If the radiators near the boiler roast while the far ones barely warm, the system probably needs balancing. It costs nothing but time, and a little patience.
Gas Safe registered 25 years in the trade 12 years running the business
Written by Chris Gill, C Gill & Son Plumbing & Heating ·
What balancing does
Hot water leaves the boiler and takes the easiest path back. Radiators close to the boiler, on short pipe runs, get more than their share, and the ones at the end of the circuit get the leftovers. Balancing means partly closing the lockshield valves on the nearer radiators so water is pushed further round the system.
Done well, every radiator heats up at about the same rate and the house warms evenly. It is a different job from fixing a single cold radiator, which our guide to radiators not heating up covers.
Before you start
Bleed every radiator first, so air is not throwing off the results; our guide on how to bleed a radiator explains how. Check the boiler pressure is in the normal range. You will need a lockshield key or small adjustable spanner, a notepad and, ideally, a simple clip-on or infrared thermometer.
Step 1: find the order
Turn the heating off and let everything go cold. Open every control valve and lockshield fully. Then turn the heating on and go round the house, noting the order in which radiators start to warm. The first to warm is nearest the boiler on the pipe run, which is not always the one physically closest.
Step 2: set the lockshields
Let the system cool again, then turn the heating back on. Start with the first radiator on your list. Close its lockshield fully, then open it a quarter of a turn. Once it has warmed, measure the pipe temperature at both valves. You are aiming for the return side to be roughly 10 to 12 degrees cooler than the flow side. Open the lockshield a little more if the difference is bigger, close it a little if it is smaller.
Move to the next radiator and repeat. Radiators further from the boiler will need the lockshield opened further. The last one may need it fully open.
Step 3: check and fine-tune
Leave the heating running for an hour and go round again. If one room still lags, open its lockshield a little more and close one of the early radiators slightly. Small adjustments make a big difference. Write down the number of turns on each lockshield so you can return to them if anyone touches them.
When balancing does not work
If you have balanced carefully and a radiator or a whole floor still will not heat, the cause is probably a blocked or faulty valve, sludge in the pipework, a pump that is not up to the job or a zone valve that has stuck. Those are faults to diagnose rather than settings to adjust, and part of our central heating work.
Need it sorted? Book a central heating visit
If you would rather we balanced the system for you, or it still is not right, call or WhatsApp 07429 632804, or use the quote form.
Covering Neath, Port Talbot, Swansea and the surrounding area.
Common questions
Radiator balancing FAQs
Clear answers before you arrange a visit.
What is radiator balancing?+
Adjusting the lockshield valve on each radiator so hot water is shared evenly around the system, instead of most of it going to the radiators nearest the boiler.
Do I need a thermometer to balance radiators?+
It makes it much more accurate, but you can do a rough balance by touch and by how quickly each radiator warms.
Which valve do I adjust when balancing?+
The lockshield, under the plastic cap. Leave the thermostatic or control valve fully open while you balance.
How often do radiators need balancing?+
Usually only after work on the system, such as adding radiators or a new boiler, or if someone has changed the lockshield settings.
