Written by Micky Down, Micky's Property Services ·
Start with the simple checks
Before assuming the worst, check the obvious. Is the radiator valve actually open? Thermostatic valves get knocked to zero, and lockshield valves at the other end can be closed after decorating. Is the heating on and are other radiators warm? If every radiator is cold, the problem is with the system rather than the radiator.
If just one radiator is cold or partly cold, feel where the coldness sits, because the pattern tells you a lot.
Radiator cold at the top: trapped air
A radiator that is warm at the bottom but cold at the top almost always has air trapped inside. Air rises, so it collects at the top of the radiator and stops hot water filling the whole panel. The fix is bleeding the radiator, which releases the air through the small bleed valve at the top corner.
Bleeding is a safe DIY job: you need a radiator key, a cloth and a container. If the same radiator needs bleeding again and again, though, air is getting into the system somehow and that is worth investigating.
Radiator cold at the bottom: sludge
A radiator that is warm at the top but cold along the bottom usually has a build-up of sludge, a black sediment that settles in the bottom of the panel and blocks the flow. Sludge builds up over years as the system corrodes gently from the inside.
A single sludged radiator can sometimes be taken off and flushed through, but sludge in one radiator usually means sludge in the system, and a proper clean may be the better answer. This is not a DIY job.
Radiator completely cold: valve or balance
A radiator that stays stone cold while others heat up often has a stuck thermostatic valve. The pin inside the valve body seizes, especially after summer when the valve has sat untouched for months, and no amount of turning the head will open it. Freeing or replacing the valve sorts it, and our radiator valves page covers that work.
Sometimes the system simply needs balancing: the radiators nearest the boiler take most of the hot water and the furthest ones get the dregs. Balancing adjusts the lockshield valves so every radiator gets its share.
When to call someone
Bleeding a radiator is a reasonable DIY job. Beyond that, stuck valves, sludge, balancing and anything involving draining the system down are best left to someone who does it regularly, because a small mistake can mean a leak or a system that will not refill properly.
If a valve is weeping as well as stuck, our leaking radiator repair page covers that. Any gas work is carried out by Gas Safe registered engineers.
Need it sorted? Book a heating repair
If bleeding has not solved it, or you would rather not tackle it yourself, we can diagnose and fix cold radiators, replace stuck valves and balance the system. Get in touch or call 07735 852901 to book a visit.