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The Complete Guide to Central Heating Systems
Most guides to heating in London start and end with the boiler. This one doesn't, because most of what determines how comfortable your home actually feels — which rooms warm up, how evenly, how quickly, how efficiently — happens in the system around the boiler, not inside it.
Quick answer
A central heating system is the boiler plus everything it serves: pipework, radiators, controls and balance. Most heating problems — cold rooms, uneven heat, high running costs — sit in that "everything else", not in the boiler itself.
This guide walks through the whole system as a homeowner needs to understand it: what each part does, the most common ways it goes wrong, and where to start if something isn't right.
The parts of a heating system, beyond the boiler
A wet central heating system is the boiler, a pump that circulates hot water, pipework that carries it around the property, radiators (or underfloor loops) that release the heat into each room, and controls that decide when and where it runs.
Every one of those parts can be the reason a room stays cold, even when the boiler itself is working exactly as it should. Diagnosing which part is the actual cause is most of the job.
- Radiators — sized and positioned to match each room, with a TRV for local control
- Pipework — carries hot water to every radiator, prone to sludge build-up over years
- Pump — circulates water around the system at the right flow rate for its size
- Controls — thermostats, zone valves and TRVs that decide when and where heat goes
Why one cold room is rarely a boiler problem
A single room that never warms up properly, while the rest of the house is fine, almost always points to something local to that room or its position in the system: an undersized radiator, a stuck TRV, or a system that was never rebalanced after an extension added load.
A boiler heats the water; getting that heat to the right place, in the right amount, is the system's job. That's the distinction this whole site is built around.
When to consider a whole-system approach
If more than one room runs cold, if the system has been extended or altered over the years without a full reassessment, or if it has never been power flushed, a whole-system survey usually finds more than a single-radiator fix would.
This is planned work worth scoping properly rather than chasing one symptom at a time — see our system upgrade and rebalancing service for what that survey actually covers.
How to read your own system before calling anyone
Before arranging a professional survey, taking some systematic notes about your heating system's behaviour can help identify whether your issue requires whole-system attention. Start by mapping which specific rooms feel colder than others, noting whether this occurs consistently, only in the mornings, or when multiple rooms are in use. Pay particular attention to radiator temperature patterns: a radiator cold at the top typically indicates trapped air, while cold at the bottom often suggests sludge accumulation, pointing toward different potential solutions. Documenting these observations creates a clear timeline of symptoms rather than general impressions.
Next, gather what you know about your system's history. When was the last power flush performed, and has the system been rebalanced since any modifications? If your home has been extended, or if radiators have been added or removed since the system was originally designed, the hydraulic balance is likely compromised. Even without exact dates, noting whether these services have ever been completed provides crucial context. This historical perspective helps determine whether symptoms stem from age-related wear, inadequate maintenance, or a system that has simply outgrown its original design.
- Record which rooms are cold and whether the issue is constant or intermittent.
- Check each radiator: note if cold spots are at the top (air) or bottom (sludge).
- Estimate system age and note any past power flushing or rebalancing work.
- Identify any home extensions or radiator changes since the system was installed.
Fixed quote before we start
Every job is priced after a proper survey — not an open-ended day rate that climbs while someone guesses.
Whole system, not one part
Radiators, pipework, controls and balance are assessed together, so the fix addresses the actual cause, not just the symptom.
Any boiler brand
This work is independent of who made your boiler — we work with the system, not a specific manufacturer.
Our services
Related heating services
London coverage
Available across all 33 boroughs
Same approach from Barking to Richmond. Browse a borough for local housing notes, or send your postcode for a fixed-price slot.
Frequently asked questions
Is my heating problem about the boiler or the system?
If the whole house struggles to heat, or the boiler itself is faulting, that's more likely boiler-specific — outside what we cover. If it's one or two rooms, uneven heat, or a system that feels tired despite the boiler working fine, that's a system issue, which is exactly what we address.
Do you work on any make of boiler?
We don't repair boilers at all — we work on the system around it: radiators, pipework, power flushing, underfloor heating and controls. That work is independent of boiler brand.
How do I know if my system needs a power flush or a rebalance?
Cold spots within individual radiators (bottom cold, top warm) usually point to sludge and suit a power flush. Some radiators hot and others cold across the whole house usually points to a balance problem. Often both are present together — see our power flush guide and radiator balancing guide.
What should I check before booking a survey?
Which rooms run cold, roughly how old the system is, and whether it has been power flushed or rebalanced before. That's usually enough for us to scope the right first step.
Planning heating work in your London home?
Tell us the room and the system. Fixed quote, agreed survey slot, confirmed before you book.
Get a fixed quote