No Hot Water in London? The Fix Depends on Your Boiler Type -- Here's How to Tell

How to identify it

• Single unit on the wall -- no cylinder anywhere in the property
• Heats water on demand -- no stored hot water
• Usually in kitchen, utility room or airing cupboard
• No loft tank

How to identify it

• Wall-mounted boiler + large insulated cylinder (airing cupboard)
• Stores pre-heated water -- faster delivery to taps
• No cold water tank in the loft
• Immersion heater switch usually on cylinder

How to identify it

• Boiler + cylinder + cold water tank in the loft
• Oldest type of central heating system
• Gravity-fed -- water pressure from the loft tank
• Very common in Victorian and Edwardian London homes

The diverter valve switches boiler output between the heating circuit and the hot water circuit. When it sticks in the heating position, radiators get heat but taps get nothing -- or a brief burst of warmth then cold.

Symptom: Heating works normally; hot water absent or briefly warm then cold

London's water hardness (300mg/l+ calcium carbonate) deposits limescale inside the thin-plate heat exchanger that heats tap water on a combi. Scale narrows the channels, restricts flow and eventually blocks it entirely.

Symptom: Slow hot water flow that gets worse over months; eventually fails

Below 1 bar, most combi boilers cut out on safety and will not heat water or radiators. Check the pressure gauge on the front of the boiler. If below 1 bar, repressurise via the filling loop (the silver braided hose under the boiler).

Symptom: No heating and no hot water; pressure gauge below 1 bar

Some programmers and smart thermostats allow heating and hot water to be scheduled independently. If hot water has been switched off or set to a different schedule, the boiler will not heat water even though the heating works fine.

Symptom: Heating works; hot water absent at all times or only at certain times

The cylinder stat (usually a strap-on sensor on the side of the cylinder) tells the boiler when to heat the tank. Typically set to 60 degrees. If it fails, the boiler never receives the call to heat the cylinder.

Symptom: Cylinder is stone cold; boiler fires for heating but not hot water

A 2-port or 3-port motorised valve controls flow to the cylinder. When it sticks closed, hot water from the boiler cannot reach the cylinder even when the boiler is firing. The valve motor burns out over time -- very common on older systems.

Symptom: Cylinder stays cold; heating may still work via separate port

The immersion heater is an electric backup element inside the cylinder. If the primary (boiler) route fails, the immersion should still provide hot water. If the immersion has also failed, you lose all hot water. Check the red switch in the airing cupboard -- if the water stays cold after 45 minutes, the element has likely gone.

Symptom: No hot water even after switching on the immersion heater for 45+ minutes

Air trapped in the pipework to and from the cylinder can block flow completely or cause intermittent hot water. More common on older gravity-fed regular boiler systems. An engineer can clear an air lock by bleeding the circuit.

Symptom: Intermittent hot water; cold water from tap then suddenly warm; gurgling noises from cylinder

Heats water using its own internal element -- completely independent of the boiler. Works even when the boiler is broken. If you have an electric shower, use it normally.

If you have a cylinder (system or regular boiler), look for a red switch in the airing cupboard. Switch it on and wait 30-45 minutes. This heats the cylinder using electricity.

Note: immersion heaters draw 3kW -- expensive to run. Use for showers; don't leave on all day.

For basic hand washing and washing up. Not a shower solution, but covers the essentials while waiting for the repair.

Most London boroughs have at least one council leisure centre with public showers -- typically a few pounds for a swim + shower session. A practical option for same-day relief.