A slightly cooler return end can be normal. A distinct band of lower bars that stays cold while the top is hot after warm-up can point to restricted circulation, sometimes from debris or sludge. The heat pattern alone cannot show where a restriction is or what treatment the system needs.
Compare like with like
Check the rail during a normal heating cycle and note whether the whole lower section stays cold. Compare nearby radiators on the same cycle. If several units have a similar pattern or the issue began after central heating work, share that information with the engineer. If only this rail is slow and others heat normally, its valves and local circulation are worth investigating.
What an engineer can check
Ask the engineer to establish whether the problem is local to the rail or part of the wider circuit. That helps decide whether a valve, balancing, or cleaning needs attention. Replacing the rail alone may leave a system-wide problem in place. See our repair or replace guide if the rail also shows corrosion or leakage.
Frequently asked questions
Will bleeding fix cold lower bars?
Bleeding releases air that collects high in the rail. Persistent cold lower bars with a hot top call for a circulation check.
Does a cold bottom always mean the system needs flushing?
An engineer should assess circulation and system condition first. The choice of treatment depends on the cause and the condition of the equipment.
For other symptoms, see the complete towel radiator troubleshooting guide.