Ignite Plumbing & Heating
Why Is My Radiator Cold at the Bottom? Norfolk Heating Guide
Sludge, airlocks, and blocked valves — a complete guide to diagnosing cold radiators in Norfolk homes.
Diagnosing your cold radiator
Before calling a plumber, it helps to narrow down the cause. Touch the top and bottom of the radiator. Feel the flow and return pipes going to it. These simple checks tell us a lot.
Cold all over — likely cause: closed valve
If the radiator is completely cold, check the TRV (thermostatic radiator valve) isn't set to zero or frost setting. Also check the lockshield valve on the other side is open (requires a spanner to adjust).
Cold at the top — likely cause: air
Air rises and creates a cold bubble at the top. Bleed the radiator using a radiator key. If it repeatedly needs bleeding, there's likely a leak elsewhere introducing air into the system.
Cold at the bottom — likely cause: sludge
As described — magnetite sludge settling in the lower sections. Power flush is the solution. Don't keep bleeding — it won't help with sludge.
Cold on one side — likely cause: partial blockage or imbalance
A vertical cold stripe suggests a blockage in one section of the radiator. Isolation, removal, and individual flushing can help, though full system power flush is usually more cost-effective.
When to call a plumber
If bleeding doesn't fix the issue, if multiple radiators are affected, or if you're losing system pressure regularly, call us for a proper diagnosis. We'll advise honestly on whether you need a power flush or something simpler.