When a Woolwich radiator runs cold or the heating won’t hold pressure, the problem often lies in the system water, not the boiler. Hard water and sludge are the quiet enemies of heating systems across SE18 — and in some Royal Arsenal blocks there’s no boiler at all, because the heat arrives from a shared network.

In Woolwich, many heating faults start with the system water

Cold spots at the bottom of radiators, a boiler that keeps cutting out, a system slow to warm — these point less often to a broken part than to what’s circulating inside the pipes. Woolwich is in a hard-water area; Thames Water describes its whole regional supply as hard (source). Two separate problems build inside a sealed heating system: limescale, which hard water drives onto hot surfaces such as the heat exchanger; and corrosion, which — where the water isn’t properly protected by inhibitor — produces black iron-oxide sludge, or magnetite. They’re distinct mechanisms with distinct fixes, though both are made worse by neglect.

That sludge is heavy. It settles in radiator bottoms, blocks narrow bores, clogs the pump and jams valves — the classic ‘cold at the bottom, hot at the top’ radiator, or a whole downstairs that won’t heat. Left alone it drives up bills and can wreck a pump or heat exchanger. Before recommending a flush, a good engineer checks the simpler causes first: trapped air needing a bleed, a stuck TRV, poor balancing, or a pressure problem. Where sludge is the cause, the fix is rarely a single new part; it’s cleaning the water and protecting it, which is where the recognised standard comes in.

The British Standard for this work is BS 7593:2019, published by BSI (source) — the code of practice for preparing, commissioning and maintaining domestic central heating and cooling water systems. It sets out that a system should be chemically cleaned and flushed, dosed with inhibitor, fitted with a permanent in-line filter, water-tested annually, and re-dosed in line with the standard. It’s worth knowing this is a domestic standard — BSI is explicit that it doesn’t apply to commercial or municipal premises — but for a Woolwich house or flat with its own system, it’s the benchmark a good engineer works to.

Where the wet work ends and the gas work begins

Central heating repair sits across a legal line that’s easy to miss. A competent plumber can install and repair the ‘wet’ side of a system — the HSE confirms that a non-registered person may carry out wet work (source), meaning water pipes and radiators. But any work on the gas boiler itself, and the final connection of the water pipework to the boiler, must be done by a Gas Safe registered engineer.

In practice that means replacing a radiator, freeing a stuck valve, sorting a leaking joint or fitting a filter can be wet work — but if the fault is inside the boiler, or the boiler needs disconnecting and reconnecting, that’s Gas Safe territory. Many Woolwich heating firms hold both competencies; the point is to check, not assume. You can verify Gas Safe status and the exact work categories on the Gas Safe Register (source) before work starts. If the boiler is the thing that’s actually failed, our page on boiler repair in Woolwich is the better starting point.

Communal heat networks: when there’s no boiler to repair

Woolwich has a wrinkle that a standard heating page ignores. In parts of Royal Arsenal Riverside, homes have no individual boiler — SSE Energy Solutions describes (source) a district energy centre feeding each flat through a Heat Interface Unit. If your radiators are cold and you’re in one of these blocks, the source of heat is the shared network, and a loss of heat or hot water usually routes to the managing agent or heat supplier — not a heating engineer.

What can still be your side of the line is the pipework, radiators and valves inside the flat, depending on your lease and heat-supply agreement. A verified heating engineer can bleed radiators, replace a leaking valve or trace an internal leak — but they can’t and shouldn’t touch the HIU or the network. If you’re unsure what you have, that’s the first thing to establish before booking a repair.

Power flushing, filters and inhibitor — done properly

When sludge has built up, the recognised cleaning methods under BS 7593:2019 include power flushing, mains-pressure cleaning and gravity cleaning. A power flush pushes cleaning chemicals through the system at high flow to lift and remove magnetite and scale; it’s the most thorough option for a badly sludged Woolwich system with multiple cold radiators. It isn’t right for every system, though — on very old or fragile pipework, or radiators with severe internal corrosion, a gentler clean may suit better, and a flush won’t rescue a radiator that’s already corroded through.

After cleaning, three things protect the system for the future: a permanent in-line magnetic filter to catch new debris, a dose of corrosion inhibitor, and an annual water test to check the inhibitor is still doing its job. Skipping the filter or the inhibitor is a false economy in hard-water Woolwich, because the sludge simply comes back. If you’re weighing up whether an ageing boiler is worth another repair once the system’s clean, our combi vs system boiler guide (/london/guides/combi-vs-system-boiler-uk/) and the wider London hard water guide (/london/guides/london-hard-water-guide/) are useful reading, and knowing where your stop tap is (/london/guides/find-your-stop-tap/) helps in any leak.

Council tenants and leaseholders: the Royal Greenwich route

If you rent from Royal Greenwich, heating repairs go through the council, not a private firm. Royal Greenwich treats loss of heating and hot water seriously: its repair-response timescales (source) list winter loss of heating or hot water, loss of gas supply, and a blocked flue to a boiler among its urgent one-working-day categories, and a leaking heating pipe, tank or cistern is treated urgently too. Council tenants who’ve lost heating or hot water should call Royal Greenwich on 020 8921 8900.

Leaseholders sit differently: Royal Greenwich states that leaseholders are generally responsible for the heating and hot-water systems and pipework inside their own home, while the council looks after the structure, communal areas and shared services. So a leaseholder usually arranges their own internal heating repair, but shared pipework and plant may sit with the council, freeholder or managing agent. Check before you book — the boundary is rarely where people assume.

Central heating repair in Woolwich — FAQs

Sources

Thames Water — hard water: https://www.thameswater.co.uk/help/water-and-waste-help/water-quality/hard-water

BSI — BS 7593:2019 code of practice (domestic scope; clean/flush, inhibitor, filter, annual test): https://knowledge.bsigroup.com/products/code-of-practice-for-the-preparation-commissioning-and-maintenance-of-domestic-central-heating-and-cooling-water-systems

HSE — who can do gas work / ‘wet work’ boundary: https://www.hse.gov.uk/gas/landlords/safetycheckswhocan.htm

Gas Safe Register — find/check an engineer: https://www.gassaferegister.co.uk/find-an-engineer-or-check-the-register/

SSE Energy Solutions — Royal Arsenal Riverside HIU / district heat: https://www.sseenergysolutions.co.uk/news-and-insights/case-studies/royal-arsenal-riverside-woolwich

Royal Borough of Greenwich — repair response times; leaseholder responsibilities: https://www.royalgreenwich.gov.uk/housing/request-repair/how-long-it-takes-repair-problem

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Last reviewed: May 2026 by Adiel Khan — SFEDI-accredited business advisor, 20+ years’ experience (South East Enterprise Ltd) and operator of VerifiedPlumbers. LinkedIn ↗