one.
Open that loop's purge/drain to a bucket or hose and open the fill valve; run water through until it flows clear with no sputtering air, then close up.
Restore the other loops, check the boiler pressure gauge against the normal range on the label, top up if low, and confirm the zone warms. If pressure won't hold, that's a separate boiler-side problem for a pro.

schedule40 min savings$0–15

gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Bleeding or purging a hydronic loop and adjusting the thermostat are generally owner-permitted maintenance; boiler-side repairs remain licensed work.

verifiedWhy this one goes to a pro

A heating cable set in mortar or slab can't be diagnosed or repaired from the surface, and a ground fault in it is why the GFCI keeps tripping. Locating the break takes specialized tracing tools, and the repair must follow the cable maker's method to stay safe and warranted. Leave the circuit off and bring in a licensed electrician.

gavel Check your province first AB: licensed professionals only · BC: licensed professionals only · ON: permit + inspection required · PE: licensed professionals only · QC: licensed professionals only
Locating and repairing a buried heating cable is licensed electrician work in most provinces; confirm the provincial rule before publishing.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

verifiedWhy this one goes to a pro

Reading the boiler's pressure gauge is fine. Beyond that, restoring pressure, bleeding the boiler, or replacing a circulator means working on a closed, pressurized heating system — get it wrong and you can flood a floor, damage the boiler, or scald yourself. Have a licensed HVAC/hydronic technician diagnose and repair the boiler side.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

sort

Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.