No hot water in a mansion block flat

Mansion blocks are a London institution. Red brick or stone, built mostly from the 1880s to the 1930s, with porters, lifts and grand stairwells. Many still run hot water from a single plant room in the basement. When that fails, every flat feels it. When only your flat goes cold, the fault is usually closer to home.

How communal hot water works

In a block with communal hot water, one set of boilers and cylinders, or a heat source, in the basement plant room heats water for the whole building. The hot water travels up through risers, the vertical ducts that carry pipes past each floor, and a branch serves each flat.

Some blocks send stored hot water straight to every tap. Others send heat to a heat interface unit in each flat, a small box that uses the building’s hot water to heat your own. Some flats have their own cylinder heated by the communal system.

Is it the building or just you?

What you see	Likely cause	Who to contact
No hot water in any flat	Plant room fault, pump failure	Porter or managing agent
No hot water on upper floors	Circulation pump or air in the riser	Managing agent
Only your flat is cold	Your valve, heat unit or cylinder	Plumber, or landlord if you rent
Only one tap or shower is cold	Mixing valve or isolation valve at that fitting	Plumber
Hot water is lukewarm everywhere	Plant struggling or set too low	Managing agent

Ask a neighbour on your floor and one on another floor. That answers most of it.

Mansion blocks in Westminster

Westminster has the second highest share of purpose built flats of the boroughs we cover. In the 2021 Census, 70.2% of households lived in purpose built flats (Nomis, TS044), including the mansion blocks of Marylebone, Maida Vale and St John’s Wood. Many of these blocks have been partly modernised over the years, so you may find a modern plant room feeding old pipes in the risers, or flats that have opted out of the communal system with their own boilers.

That mix is why it pays to know how your own flat is set up. Your lease, the managing agent or the porter can usually tell you.

Who is responsible

The Leasehold Advisory Service says the freeholder is usually responsible for communal pipes, water tanks and boilers that serve more than one flat. In a mansion block, that normally includes the plant room and the risers. The pipes and equipment serving only your flat, such as a heat interface unit or a cylinder, are usually your responsibility as a leaseholder. Check the lease, because some leases treat these differently.

If you rent, section 11 of the Landlord and Tenant Act 1985 requires landlords to keep the installations for heating water in repair. Shelter notes this can include installations a landlord owns or controls that serve the dwelling, such as communal heating in a block owned by the same landlord.

What to check in your flat

If neighbours have hot water and you do not:

1. Check your isolation valves. There may be valves on the hot water branch into your flat, often in a cupboard near the front door or in the kitchen.
2. Check any heat interface unit. Look for a display, an error light or a power switch. Check that it is on.
3. Check a cylinder, if you have one. Is the immersion heater on? Is the cylinder warm?
4. Check mixing valves. Showers and some basins have thermostatic mixing valves. If only one fitting is cold, its cartridge may have failed. London’s hard water does not help: Thames Water says all water in its region is hard, and scale is a common cause of sticking cartridges.

What a plumber can do

A plumber can deal with the water side in your flat: valves, cylinders, mixing valves, leaks and pipework. Many heat interface units have a manufacturer’s service arrangement, so check before anyone opens one up. The plant room is usually maintained by the freeholder’s own contractor.

Any work on a gas boiler, communal or private, must be done by a Gas Safe registered engineer. Ask to see their ID card and check it on the Gas Safe Register.

When to treat it as urgent

No hot water is not usually an emergency on its own. Treat it as urgent if:

• someone vulnerable relies on hot water for washing or medical needs
• it comes with a leak, for example from a heat unit or cylinder
• the heating has gone off too in cold weather

Report building wide faults to the porter or managing agent straight away, and in writing. Our no water or no hot water page explains what a visit to your flat involves, and our guide to no hot water when the heating works covers flats with their own boiler.