All about balancing radiators by The Purple Plumbing People

At this time of year, The Purple Plumbing People get inundated with calls regarding the poor performance of central heating systems. It is very often a fairly simple remedy, which doesn’t require the expense of a ‘call-out’ fee. Roly Paterson of The Purple Plumbing People is happy to share this guide that his company produces about balancing radiators.

Balancing Radiators

An unbalanced radiator system may show up as having some radiators becoming quite hot while others stay warm or even cold.


The reason for this is quite simple. Water will find the least path of resistance and use it to the detriment of all other routes.

Therefore, if a system pump is capable of circulating 100 units per minute and you have 10 radiators, you need each radiator to use 10 units per minute of hot water. In an unbalanced system, one radiator may be using 30 units per minute and another 20 units a minute. Straight away that’s half the circulated water into only two radiators. Other radiators on the system will have to share the remaining water and it’s easy to see how some may not get any at all.

The solution:

It can be very time consuming to perfectly balance a system and, whilst a good heating engineer may have a quick go at it, it’s the homeowner that really needs to spend the time getting it right.

A standard modern radiator should have two valves, one at each end. The big, chunky valve is the “TRV” which is the Thermostatic Radiator Valve, with the other end being a ‘lockshield’ valve. It’s the lockshield end that we use to balance the system.

All the TRV’s should be working and all then need to be set on number 3.

With the system running – give it 10 minutes or so to come up to temperature.

Go around the house and check on ALL the radiators. You are looking for the one or two that are hotter than all the rest. These are taking more than their share of the available water flow and need to be shut down a bit. This includes the towel rails, so please check these as well.

ON THE LOCKSHIELD END ONLY: Remove the white cap which may have a tiny screw holding it in place or may be a simple push fit cap. Beneath the cap there is a shaft which will be either a square section or at least have two ‘flats’ on it, giving you the opportunity to turn it with either a small spanner or a pair of grips. Remember ‘Righty tighty – Lefty loosey’. You need to shut this radiator down (righty tighty) in ‘half a turn’ increments until the radiator temperature drops slightly. This can take hours to determine, as you’ll need to wait each time for the temperature of that radiator to settle.

When that radiator temperature has dropped a little. Turn it back up just a bit, in quarter turn increments (lefty loosey) to get the temperature back to where it was before you started shutting it down.

Once you have achieved this, move on to the next radiator and so on.

Once you have got all the radiators hot, it may need a slight further tweak but, essentially, you have now balanced the system. Put the little caps back on and don’t let anyone alter the lockshield and undo all your hard work.

New radiators, full drain downs, extensions and attic conversions are all possible causes of the system becoming unbalanced.

If you need any plumbing advice or work done, please contact Roly Paterson at The Purple Plumbing People: 01367 252807 or email