Heating Problems
Heating Not Working? A Full Troubleshooting Guide
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
No heat at all, or heat that won’t reach the radiators — this guide walks through the usual causes in order, the safe checks you can do yourself, and when to call a Gas Safe engineer.
Quick answer: Start with the basics — is the boiler firing, is there power to the programmer, and is the thermostat calling for heat? If the boiler works but radiators stay cold, it’s usually a thermostat, a pump, or air/sludge in the system. No response at all points to power or pressure.
Common Causes
Why the heating isn’t working
Work through these in order. The colour on the left shows whether it’s usually a safe homeowner check or a job for an engineer.
| What you see | Likely cause | What to do |
|---|---|---|
| No heat and no boiler response | Power, pressure or programmer | Check the spur, pressure gauge and programmer settings |
| Boiler fires but radiators stay cold | Thermostat not calling, or pump fault | Check the thermostat and its batteries; if fine, book an engineer |
| Only some radiators cold | Trapped air or sludge | Bleed the radiators and balance the system |
| Heating comes on then quickly off | Thermostat or short-cycling | Check the thermostat position and schedule |
| Hot water works but no heating | Diverter or motorised valve | Needs an engineer to check |
| No heat in a cold snap | Frozen condensate pipe | Thaw the external pipe, then reset |
Safe Checks
What you can safely check yourself
Safe to check
- The programmer is set to come on and is in ‘heating’ mode
- The thermostat is above room temperature, with fresh batteries
- The pressure gauge reads around 1.3 bar (top up if low)
- Bleed any radiators that are cold at the top
Stop and call us if…
- You can smell gas — leave the property and call 0800 111 999
- There’s no heat in extreme cold and someone at home is vulnerable
- The boiler is leaking water
Engineer Insight
What we usually find
Most ‘no heating’ calls fall into two camps: the boiler isn’t firing (power, pressure, programmer), or it fires but the heat isn’t circulating (thermostat, pump, air or sludge). We work through it in that order — the free checks first — so you only pay for what actually needs fixing.
Costs
What repairs typically cost
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Heating not working — your questions answered
Why is my heating not working but I have hot water?
That usually points to the diverter or a motorised valve — the boiler heats water fine but isn’t sending it to the radiators. It’s a common, fixable fault an engineer can confirm.
Why won’t my radiators heat up even though the boiler is on?
Either the thermostat isn’t calling for heat, the pump isn’t circulating, or there’s air or sludge in the system. Bleeding radiators and checking the thermostat covers the easy causes.
What’s the first thing to check if the heating stops?
Check the programmer is set to come on, the thermostat is above room temperature with fresh batteries, and the pressure gauge reads around 1.3 bar.
Could low pressure stop my heating?
Yes. If pressure drops too low the boiler locks out and won’t heat. Top up to about 1.3 bar with the filling loop and see if it restarts.
When should I call an engineer for no heating?
If the boiler won’t fire after the basic checks, if hot water works but heating doesn’t, or if there’s any gas smell or leak, call a Gas Safe engineer.
Related
Keep troubleshooting
Boiler runs but radiators stay cold — pump, valve and sludge causes.
Read guideHeatingThermostat Not WorkingBlank or unresponsive stats — batteries, settings and wiring.
Read guideHeatingRadiators Cold But Boiler WorkingTrapped air, sludge and balancing — and how to tell them apart.
Read guideBoiler ProblemsBoiler Not Turning OnIf there’s no boiler response at all.
Read guidePressureHow to Repressurise a BoilerClear a low-pressure lockout by topping up to 1.3 bar.
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.
No heat and stuck? We’ll get it running.
Book a Gas Safe engineer to diagnose the heating, or call and describe what’s happening — we’ll give you an honest steer before anyone comes out.
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