No Hot Water in London? 8 Things to Check Before Calling a Plumber

No Hot Water — Start Here

Hot water failures are one of the most stressful household problems. But before paying an emergency plumber callout fee, run through these eight checks — our engineers find that approximately a third of "no hot water" callouts are resolved by the homeowner before the engineer arrives.

1. Is It Just Hot Water, or Heating Too?

This single question narrows the problem significantly. If both heating and hot water are off, the boiler or gas supply has failed. If you have heating but no hot water (or vice versa), the problem is more likely in the distribution system — a diverter valve, cylinder thermostat, or programmer setting.

2. Check the Boiler Pressure (Combi Boilers)

Low pressure is the most common cause of no hot water with a combi boiler. Check the gauge — if it reads below 0.8 bar, repressurise the system using the filling loop and attempt a reset. Pressure should be 1-1.5 bar.

3. Check the Boiler Display for Fault Codes

If the boiler is showing a fault code, look it up. Common codes for hot water failure: Vaillant F.28/F.29 (ignition fault), Worcester Bosch EA 227 (ignition fault), Baxi E168 (ignition), Ideal F1/F2 (ignition). A single reset attempt is appropriate for ignition fault codes.

4. Check the Programmer and Thermostat

This sounds basic, but clock changes (BST/GMT), power cuts, and timer resets catch many people out. Check the programmer time and hot water schedule. On smart thermostats (Nest, Hive, tado°), check the app — the system may be in "off" mode or "away" mode.

5. Check the Hot Water Cylinder Thermostat (Gravity-Fed Systems)

Properties with a hot water cylinder (common in older London houses and maisonettes) have a cylinder thermostat that controls when the cylinder is heated. This thermostat can fail or be accidentally knocked to a very low setting. Check it is set to at least 60°C.

6. Check the Pilot Light (Older Boilers)

Older boilers with standing pilot lights can have the pilot extinguished by a draught. If you see a pilot light window on the boiler, check whether the small blue flame is present. Follow the boiler's instructions to relight — usually by holding the gas valve open manually while using a piezo igniter.

7. Check the Diverter Valve (Combi Boilers, Heating Works But Not Hot Water)

If your heating is working but you have no hot water from a combi boiler, the diverter valve — which switches the boiler's output between heating and hot water — may be stuck in the heating position. A sticking diverter valve is a common fault in older combi boilers and requires an engineer to repair.

8. Check the Immersion Heater (Cylinder Systems)

If you have a hot water cylinder with an immersion heater (an electric backup), check whether it is switched on and whether its circuit breaker has tripped. Immersion heaters provide hot water independently of the boiler — useful as a temporary measure while arranging boiler repair.