Radiator replacement and repair in London
Radiators that never get hot, valves that will not turn, and replacements sized for the room rather than the gap.
Service overview
Radiator work splits into two: something is wrong with one you have, or you want a different one.
The diagnosis half is genuinely worth doing properly, because the same symptom has several causes and most of them are cheaper than replacement. A radiator that never gets hot is not automatically a radiator that needs changing.
The replacement half is mostly about sizing. A radiator chosen to fit a gap rather than to heat a room will underperform for as long as it is on the wall.
We work across Greater London and north Surrey, including Croydon, Bromley, Sutton, Orpington and Wimbledon. Gas Safe engineers do every gas job. See the gallery, about us or get in touch.
Get a quoteSigns you need radiators
- One radiator stays cold while the rest heat
- Cold at the bottom, hot at the top
- Cold at the top, hot at the bottom
- The thermostatic valve will not turn or has no effect
- Rust marks, weeping joints or staining on the wall behind
- The room has never been warm enough even when everything works
Reading the symptom
Cold at the top means air, and bleeding usually fixes it. Cold at the bottom means sludge settled where the flow is slowest, and bleeding does nothing for it — that radiator needs cleaning, and if several are doing it the system wants a power flush.
A radiator that is completely cold when the others are hot is different again. That is normally a stuck thermostatic valve head or a lockshield closed off, and both are quick. Older TRV heads seize in the open or closed position when they have not been moved for a season, and they can often be freed rather than replaced.
Sizing, not fitting
Radiators are rated in watts, and the output a room needs depends on its volume, its external walls, its glazing and how well it is insulated. A north-facing room with a bay window needs considerably more output than an internal room of the same floor area.
The common mistake is buying to fit the existing brackets or the space under a window. Where a room has always been cold and everything else in the system is working, the radiator is often simply too small — no amount of balancing or flushing fixes an underspecified radiator. Replacing it with a taller or double-panel unit in the same width is frequently the answer.
Balancing after any change
Adding or changing a radiator alters how water moves through the whole system. Radiators nearest the pump take the easiest route, so a new low-resistance radiator can quietly starve the far end of the circuit.
That is why balancing is part of the job rather than an extra. The lockshield valves get set so each radiator takes the flow it should, which is measured on the temperature difference across the radiator rather than guessed. Systems that were never balanced are the reason so many houses have one room that roasts and another that never warms.
How the visit goes
Diagnose before replacing
Air, sludge, a seized valve or genuine undersizing. They are four different jobs at four different costs.
Size the replacement
Output matched to the room rather than to the space on the wall.
Fit and refill
Radiator fitted, system refilled and re-dosed with inhibitor.
Balance the system
Lockshields set across the whole system so the change does not starve another room.
Standards this work is held to
BS 7593:2019
Any drain-down means the system should be re-dosed with inhibitor when refilled, and the level verified annually.
15mm and 22mm pipework
Domestic systems typically run 15mm to radiators off 22mm main runs. A system extended without upsizing the main run will struggle regardless of pump.
Underfloor heating
Underfloor circuits typically run at 35°C to 45°C flow against 65°C or more for radiators, so the two need separate control where they share one system.
Balancing by temperature drop
A correctly balanced radiator shows roughly an 11°C drop between flow and return. Measuring that difference is how balancing is set rather than guessed.
Radiators: common questions
Related to Radiators
Areas we cover
We work across Greater London and north Surrey, including Croydon, Bromley, Sutton, Orpington and Wimbledon. Pick your town.
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Burst pipes, boiler breakdowns and blocked drains across Greater London. We aim to be with you within 60 minutes.