Adjusting lockshield valves to balance radiators
If some radiators in your home are stone cold whilst others are scorching hot, you've got an unbalanced heating system — and you're not alone. This happens because water naturally takes the path of least resistance, so radiators nearest the boiler get the lion's share of heat whilst distant rooms shiver. It's a common problem in older properties, larger homes, and systems that haven't been properly commissioned. The good news is that balancing your radiators is a straightforward DIY job that can save you money on energy bills and make your home far more comfortable. This guide walks you through the process using lockshield valves and a simple temperature measurement method. If your system has serious issues — like radiators that won't heat at all, or a faulty pump — it's worth calling a qualified heating engineer to rule out deeper problems first.
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Balancing radiators ensures equal heat distribution around the system. Start by opening all lockshield valves fully — remove the plastic cap and turn anti-clockwise until fully open.
Turn the heating on from cold. Note which radiators heat up fastest — these are the ones closest to the boiler and will need their lockshield valves partially closed.
Your target is for the temperature difference between the flow pipe (into the radiator) and return pipe (out of the radiator) to be approximately 12°C on every radiator. This is called the delta-T.
Starting with the radiator that heats up fastest, partially close the lockshield valve — typically a half to one full turn from fully open — until you achieve the correct delta-T reading.
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Frequently asked questions
Do I need special tools to balance my radiators?
You'll need a pair of adjustable wrenches or a lockshield valve key, a thermometer (a digital one works best), and ideally some pipe clips to hold the valves steady whilst you turn them. Most of these are inexpensive and available from any plumber's merchant or DIY retailer.
How long does it actually take to balance a full system?
The job itself only takes an hour or two, but the waiting is the real test — you need to allow 20–30 minutes between each adjustment for the system to stabilise and show accurate temperature readings. Plan for a full afternoon or morning for a typical three-bedroom home.
What's the difference between a lockshield valve and a TRV?
A lockshield valve is a manual isolating valve hidden under a plastic cap that controls how much water flows through a radiator; a TRV (thermostatic radiator valve) is fitted to the other end and lets you set a desired room temperature. Both work together — the lockshield balances the system, and the TRV fine-tunes comfort in individual rooms.
Can I balance radiators in a system with a combi boiler?
Yes, absolutely — the process is identical regardless of your boiler type. Combi boilers heat on demand, so you may notice more fluctuations whilst balancing, but the delta-T method still works perfectly.
What should I do if a radiator still won't heat after balancing?
If a radiator remains cold after balancing, it likely has trapped air or sludge inside — try bleeding the radiator with the bleed key first. If that doesn't work, the radiator may need flushing or replacing, so contact a qualified heating engineer.
Is balancing radiators the same as 'powerflushing' the system?
No — balancing uses lockshield valves to control water flow; powerflushing is a separate process that cleans internal scale and sludge from the pipework. You may need both if your system is old, but balancing alone will improve distribution.