A radiator that stays cold (or only heats up at the bottom) is one of the most common heating problems we deal with in Hull homes. The good news is that most causes are easy to fix.
Cold at the Top, Hot at the Bottom
This is almost always trapped air. When air gets into your heating system, it rises to the top of the radiator and stops hot water from filling the whole panel.
Fix: Bleed the radiator.
- Turn off the heating and wait 10 minutes for the system to cool slightly.
- Find the bleed valve at the top corner of the radiator (small square fitting).
- Use a radiator key (or a flat screwdriver on newer models) and turn it anti-clockwise a quarter turn.
- You’ll hear air hissing out. Keep the key in place.
- As soon as water starts to dribble out, close the valve. Done.
Have a cloth or small container ready to catch the water. It can be dirty.
Cold at the Bottom, Hot at the Top
This usually means sludge has built up inside the radiator. Over time, rust and debris from inside the pipes settle at the bottom and block the flow of hot water.
Fix: The radiator needs flushing or the whole system may need a power flush. This is a job for a plumber as it involves draining the system.
Completely Cold When Others Are Hot
If one radiator is stone cold while the rest of the house is warm, check these things:
- Thermostatic valve (TRV): the numbered dial on one end. Make sure it’s not set to zero or the frost setting.
- Lockshield valve: the plain cap on the other end. If someone has closed it, no water gets through. Remove the cap and turn the spindle anti-clockwise slightly.
- Stuck pin: remove the TRV head and check if the pin underneath is stuck down. Tap it gently or wiggle it with pliers. If it pops up, that’s your problem.
All Radiators Are Cold
If none of your radiators are heating up, the issue is with the heating system itself, not the radiators. Check that your thermostat is set above room temperature and that the timer/programmer is on. Check the pressure gauge on your boiler (if you have one). It should read between 1 and 1.5 bar.
Note: HJZ Plumbing does not carry out boiler or gas work as we are not Gas Safe registered. We can help with radiators, valves, pipes, and system flushing.
When to Call a Plumber
Call us if:
- Bleeding doesn’t fix the problem
- Multiple radiators have cold spots at the bottom (sludge buildup, needs a power flush)
- A valve is leaking or broken
- You need a radiator replaced or moved
Radiator repair and replacement starts from £178 + parts during working hours. Call 07450 332 474 to book.
