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0207 046 1363
ERLEMERGENCY REPAIRSLONDON
Gas Safe engineer repairing a combi boiler for no hot water in a London flat
Gas Safe Registered • Same Hour 24/7

No Hot Water Repair London

Cold tap on a freezing morning? Gas Safe engineer at your door within the hour, 24/7 across London. Diagnosis £95–£140, diverter valve £180–£280, immersion £180–£280, cylinder stat £110–£170. Fixed written price before any repair starts.

70% of no-hot-water calls fixed on the same visit from van stock. 12-month workmanship guarantee on every repair.

0207 046 1363WhatsApp 07456 975436Book online

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Gas Safe RegisteredG3 Unvented Qualified£5m Public Liability (Hiscox)12-Month Workmanship Guarantee24/7 Same-Hour Dispatch
Quick Answer

Most no-hot-water calls in London are caused by a stuck combi diverter valve (£180–£280), a failed motorised valve on an S-plan or Y-plan system (£160–£260), or an immersion / cylinder thermostat fault (£110–£280). A Gas Safe engineer attends within the hour 24/7, isolates the fault, gives a fixed written price, and fixes around 70% on the same visit from van stock.

What causes no hot water?

"No hot water" is a symptom, not a fault. The underlying causes split cleanly by system type. On a combi boiler — where the boiler makes hot water on demand without a cylinder — the prime suspect is almost always the diverter valve, a small brass spool valve that switches the boiler's heat exchanger between heating mode and hot water mode. When the diverter sticks closed on the heating side, the radiators heat but the tap stays cold. The next suspects on a combi are the flow sensor (the boiler doesn't know you've opened the tap), the secondary plate heat exchanger (scaled up in hard-water boroughs), and the PCB.

On a system or regular boiler with a separate hot water cylinder, the diagnosis is different. The boiler fires fine for heating, which proves the gas, fan, pump and PCB are alive — so the fault is downstream, in the controls or the cylinder itself. The most common culprits are the motorised valve (2-port on an S-plan, 3-port mid-position on a Y-plan), the cylinder thermostat, the immersion heater (when used as backup), and on unvented systems the high-limit thermal cut-out that needs resetting after a one-off overheat.

Thermal stores and heat-pump systems add a third group of faults — primary circulator pumps, plate heat exchangers and three-way valves on the buffer side. All of these are routine for our engineers. The diagnostic process is the same: temperature checks at the boiler flow and return, at the cylinder primary and secondary, and at the tap. The numbers tell you exactly where the heat is being lost.

What we cover

Every common no-hot-water fault on every common London system type. If your property has it, our engineers fix it.

  • Combi boiler diverter valve diagnosis — heating-only-but-no-hot-water symptom
  • Pilot light relight and thermocouple replacement on older open-flue boilers
  • Immersion heater test and swap on vented and unvented cylinders
  • Unvented cylinder thermostat and high-limit stat replacement (G3 qualified)
  • Motorised valve (2-port and 3-port mid-position) head and body replacement
  • Heating pump (Grundfos UPS/Alpha, Wilo Yonos) diagnosis and swap
  • Thermal store coil flow and return fault investigation
  • Cold mains pressure check at incomer for combi flow-rate complaints
  • Expansion vessel pre-charge check on unvented and sealed systems
  • Power and PCB fault diagnosis where the boiler fires but no DHW
Engineer diagnosing a hot water fault on a combi boiler in a London kitchen

Hot water repair cost in London

Pricing is by fault type, not by boiler brand. A fixed written price is given on the doorstep before any repair starts, so you authorise the work knowing the final cost. No surprise add-ons, no inflated parts mark-ups, no compulsory annual service tied to a one-off repair.

Repair TypeWhat's CoveredTypical Cost
Diagnosis call-out (first hour)Engineer attends, isolates fault, written diagnosis. Daytime weekday band.£95–£140
Diverter valve replacementCombi boiler diverter swap, system flush of valve body, hot/cold function test.£180–£280
Immersion heater replacementElement swap on vented or unvented cylinder, new gasket, thermostat check.£180–£280
Cylinder thermostat replacementUnvented or vented cylinder stat swap, temperature calibration, recovery test.£110–£170
Motorised valve replacement2-port or 3-port mid-position valve swap, head and body, wiring re-termination.£160–£260
Pilot light / ignition fault repairPilot assembly, thermocouple or igniter swap on older system boilers.£130–£220
Pump replacement (heating / DHW)Grundfos / Wilo circulator swap, isolation valves, bleed, balance and re-pressurise.£220–£340

* Prices include VAT and parts on standard van-stock items. Out-of-hours band quoted on the phone before dispatch. Full pricing list on the pricing page.

How it works — call to fix in four steps

1

Call and triage in under 2 minutes

Phone the landline 0207 046 1363 or WhatsApp 07456 975436. The controller asks four questions: boiler make, age, error code on display, and whether the heating still works. That tells us 80% of the diagnosis before we leave the depot.

2

Same-hour engineer dispatch

A Gas Safe registered engineer is dispatched from the nearest depot — Central, North, South or East London — typically arriving within 60–90 minutes 24/7. ULEZ-compliant van stocked with diverter valves, motorised valves, immersion elements and pumps for same-visit fix.

3

Diagnosis and fixed-price quote

On arrival the engineer isolates the fault — combi diverter, motorised valve, cylinder stat, immersion, pump or PCB — and gives a fixed written price before any repair starts. You authorise, we fix. No surprise add-ons after the fact.

4

Repair, test and certificate

Repair carried out the same visit in around 7 cases out of 10 from van stock. Full hot/cold function test, temperature reading at the tap (must reach ≥55°C at the cylinder outlet), and a written invoice with engineer Gas Safe number, parts fitted and 12-month workmanship guarantee.

ULEZ-compliant engineer van stocked with diverter valves and motorised valves for same-day London hot water repairs

Unvented cylinders — the G3 requirement

Unvented hot water cylinders — Megaflo, Telford Tempest, Range Tribune, Heatrae Sadia Megaflo, Joule and similar mains-pressure stored hot water systems — operate under significant pressure and are governed by Part G of the Building Regulations. Any work on the safety-critical components (thermostat, high-limit cut-out, expansion vessel, temperature & pressure relief valve, tundish) must by law be carried out by an engineer holding a current G3 unvented hot water qualification.

Every hot water engineer dispatched holds a current G3 ticket alongside Gas Safe registration and the Water Regulations 1999 (WRAS) approval. Cylinder thermostat replacement is £110–£170 fitted, with calibration to the BS EN 12897:2016 standard temperature band of 60–65°C at the cylinder outlet for legionella control.

Unvented hot water cylinder being serviced in a London airing cupboard

Areas covered

Same-hour hot water repair attended across all 32 London boroughs and the City of London, 24/7. Highest call volumes from Camden, Westminster, Islington, Hackney, Tower Hamlets, Southwark, Lambeth and Wandsworth.

CamdenWestminsterIslingtonHackneyTower HamletsSouthwarkLambethWandsworth

Frequently Asked Questions

Why have I got central heating but no hot water?
On a combi boiler this is almost always the diverter valve — a brass valve inside the boiler that switches flow between the heating circuit and the hot water heat exchanger. When the diverter sticks closed on the heating side, the radiators heat up but the hot water tap stays cold. Replacement is around £180–£280 including parts, typically a 60–90 minute job on the same visit. On a system or regular boiler with a cylinder, the same symptom usually points to a failed motorised valve (the 2-port DHW valve or the mid-position 3-port valve) rather than the boiler itself.
How much does hot water repair cost in London?
Diagnosis call-out is £95–£140 in the weekday daytime band, with a written fixed price given before any repair begins. Common repairs sit in known ranges: diverter valve £180–£280, immersion heater £180–£280, cylinder thermostat £110–£170, motorised valve £160–£260, pilot light or thermocouple £130–£220, pump replacement £220–£340. Out-of-hours (evening, weekend, bank holiday) attracts a higher call-out band — quoted on the phone before dispatch.
Can you fix no hot water the same day?
Yes. Around 70% of no-hot-water calls in London are fixed on the same visit from van stock — diverter valves, motorised valves, immersion elements, thermostats and the most common circulator pumps are carried as standard. Same-hour dispatch is available 24/7 including weekends and bank holidays. The remaining 30% — burnt PCBs, manufacturer-specific gas valves, immersion thermostats on older imported cylinders — usually need a part ordered next-day for return fit.
What if my pilot light has gone out and won’t relight?
On older open-flue and back-boiler systems a pilot that will not stay lit is almost always a failed thermocouple — the safety probe that senses the pilot flame and holds the gas valve open. A new thermocouple is £130–£220 fitted including the labour to drop the burner assembly. If the pilot will not even strike, the spark electrode, piezo or gas valve solenoid is the next suspect. We do not attempt to relight a pilot on a boiler that has failed for an unknown reason without isolating and testing the gas valve first — safety comes first under Gas Safe procedure.
How do I know if my immersion heater has failed?
Three classic signs: lukewarm water that never gets properly hot, an immersion that runs constantly without ever shutting off on the stat, or a tripped RCD when the immersion switch is turned on. The diagnostic is an insulation resistance test on the element with an insulated screwdriver and a multimeter at the element terminals. Replacement is £180–£280 fitted, including a new gasket and a temperature recovery test. We carry both 11-inch and 14-inch elements for the most common Megaflo, Telford and Range cylinders.
Is unvented cylinder work different from a vented one?
Yes, significantly. Unvented hot water cylinders (Megaflo, Telford Tempest, Range Tribune, Heatrae Sadia Megaflo) operate at mains pressure and store stored hot water under pressure. Any work on the cylinder itself — thermostat, high-limit stat, expansion vessel, T&P relief valve — must by law be carried out by an engineer holding the G3 unvented qualification. All our hot water engineers hold a current G3 ticket. A standard vented (gravity) cylinder with a header tank in the loft does not need G3, but the rest of the diagnostic process is the same.
Could it be the motorised valve rather than the boiler?
On any S-plan or Y-plan system (a boiler plus separate hot water cylinder) — yes, this is the single most common cause of "heating works, hot water doesn't" calls. An S-plan uses two separate 2-port valves (one for heating, one for hot water). A Y-plan uses a single mid-position 3-port valve. When the DHW valve's motor seizes, the boiler fires for heating but nothing diverts flow through the cylinder coil. Replacement is £160–£260 — usually just the valve head, sometimes the full body and head if the valve body is corroded. We carry Honeywell, Drayton and Tower of London compatible spares on the van.
What about a thermal store — why is the hot water still cold?
A thermal store stores heated primary water and uses a plate heat exchanger or internal coil to make the domestic hot water on demand. The two common faults are a failed circulating pump on the primary side (the boiler heats the store, but the store doesn't transfer to the tap), and scaling of the plate heat exchanger in hard-water London boroughs (the store is hot, but the tap is barely warm). Diagnosis is a flow and return temperature check at the store outlets, then a flow-rate measurement at the tap. Repair is either a new pump, a plate heat exchanger swap, or a system flush of the secondary side.
Can a tripped fuse or power cut cause no hot water?
On a fully gas-fired combi or system boiler the boiler itself needs a 230 V supply for the PCB, fan and pump — so a tripped fused spur or RCD knocks out the hot water entirely. On a system with an electric immersion as backup, the immersion is on its own dedicated circuit and can be tripped independently. First check the boiler is showing a display, then check the immersion fused spur (usually a switch above the airing cupboard door). Any RCD that keeps tripping when reset points to a real fault — water in a junction box, a failed immersion element, or a burnt cable in the cylinder cupboard — and needs an engineer.
Do you cover weekends and bank holidays?
Yes. Same-hour 24/7 across all 32 London boroughs and the City of London, including weekends, bank holidays and Christmas Day. The out-of-hours call-out band is quoted on the phone before dispatch so there are no surprises. Engineers carry diverter valves, motorised valves, immersion elements, cylinder thermostats and the most common pumps on the van, so most weekend calls are fixed before Monday morning.

Get your hot water back today

Gas Safe engineer dispatched same hour 24/7. Fixed written price before any repair. 70% of calls fixed on the same visit from van stock. 12-month workmanship guarantee.

0207 046 1363WhatsApp 07456 975436Book online

Fully insured • Gas Safe number on every invoice • G3 unvented qualified • VAT-registered

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