Nearly every house has one room that never quite keeps up. The heating is on, the boiler is fine, the rest of the house is comfortable, and that one room stays five degrees behind and gets an electric heater in December as a permanent solution to a temporary problem.
G R Plumbing works on heating across Caterham, and a cold room is almost always one of five specific faults, each of which announces itself differently if you know where to put your hand.
Read the radiator with your hand
Turn the heating on and feel the radiator in four places: top, bottom, and each end. A radiator cold across the top and warm at the bottom has air trapped in it, and bleeding solves it in minutes. Cold across the bottom with a hot top is the opposite fault, a build-up of sludge sitting in the lower channels where flow has slowed.
Cold at one end and hot at the other, particularly on a long radiator, generally means poor circulation through that emitter, whether from partial blockage or a valve barely open. And a radiator that is uniformly cold while the rest of the house heats is either isolated at a valve or on a circuit that is not receiving flow at all.
- Cold top, warm bottom: air, so bleed it.
- Cold bottom, hot top: sludge, so the system needs cleaning.
- Cold at one end: restricted flow through that radiator.
- Uniformly cold: a closed valve or a circuit not being fed.
Valves that look open and are not
Thermostatic radiator valves fail in a specific and very common way: the pin under the head sticks down after a summer of sitting in one position, so the valve stays shut no matter what the dial says. Taking the head off and pressing the pin, which should spring back freely, identifies it in seconds and a gentle free-off or a new head fixes it.
At the other end of the radiator is the lockshield valve, which sets how much flow that radiator gets. If a previous occupant or an earlier repair closed it down, the radiator will underperform permanently while everything nearby works perfectly. That is a balancing setting rather than a fault, and it is adjustable.
- Lift the thermostatic head and check the pin springs back.
- The lockshield at the other end may simply be closed down.
- A head reading twenty on a cold room may be a stuck pin, not a setting.
Balancing: the whole-system explanation
Water follows the easiest path, which means radiators close to the boiler take the heat first and the far end of the circuit gets whatever is left. Balancing corrects that by deliberately restricting the easy circuits so flow reaches the difficult ones, and it is a methodical job of measuring the temperature drop across each radiator rather than a matter of opinion.
A house that has never been balanced usually has a recognisable pattern: warm downstairs at the front, cool at the back or upstairs at the far end. If the cold room sits at the end of the pipe run, balancing rather than any single repair is the answer.
- Rooms furthest from the boiler suffer first when a system is unbalanced.
- Balancing is set at the lockshield, measured by temperature drop.
- It costs labour rather than parts and often fixes two rooms at once.
When the radiator was simply never big enough
Some cold rooms are correctly plumbed and honestly undersized. A room with a large window, an external corner, a converted garage floor or an extension built after the heating was designed can need considerably more output than the radiator hanging in it can deliver, and nothing in the system will change that.
The correction is a properly sized emitter based on the room's heat loss rather than on what fits the wall. That is also the upgrade that lets the whole system run at a lower flow temperature, which is where modern boilers become efficient. G R Plumbing sizes those from the room rather than from the old radiator, because copying the previous size simply repeats the original mistake.
Related pages
Questions customers ask
Should I bleed a radiator that is cold at the bottom?
It will not help. Air collects at the top, so cold at the bottom is sludge settled inside the radiator. That needs flushing or a system cleanse rather than a bleed key.
My thermostatic valve is turned up but the radiator is cold. Why?
Usually a stuck pin. Take the head off and check the pin springs back when pressed. After a summer in one position it often sticks down and holds the valve closed regardless of the dial.
Is balancing worth paying for?
In a house where near radiators are scalding and far ones are cool, yes. It is labour rather than parts, it often solves more than one room, and it makes running the system at a lower, cheaper temperature possible.
Put your hand on the radiator in four places, lift the valve head, then decide between air, sludge, a stuck pin, balancing and honest undersizing. That sequence identifies almost every cold room in the country.
G R Plumbing covers Caterham for heating faults and system balancing. The contact page takes a description of which room and when.
