Resources / Underfloor heating
Cold Spots with Underfloor Heating: Common Causes and Fixes
Patchy floors are usually balancing, air, coverings or layout — not a mysterious failure of underfloor heating as an idea.
Quick Answer
Most cold spots come from unbalanced manifolds, air in loops, zones not calling, thick insulating coverings, furniture blocking output, or pipe spacing that cannot meet local heat loss. Fix commissioning and finishes before redesigning the whole floor.
A warm manifold with one dead loop is a diagnosis job. A whole house that never gets there on cold days may be heat-source capacity or design output — different problem, different guide.
View printable checklist Planning aid — not a quote
What counts as a cold spot
UFH will never feel as evenly “hot to the touch” as a radiator. Comfort is a large area at modest surface temperature. A cold spot is when:
- •One part of a room is clearly cooler underfoot than the rest while the system is calling
- •A whole zone stays behind neighbouring rooms
- •Edges by doors or glazing never catch up
Slow warm-up after a deep setback is not a cold spot — that is thermal mass. See not warming up fast enough.
Common causes (ranked by how often they show up)
| Cause | What you notice | First fix |
|---|---|---|
| Unbalanced manifold | Some loops hot, others cool on the same zone | Set flow meters to design rates |
| Air in the circuit | Noisy loops, intermittent cold patches | Purge / bleed properly |
| Actuator closed / zone not calling | Whole room cool, neighbours fine | Thermostat, wiring, actuator head |
| Thick rug, carpet, underlay | Floor feels cool under soft finishes | Check design assumptions for finish |
| Furniture / cabinets on external walls | Cold strip under sofas and units | Leave a gap; accept reduced local output |
| Wide pipe centres | Cool bands between pipes on high-loss floors | Layout review; sometimes higher flow temp within limits |
| Perimeter / glazing heat loss | Cold strip by French doors and big windows | Closer pipe spacing at edges if designed in; fabric |
| Pump or heat source limit | Multiple zones fail together on cold days | Flow temperature, capacity, system pressure |
Manifold balancing — the quiet number one
Loops are different lengths. Left wide open, short loops grab the flow and long loops starve. Flow meters on a decent manifold exist so you can set each circuit toward its design rate — not so every valve can sit fully open “because that looks maximum.”
Unbalanced systems produce exactly the complaint pattern: kitchen fine, far bedroom always lagging, or one half of an open-plan zone cooler than the other.
Commissioning is not optional paperwork. “We opened all the valves” is not balancing.
Air and circulation
Air pockets stop water circulating through a loop. Symptoms include gurgles, intermittent cold patches, and flow meters that bounce or sit at zero while neighbouring circuits run.
Purge from the manifold properly. On systems converted from old radiator circuits, sludge can play a similar role — filters and flushing matter more than people expect.
Coverings and furniture
Design output assumes a stated floor finish. Tile conducts well; thick carpet and underlay do not. Change the finish after install and the room can fall short even when the pipe is circulating correctly.
Large rugs and sofas tight to external walls create local cold spots by design — you have covered the emitter. Leave a gap where you can, and do not judge the whole system from the strip under a sofa.
Pipe spacing and layout
Wider centres put less pipe under each square metre. On a low-loss room that can be fine. On a high-loss room (big glazing, exposed wall) you feel cool bands or a floor that never quite satisfies the thermostat.
Perimeter loops with tighter spacing near external walls and doors are a design choice, not a luxury. If the layout was drawn for mild assumptions, cold-weather performance exposes it.
Diagnostic flowcharts
Use these to decide which problem you have before you start turning valves at random.
1. One zone cold vs whole house
Go to flowchart 2 (loop & controls). Unlikely to be whole heat-source capacity.
Check heat source, primary flow temp, pump and system pressure first — then individual loops.
2. Single-zone cold spot
Fix setpoint, schedule, holiday mode, batteries or pairing. Stop here until it calls.
Continue ↓
Actuator, wiring, pump, isolation valves, air lock. Purge and re-test.
Continue ↓
Balance manifold to design rates. Re-check underfoot after the floor has time to respond.
Continue ↓
Rugs, thick underlay, cabinets tight to external walls. Adjust before redesigning pipework.
Review layout spacing, local heat loss (glazing), and design flow temperature.
3. Slow to warm vs truly cold
Likely thermal mass + setbacks. See not warming fast enough. Steady controls help more than higher flow temps.
True cold spot or capacity issue. Use flowchart 1 → 2, then heat source if all zones fail.
The detailed tick-list below is the same logic in checklist form — use whichever suits how you work on site.
Troubleshooting checklist
Work top to bottom. Do not jump to “wrong pipe spacing” until the simple items are cleared.
- ☐Zone setpoint is above current room temperature
- ☐Schedule / holiday mode is not holding the zone off
- ☐Wireless thermostat still paired and powered (batteries)
- ☐Other zones not stealing all the heat priority if the system sequences
- ☐Actuator on the problem loop is open (warm head / visual indicator)
- ☐Circulating pump is running when heat is demanded
- ☐System pressure is in the normal range for the install
- ☐Flow meter on the problem loop is not sitting at zero
- ☐Flow meters are not wildly unbalanced vs neighbouring loops
- ☐Flow and return temperatures look sensible for the design
- ☐Loops purged — no persistent gurgle or bouncing flow meters
- ☐Manifold balanced toward design flow rates (not all valves fully open)
- ☐Filter / strainer checked if the system was converted from old radiators
- ☐Thick rugs or underlay not covering most of the heated area
- ☐Large furniture not tight against external walls over the pipe
- ☐Finish matches what the output calculation assumed (tile vs carpet)
- ☐Compare layout drawing — pipe centres in the cold area
- ☐Check room heat loss vs design output (glazing, extensions, fabric)
- ☐If every zone fails on cold days — heat source capacity / primary flow temp
Most domestic cold-spot call-outs are solved in the controls and manifold blocks. Layout and heat-loss reviews are the minority — but they matter when the water side is healthy and the floor still fails.
When every room is cold
If no zone performs on a cold day, you are not looking at a single loop. Think heat source capacity, primary flow temperature, undersized plant, or a building that loses more heat than the design assumed.
Heat pump angle: not heating the house properly. Response time vs cold spots: not warming up fast enough.
Devon & Cornwall notes
- •Large glazed openings and patio doors are common — perimeter loss shows as cold strips
- •Solid-wall rooms need honest heat-loss figures or the floor is asked to do the impossible
- •Overlay renovations still need proper commissioning — new boards do not balance themselves
- •Mixed ground-floor overlay + upstairs joist systems means two layout logic sets, one heat source
Honest bottom line
Cold spots are usually water not going where the design said it should — or heat not getting through the finish into the room. Balancing, air and coverings fix more floors than product swaps.
If the manifold is healthy and one room still fails on design days, look at spacing, local heat loss and flow temperature. If the whole house fails, look at the heat source and the fabric — not only the pipe in the floor.
Frequently asked questions
Should every loop show the same flow rate?
No. Longer loops and higher-loss rooms often need more flow. Balance to design, not to identical numbers for the sake of neatness.
Can a rug cause a real cold spot?
Yes. Thick rugs and underlay reduce output into the room. Small rugs are usually fine; wall-to-wall insulating finishes need to match the design.
Is a cold strip by the patio doors normal?
Some edge effect is common where heat loss is highest. Persistent cold bands may mean spacing or output was not designed for that wall.
Will turning the flow temperature up fix it?
It can mask mild shortfalls. It will not clear air, open a closed actuator, or balance starved loops — and it costs efficiency on a heat pump.
Next step
Get a realistic planning band for your home, then use the checklist when you speak to installers.