Real 2026 London prices for the common repairs, what moves the number, and how to avoid overpaying.
The short answer
No hot water usually comes down to one of five causes: low boiler pressure, a controls or timer issue, a frozen condensate pipe, an ignition fault, or a failed diverter valve. Check pressure and controls yourself first; a diverter valve fault is the classic cause when heating works but hot water does not.
What the law requires
Why is there no hot water?
Hot water fails in two distinct patterns, and telling them apart does most of the diagnosis for you. Pattern one: no hot water and no heating either. The whole boiler is down, and the cause is whatever stopped it: pressure below the cut-off, a lockout code on the display, a tripped fuse, or in winter a frozen condensate pipe. Pattern two: heating works but hot water does not, or the reverse. The boiler itself is fine; the component that switches between the two jobs has failed, which on a combi is the diverter valve and on a system boiler is usually a motorised valve. Pattern two on a combi is one of the most common repairs in London, and it announces itself exactly this way.
The five-minute checks before you call anyone
Read the display. A fault code (Vaillant F22 or F28, Worcester EA, Baxi E133, Ideal F1 or L2) names the problem; look it up in our error code lookup on the homepage or the relevant guide.
Check the pressure gauge. Below 1 bar, repressurise to 1.5 bar via the filling loop; our boiler losing pressure guide has the full steps.
Check the controls. Thermostat calling for heat, hot water enabled on the programmer, and any smart control actually connected. Dead batteries in a wireless thermostat cause more “broken boilers” than any valve.
In freezing weather, check the external condensate pipe and thaw it if frozen.
Run a hot tap fully open for a minute. Combi boilers need a decent flow to trigger heating; a barely open tap, or a blocked tap aerator, can fool you into diagnosing the boiler.
Cold taps after the checklist? Describe the pattern on the phone and we will usually name the likely fault before dispatching. Call 020 3000 0000, same-day visits across London.
Heating works but no hot water: the diverter valve explained
No hot water in a system or conventional setup
If your home has a hot water cylinder, add three suspects: the motorised valve that routes boiler heat to the cylinder, the cylinder thermostat that asks for that heat, and, on many setups, an immersion heater that can serve as a temporary backup. If the immersion gives you hot water while the boiler route does not, the boiler-to-cylinder chain (valve, stat, or pump) is where the fault lives, and you have both a diagnosis and a stopgap while the repair is booked.
No hot water, quick answers
Why is my water lukewarm rather than cold?
On combis, usually a partially failed diverter valve or a scaled plate heat exchanger, common in London’s hard water; both are standard repairs.
Why does hot water cut in and out at the tap?
Flow-related: a combi needs sufficient flow to stay lit, so a weak main, a clogged tap or a failing flow sensor produces exactly this.
Can I get hot water while I wait for an engineer?
Cylinder households can use the immersion heater; combi households, being tankless, cannot, which is why we treat no-hot-water combi calls as same-day work.
How much does the repair cost?
The common fixes: diverter valve £180 to £350, motorised valve £150 to £280, plate heat exchanger descale or swap £150 to £320, thermostat work £90 to £200, all quoted fixed after diagnosis.