The lounge is too hot, the bathroom is fine, and the back bedroom never gets above lukewarm. Every radiator works if you feel it, but the far ones never catch up. That is not a broken boiler. It is an unbalanced system.
Why it happens
Water takes the easiest path. The radiators nearest the boiler get the first and strongest flow, and unless something holds them back, they take more than their share. The ones at the end of the run get what is left.
It is common in homes where radiators have been added, moved or swapped over the years and nobody rebalanced the system afterwards.
What balancing is
Every radiator has two valves. One is the one you turn, often a thermostatic valve. The other, under a plastic cap, is the lockshield valve. Balancing means adjusting the lockshield on each radiator so the flow is shared properly: closing down the greedy ones near the boiler and opening up the far ones.
The target is a drop of about 11 to 12 degrees between the pipe going into each radiator and the pipe coming out.
Can you do it yourself?
You can, with two clip-on thermometers and patience. It takes a couple of hours across a whole house, starting from cold, working radiator by radiator. It is fiddly rather than difficult.
When it is not balancing
- Cold at the top of a radiator: air. Bleed it.
- Cold along the bottom: sludge. That needs a flush.
- One radiator stone cold, the rest fine: a stuck valve or a blocked radiator.
What we do
When we balance a system we check for sludge and stuck valves at the same time, because there is no point balancing around a blocked radiator. It costs nothing in parts, only time, and it is priced before we start. Tell us which rooms are cold.