Radiator not getting hot at all
A radiator that refuses to heat up can be frustrating, especially when the rest of your heating system seems fine. This problem is surprisingly common, particularly in homes with older systems or after the heating hasn't been used for a while. The good news is that nine times out of ten, it's caused by something straightforward — a closed valve, a trapped air pocket, or a thermostatic valve stuck in the off position. This guide walks through the most common culprits and the practical steps you can take to get that radiator working again. Most of these checks are well within the capability of any homeowner with a basic toolkit, though if you've worked through everything and the radiator is still stone cold, it's time to call a Gas Safe registered engineer to rule out issues with your pump or zone valves.
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Most likely cause & what to check
Check both valves on the radiator are open — the lockshield valve and the TRV or manual valve.
For TRVs: check the number setting isn't at 0 or frost symbol. Turn to 3 or 4.
TRVs can seize in summer — remove the TRV head and free the pin beneath with a screwdriver.
Try bleeding the radiator in case there is an airlock.
If still cold despite both valves open, the issue may be with the pump or a closed zone valve.
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Frequently asked questions
Why is one radiator cold when all the others are hot?
When just one radiator stays cold whilst others work fine, it's almost always a valve issue on that radiator, an airlock, or occasionally a stuck thermostatic valve. The good news is the rest of your system is functioning properly, so the fix is usually straightforward and localised to that single radiator.
Can I bleed a radiator myself, or do I need an engineer?
Bleeding a radiator is a straightforward DIY task — you'll just need a radiator key and a cloth to catch any water. Simply locate the bleed valve (usually at the top corner of the radiator), open it slightly with the key, and let air escape until water flows out, then close it again. Make sure your boiler is on but the heating isn't actively running when you do this.
What's the difference between a lockshield valve and a TRV?
The lockshield valve is a simple on-off valve with a protective cap — it should be fully open to allow water flow. The TRV (thermostatic radiator valve) has a numbered dial and controls temperature automatically by restricting flow when the room reaches the set temperature; if yours is on 0 or the frost symbol, it's shut off completely.
My TRV feels stuck — is it broken?
TRVs can seize up during summer months when they're not in use regularly, but they're often salvageable. Remove the valve head and gently free the pin underneath with a flat-head screwdriver; if it won't budge, a gentle tap with a hammer on the screwdriver can help loosen it without damaging the valve itself.
Should a lockshield valve be fully open or partially closed?
The lockshield valve should be fully open — it's there to allow you to balance your heating system, not to restrict flow to a single radiator. Once it's fully open, it should stay in that position unless a heating engineer has specifically adjusted it during system balancing.
How do I know if my heating pump has failed?
If all your radiators are cold despite valves being open and you've ruled out airlocks, listen near your boiler for a humming sound from the pump — no hum suggests pump failure. You may also notice the boiler trying to fire but no heat reaching the radiators; this requires a Gas Safe engineer to diagnose and repair.