Heating Problems
Heating On But House Still Cold? Why and What To Do
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
If the heating’s running and radiators are warm but the house never feels warm enough, the issue is usually heat loss, undersized or sludged radiators, or a system that needs balancing — rather than a boiler fault.
Quick answer: If radiators get hot but rooms stay cold, the heat is being produced but lost or unevenly distributed. Common causes are poor insulation and draughts, radiators that are undersized or sludged, or an unbalanced system where some rooms take all the heat.
Common Causes
Why the house won’t warm up
These are the usual causes. The colour on the left shows whether it’s something you can improve yourself or a job for an engineer.
| What you notice | Likely cause | What to do |
|---|---|---|
| Rooms slow to warm up | Heat loss — draughts and poor insulation | Draught-proof and insulate where you can |
| Radiators warm but small for the room | Undersized radiators | An engineer can advise on upgrading |
| Some rooms colder than others | Unbalanced system | Balance the radiator valves |
| Warm at the top, cold at the bottom | Sludge reducing output | A powerflush restores output; book an engineer |
| House cold despite hot radiators | Draughts and heat loss | Seal gaps; add insulation where practical |
| Heating can’t keep up in winter | Boiler undersized or system tired | An engineer can assess the system |
Safe Checks
What you can improve yourself
Worth trying
- Draught-proof doors, windows and letterboxes to cut heat loss
- Insulate the loft and any accessible pipework
- Bleed radiators and balance the valves so heat reaches every room
- Close curtains at dusk and keep radiators unobstructed by furniture
Where an engineer helps
If radiators are clearly undersized, the system is sludged, or the boiler can’t keep up in the cold, an engineer can advise on balancing, a powerflush, larger radiators, or whether the boiler is right for the property.
Engineer Insight
What we usually find
When the radiators are hot but the house is cold, the boiler is usually doing its job — the heat is being lost or badly distributed. Draughts and thin insulation are the biggest culprits in older North London homes. Balancing the system and clearing sludge helps a lot; occasionally a room simply needs a bigger radiator to match its heat loss.
Costs
What improvements typically cost
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
House still cold — your questions answered
Why is my house cold when the radiators are hot?
The heat is being produced but lost or unevenly spread. Draughts, poor insulation, undersized radiators and an unbalanced system are the usual reasons — not a boiler fault.
What is balancing a heating system?
Balancing adjusts each radiator’s valve so hot water is shared evenly, rather than the nearest radiators taking most of the heat. It’s a common fix for rooms that never warm up.
Could sludge be making my rooms cold?
Yes. Sludge reduces a radiator’s heat output, especially near the bottom. If radiators are warm at the top but cool below, a powerflush usually restores full output.
Do I need bigger radiators?
Sometimes. If a room loses more heat than its radiator can produce — common in extensions or rooms with lots of glazing — a larger radiator matched to the room helps. An engineer can size it correctly.
What’s the cheapest way to make my home warmer?
Draught-proofing and insulation give the best return, followed by balancing the system and clearing sludge. Our insulation and energy-saving guides cover the low-cost steps.
Related
Keep improving
Air, sludge and balancing — the mechanics behind cold rooms.
Read guideEnergyInsulation Tips for Lower BillsLow-cost ways to cut heat loss and warm your home faster.
Read guideEnergyHow to Reduce Heating BillsPractical steps that keep you warmer for less.
Read guideCentral HeatingPowerflush GuideRestoring radiator output when sludge is the problem.
Read guideEnergyHow to Set Your Heating ScheduleGet the timing right so the house is warm when you need it.
Read guideHeatingHeating Problems HubAll our heating and radiator guides in one place.
Browse guidesBrowse all Heating Problems guides, or head back to the Help & Advice Centre.
House won’t warm up? Let’s improve it.
Book an engineer to balance the system, clear sludge or advise on radiators, or call for a steer on the cheapest wins first.
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