London does flats in two very different styles. There's the red-brick mansion block, all brass letterboxes, creaky lifts and a boiler room that's older than most of the residents. And there's the glass tower, with a concierge desk, a heat network and a lift that talks to you. Both are full of thermostatic mixing valves, and both have hot water systems that change how those valves behave.
Mansion blocks: communal hot water from the basement
Many London mansion blocks, especially in places like Maida Vale, Marylebone, Kensington and Bloomsbury, still have central hot water. A plant room in the basement heats and stores water, and a circulation loop carries it up through the building and back again, so there's hot water at every flat without a long wait.
This works well when it's working. When it isn't, every TMV in the building gets the blame:
- The far end runs cool. If the circulation loop isn't balanced, flats furthest from the plant room get cooler hot water. Their TMVs can't deliver the set temperature because they don't have hot enough water to mix with.
- Morning rush hour. At 7.30am everybody showers at once and an undersized or tired plant struggles. In winter, with colder mains, it's worse. We covered this in winter cold water and your TMVs.
- Legionella control. HSG274 Part 2 expects hot water to reach outlets at 50°C or more within a minute, and the return to the plant to be at least 50°C. If parts of the loop run cool, that's a Legionella issue as well as a comfort one, and it's worth flagging to the building's risk assessor.
So in a mansion block, we check the supply temperatures at the valves as well as the valves themselves. If the problem is upstream, we'll say so, and you won't be paying for new cartridges that won't help.
High-rises: heat networks and boosted water
Newer towers, such as those around Canary Wharf, Stratford, Nine Elms and the Royal Docks, often work differently. Many are on a communal heat network. Each flat has a heat interface unit (HIU) that takes heat from the network and makes hot water on demand. Others have central plant with a circulation loop like a mansion block, just a lot taller.
Either way, two things matter for TMVs:
- Pressure. Water has to be pumped up a tall building, so blocks are split into pressure zones and supply pressures vary floor by floor. A TMV needs to suit the pressures it's actually getting, and the hot and cold supplies should be reasonably balanced. That's where the BS EN 1111 (high pressure) and BS EN 1287 (low pressure) approvals come in.
- Hot water from an HIU. Instantaneous hot water can vary with demand and with how the HIU is set up. If a flat's bath TMV is wandering, the HIU settings and its own maintenance are worth a look before blaming the valve.
Where the TMVs are in a London flat
In flats built or converted in the last couple of decades, Building Regulations Part G means bath hot water is limited to 48°C, and a TMV under the bath is the usual way to do it. Some flats have them on basins and showers too, and thermostatic shower mixers do the same job. In older mansion flats, valves often turn up wherever the last refurbishment put them, including behind tiles with no access at all.
Whose valve is it? In leasehold blocks, a TMV inside a flat may be the leaseholder's responsibility, the freeholder's or the managing agent's, depending on the lease. Worth checking before planning a building-wide programme.
Servicing a whole block without chaos
- Start with the plant. Get readings from the plant room and the return before the flats, so you know what each valve has to work with.
- Work floor by floor, usually top down in a tower so the lift does the hard work early.
- Send resident letters with the date, a time window and a number to rearrange. Our post on planning around parking and access goes into this.
- Record everything in one register, flat by flat, with access notes for next time.
- Plan the replacements. Obsolete valves, wrong pressure ratings and tiled-in valves go on a priced list rather than being dealt with in a panic.
A typical scenario
Imagine a 1920s mansion block in Maida Vale with communal hot water and a TMV under every bath. Residents on the top floor complain of tepid baths every winter, and the managing agent has had two of the valves replaced already without much change. On a visit like that, we'd take readings at the plant, on the return and at the affected flats. If the hot water arriving upstairs is well below where it should be, the next call is to the plant engineer about balancing the loop, not to us for more cartridges. We'd still service the valves, because London's water will have scaled them, and we'd flag any without proper access for a panel at the next refurbishment.
Valves that need replacing
Mansion blocks often have valves from refurbishments decades ago, some long out of production. Towers sometimes have valves that were chosen at design stage and never quite suited the pressures they ended up with. Either way, our installation and replacement service fits the right valve for the supply and the outlet, commissions it and adds it to your register.
Where we work
We service mansion blocks and towers right across the capital, from the red-brick streets of Central London to the new towers of East London. For more on what London water does to these valves, see hard London water and TMV limescale.
The short version
In flats with shared hot water, the valve is only half the story. Check the supplies, plan the building floor by floor, keep one register and deal with replacements properly. Then the top floor gets warm baths, and nobody's paying for cartridges they didn't need.
See TMV servicing for what each visit includes.
Got TMVs in London that need a look?
Tell us roughly what you've got and where. We'll give you a fixed quote and a date that works around your building.