There's nothing worse than turning on your heating only to find one or more radiators staying cold. Before you panic, there are several common causes – and many you can fix yourself. Let's work through them.
Step 1: Identify the Problem
First, check how your radiator is behaving:
Completely cold?
Could be a closed valve, airlock, or no water flow
Cold at the top, warm at the bottom?
Trapped air – needs bleeding
Warm at the top, cold at the bottom?
Sludge build-up – needs flushing
Cold patches in the middle?
Internal corrosion or sludge
Fix 1: Bleed Your Radiator
If your radiator is cold at the top but warm at the bottom, air is trapped inside. This is the most common issue and the easiest to fix.
How to bleed a radiator:
- 1 Turn your heating on so the system is under pressure
- 2 Find the bleed valve (small square nut at the top corner of the radiator)
- 3 Hold a cloth underneath and use a radiator key to turn anti-clockwise
- 4 You'll hear hissing as air escapes – once water starts dribbling out, close the valve
- 5 Check your boiler pressure – you may need to top it up afterwards
Fix 2: Check the Valves
If your radiator is completely cold, the valves might be closed or stuck.
- Thermostatic valve (TRV): Usually on the left with numbered settings. Make sure it's not set to 0 or the frost setting (*). Turn it up to 3-5.
- Lockshield valve: On the opposite side, covered by a plastic cap. This controls flow balance – usually shouldn't be touched, but if someone's been fiddling, it might be closed.
- Stuck valve pin: Sometimes the pin inside a TRV gets stuck. Remove the TRV head and gently tap the pin with a hammer or use pliers to free it.
Fix 3: Call a Plumber (Sludge Issues)
If your radiator is warm at the top but cold at the bottom, there's likely sludge (rust and debris) sitting in the bottom of the radiator. This blocks water flow and reduces efficiency.
This needs professional attention. We can remove and flush individual radiators, or recommend a full system powerflush if multiple radiators are affected. Ignoring sludge can damage your boiler over time.
Other Things to Check
- Boiler pressure: Check the gauge on your boiler. It should be between 1 and 1.5 bar when cold. Too low? Use the filling loop to top up.
- Is it just one radiator? If all your radiators are cold, the problem is likely with the boiler or pump, not the radiators.
- Radiator distance from boiler: Radiators furthest from the boiler may need balancing – adjusting the lockshield valves so water flows evenly throughout the system.
Still Cold? We Can Help
Everyday Plumbing can diagnose and fix radiator problems, replace faulty valves, flush sludge from your system, and even fit new radiators if needed. We cover Kettering, Corby, Wellingborough, Rushden and all of Northamptonshire.