When the heating comes on for winter, radiator problems show up fast. The good news is that many of them have simple causes. Here’s how to work out what’s wrong, and which jobs need a professional.
Cold at the top, warm at the bottom
This is almost always trapped air. Air collects at the top of the radiator and stops hot water filling it.
How to bleed a radiator:
- Turn the heating off and let the radiators cool.
- Hold a cloth under the bleed valve at the top corner and open it slowly with a radiator key.
- Air will hiss out. Close the valve as soon as water starts to appear.
- Check the boiler pressure. Bleeding releases pressure, and many combi and system boilers need topping back up to the level in the manufacturer’s instructions (often around 1 to 1.5 bar when cold).
If a radiator needs bleeding again and again, air is getting into the system somewhere, and that’s worth investigating.
Cold at the bottom, warm at the top
This usually points to sludge: a build-up of rust and debris that settles at the bottom of radiators and blocks the flow. Sludge also makes the boiler and pump work harder. A powerflush or chemical clean, often with a magnetic filter fitted afterwards, removes it and helps keep the system clean.
Some radiators hot, others barely warm
If radiators near the boiler get hot quickly but those furthest away stay lukewarm, the system probably needs balancing. That means adjusting the lockshield valve on each radiator so hot water is shared evenly around the house. It’s a methodical job, but it makes a big difference to comfort and running costs.
Radiator completely cold
- Check the thermostatic radiator valve (TRV) is turned up. TRV pins can stick after a summer of not being used.
- Check both the TRV and the lockshield valve at the other end are open.
- If one radiator stays cold, it may be heavily blocked with sludge, or have a fault on the valve.
Leaking radiator valves
Small drips from a valve or joint can often be fixed by tightening or re-packing the valve. Rust spots or pinhole leaks on the radiator itself usually mean it needs replacing, a common job we do alongside fitting new valves and TRVs.
When to call a professional
Call a heating engineer if the boiler pressure keeps dropping, the boiler shows a fault code, there are leaks, or several radiators have problems at once. Anything involving the gas side of the boiler must be done by a Gas Safe registered engineer.
Heating help from our team
Our plumbing team bleeds and balances systems, replaces radiators and valves, fits magnetic filters and arranges powerflushes, and our Gas Safe engineers look after boilers. For bathrooms, see our towel rail guide. See our plumbing and heating service.
We cover London and Essex, with our own engineers working every day across Chigwell, Loughton, Buckhurst Hill, Woodford, Ilford, Romford, Brentwood and Epping. Call 020 8227 0035 or request a quote.