Why a heating system is balanced and an ordered way to set the lockshield valves for even heat.
Balancing shares the water out so each radiator gets the flow its heat output needs. On an ordinary two-pipe circuit it is usually done at the lockshield valves. The easiest paths may need closing down so the harder branches get their flow, and the nearest radiator is not always the easiest path.
- Confirm that the system is clean, properly filled and vented before final balancing.
- Identify the fitted valves and the specified method. Conventional lockshields, preset TRVs and pressure-independent valves are commissioned differently.
- For manual lockshield balancing, set the valves, pump and heat demand to the starting positions the procedure gives.
- Let the system stabilise before taking flow and return temperatures or measuring flow.
- Adjust each branch to its design duty. Check temperature drops against the design and the current load: equal flows, or equal drops, are not the target for every system.
- Recheck affected branches and normal control operation after adjustments, then record the settings and measurements.
The aim is enough heat in every room at the intended water temperatures and controls. Radiators serving rooms with different heat losses may need different flow rates. Follow the system designer’s duties and the valve manufacturer’s commissioning procedure.
Why balancing saves energy
An unbalanced system wastes energy in a way that is easy to miss. The radiators on the easiest paths take more flow than they need while the far rooms stay cool, so the usual response is to turn the boiler's flow temperature up or run the heating for longer, which overheats the near rooms. Once each radiator receives the flow it was sized for, every room reaches temperature at the intended flow temperature. The water also comes back cooler, and a condensing boiler only condenses, and so works at its best efficiency, when its return water is cool enough. Balancing does not need the pump at full speed either: with the flow shared properly, the pump is set to the duty the system actually needs.
One radiator stone cold, the rest fine
When one radiator is cold but the others heat, start at that emitter and its branch. Check for a closed wheelhead or lockshield, a thermostatic valve stuck shut, then trapped air or a blockage. Those local causes fit the pattern better than a boiler or pump fault affecting the whole circuit; check the radiator's valves before rebalancing everything.
Auto-balancing TRVs
Some thermostatic radiator valves balance themselves. A cartridge inside holds the flow at the rate set for that radiator, whatever the other valves are doing. On Drayton's auto-balancing valves the insert is set from the radiator's output, and the lockshield is left fully open and used only to isolate the radiator. The valves are supplied in their commissioning position. Leave them there while the system is filled, drained, refilled or cleaned, and set each insert to its radiator's output only after that. Fit the valve the right way round for the flow direction marked on it. Keep the blowtorch away too: the instructions warn against making capillary joints near these valves, because the heat can damage their internal parts.