Quick answer
If the taps run hot but the radiators stay cold, the boiler is working and the problem is usually in the heating circuit or its controls: a thermostat with flat batteries, a programmer set wrongly, a seized pump, a stuck heating zone valve, or low system pressure locking out the heating. Check the controls, batteries and pressure gauge first — those three account for a lot of the calls we get.
Cold radiators with perfectly good hot water is a reassuring combination — it usually means the boiler itself is fine and something in the heating side is not asking it to run.
Start with the controls
- 1Turn the room thermostat well above the current room temperature and listen for a click.
- 2Replace the thermostat batteries — wireless thermostats fail quietly when the batteries go.
- 3Check the programmer is on the heating channel, and that the clock and any holiday mode are correct.
- 4Check the boiler pressure gauge; many boilers will not run heating if pressure has dropped too low.
- 5Check a smart thermostat has not lost its connection to its receiver.
If the controls are right
- Seized circulating pump — sometimes audible as a hum with no flow
- Heating zone valve stuck or its actuator failed
- Air lock in the heating circuit
- Thermostatic radiator valves seized closed after a summer of being shut
- Heavy sludge restricting circulation
Cold radiators with the heating on?
We'll find out whether it's a control, a valve, the pump or the system itself — and tell you the cost before we start.
Book a boiler repairIf the system has never been cleaned and several radiators are slow to heat, a full heating system health check as part of an annual boiler service is usually the better place to start.
When to call a professional
Safe homeowner checks stop at pressure gauges, radiator valves, controls and visible pipework. Anything involving gas, combustion, the boiler casing, the flue or internal components is work for a Gas Safe registered engineer. If you smell gas, follow the appropriate emergency gas safety guidance and do not attempt to work on the appliance.
Call 07881 963508The Betaflo recommendation
Why hot water can keep working while the radiators stay cold, and the checks worth making before you book a repair. If you'd like a second opinion before spending money, speak to us first — we'd rather tell you your boiler is fine than sell you something you don't need.
Frequently asked questions
Why would low pressure stop the heating but not hot water?
Many boilers lock out heating when pressure falls below the manufacturer's minimum while still providing hot water. Check the gauge before assuming a bigger fault.
Only one radiator is cold — same problem?
No. One cold radiator usually means trapped air, a seized valve or sludge in that panel, not a system-wide fault.
Can I free a stuck TRV myself?
Removing the head and gently pressing the pin is a recognised homeowner check. If the pin doesn't move freely, leave it to an engineer rather than forcing it.
About the author
Betaflo Heating UK
Betaflo Heating UK is founded and run by Miles Davis and Sam Boyle, Gas Safe registered heating professionals installing, servicing and repairing boilers across Tamworth, Birmingham and the surrounding areas. Our guides are written from the work we do in customers' homes every week. More about Betaflo.
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