What causes radiators to stay cold?
Where the radiator is cold tells you a great deal about why. Use that before assuming the boiler is at fault.
Cold at the bottom, warm at the top
This is the classic sludge symptom. Iron oxide settles at the base of the radiator and blocks flow through the lower section. Bleeding will not help — the fix is cleaning the system, usually with a power flush, followed by fresh inhibitor and a magnetic filter to catch what forms next.
Cold at the top, warm at the bottom
That is air, and bleeding the radiator normally solves it. If air keeps coming back, something is drawing it in — a small leak, a pump issue or corrosion generating hydrogen inside the system. Persistent air is worth investigating rather than bleeding on a schedule.
Cold all over
Check the valves first: a thermostatic valve with a stuck pin is extremely common, particularly at the start of the heating season. Beyond that, it may be balancing — radiators nearest the pump taking more than their share — or a circulation fault.
Whole system lukewarm
If everything is warm but nothing is hot, look at the boiler, the pump and the controls rather than individual radiators. Slow warm-up across the house typically indicates circulation or heat output problems, not a radiator issue.
Need a heating engineer in Worcester?
Call the office Monday to Friday, 8:00 to 17:30, or send us the details and we will come back to you with a quote.