Radiators are cold but boiler is firing
There's nothing more frustrating than hearing your boiler rumble to life whilst your rooms remain stubbornly cold. This common problem typically strikes during winter when you need your heating most, and it affects countless UK homeowners every season. The good news is that in most cases, the fault lies somewhere manageable—trapped air in the system, incorrect pressure, or a valve issue—rather than a catastrophic boiler failure. This guide walks you through the logical troubleshooting steps a qualified engineer would take, starting with the simplest checks before moving to more technical territory. Most issues can be resolved with basic tools and a bit of patience, though if you're uncomfortable working with your heating system or suspect a pump failure, it's absolutely the right call to ring a Gas Safe registered engineer rather than risk making things worse.
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Most likely cause & what to check
Check your room thermostat — ensure it's set above the current room temperature.
Check the boiler pressure — it should be 1–1.5 bar.
Bleed your radiators to release any trapped air.
After bleeding, recheck and repressurise if needed.
Check whether all radiators are affected or just some — faulty TRV valves may be the cause.
If all radiators are cold despite correct pressure, the circulating pump may have seized.
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Frequently asked questions
Why would my boiler fire up but the radiators stay cold?
The boiler firing doesn't guarantee heated water is reaching your radiators—it could be trapped air blocking circulation, incorrect system pressure, a faulty pump, or closed TRV valves preventing flow. Think of it like a blocked pipe: the boiler is working, but the water highway is congested or closed.
Is it safe to bleed radiators myself?
Yes, bleeding radiators is one of the safest DIY heating jobs you can tackle. You'll need only a radiator bleed key (a few quid from any plumber's merchant), and the worst that happens is a bit of water spillage—just pop a cloth underneath to catch drips.
How do I know if my boiler pressure is too low?
Your boiler has a pressure gauge on the front (usually digital or an analogue dial) that shows the current pressure in bar. At 1–1.5 bar, you're in the safe zone; anything below 1 bar typically triggers a lockout or poor heating performance.
What's a TRV valve and why would it cause cold radiators?
A Thermostatic Radiator Valve (TRV) sits on the side of each radiator and automatically reduces flow when the room reaches the set temperature. If it's stuck closed or set incorrectly, that radiator won't heat up—check the dial is turned to at least the middle position.
If all radiators are cold and pressure is fine, is my pump broken?
A seized pump is a strong possibility if pressure and thermostats check out but nothing heats. You might also notice the boiler cycling on and off repeatedly, which is the system's way of flagging that water isn't circulating—this calls for a registered engineer to diagnose and replace the pump.