If a radiator is cold at the top, bleed it to let trapped air out. If some radiators get hot quickly while others stay lukewarm, the system probably needs balancing, which means adjusting the lockshield valves so hot water reaches every radiator evenly. If a radiator is cold at the bottom, sludge is the likely cause, and bleeding or balancing won’t fix that.
Bleeding is an easy homeowner job. Balancing takes patience and is often best left to an engineer. If you’re not getting anywhere, our boiler service and repair team can help.
Bleeding a radiator
- Turn the heating off and let the radiators cool
- Put a cloth under the bleed valve at the top corner
- Open it a quarter turn with a radiator key
- Close it when water starts to come out
- Check the boiler pressure and top up if needed
- Turn the heating back on and check the radiator heats evenly
What balancing means
Water takes the easiest route round a heating system. Without balancing, radiators nearest the boiler hog the hot water and those further away stay cool. Balancing restricts the flow to the nearer radiators using their lockshield valves, so the heat spreads evenly.
How balancing works
- Bleed all radiators first
- Open all TRVs and lockshield valves fully
- Turn the heating on and note which radiators heat up first
- Close down the lockshield valve on the fastest radiator, then gradually open it a little
- Work through the radiators in order, from fastest to slowest
- Ideally, use radiator thermometers to aim for a similar temperature drop across each radiator
It’s fiddly and can take a few hours. Many homeowners prefer to have an engineer do it.
When it’s not air or balancing
| Symptom | Likely cause |
| Cold at the bottom | Sludge |
| Cold all over, others fine | Stuck TRV pin or closed valve |
| Needs bleeding every few weeks | Air getting in: leak or faulty component |
| All radiators cold | Boiler, pump or controls issue |
If the TRV is the issue, our guide to thermostatic radiator valves explains how they work.
Radiators in Bognor Regis homes
Many homes around Bognor Regis, Felpham and Middleton-on-Sea have had radiators added or replaced over the years, which often throws the system out of balance. A new boiler can also change how evenly heat reaches each room. If you’ve recently had a new boiler installed and some rooms are cooler, balancing is often the fix.
Frequently asked questions
How often should I bleed my radiators?
Only when needed, usually when a radiator is cold at the top. Many people check at the start of the heating season.
Do I need to balance radiators every year?
No. Once balanced, a system usually stays that way unless radiators are added, removed or valves are adjusted.
Can balancing save money?
A balanced system heats rooms more evenly and can let you run the boiler at a lower flow temperature, which can improve efficiency.
Still got cold spots?
If bleeding and balancing haven’t solved it, give me a ring on 07545 916929 or send me a message. I’ll come and take a look.