Boiler Repairs
In London — Diagnosed
Properly, Fixed Once.
Faulty pressure, no hot water, F-code on the display, kettling noises, radiators cold at the top? A Gas Safe engineer arrives, diagnoses the actual fault, and quotes a fixed price before we start replacing parts. No blind-swap 'diagnostic' bills. 12-month guarantee on the labour.
What a proper boiler repair actually looks like.
A boiler repair should start with a diagnosis, not a parts order. The most expensive mistake homeowners make is calling a firm that charges to swap a PCB, then a diverter valve, then a pump — until one of them happens to fix it. You pay for all three plus labour. We arrive with an analyser, a multimeter and a service manual, and we tell you what's actually wrong before you agree to spend anything.
Chelsea Plumbing & Heating Co. repairs all major domestic boiler brands — Worcester Bosch, Vaillant, Baxi, Ideal, Alpha, Viessmann, Glow-worm, Potterton and more. Combi, system and regular. Owner-led by Ian Fisher with many years in the trade and full Gas Safe registration (Reg. 952303).
This service is for anyone with a fault code on the display, no heating, no hot water, low or dropping pressure, banging or kettling noises, leaks from the boiler casing, or a boiler that keeps locking out and needing a reset. It's also for landlords whose tenant has reported a fault and needs a compliant repair with paperwork.
Repair or replace? If your boiler is under 8 years old and the fault is a single component, repair is almost always the answer. If it's 12+ years old and you've had two or more callouts in the last two years, we'll be honest with you at the quote stage — sometimes a new install pays back inside three winters on energy savings alone.
Why 'leaving it a few days' turns £150 into £1,500.
A dropping pressure gauge means a leak somewhere in the system — often a pinhole on a radiator valve, a failed auto-air-vent, or an expansion vessel losing charge. Left running, the boiler keeps trying to fire against low pressure, kills its pump, and eventually cracks the heat exchanger. A £120 vessel recharge becomes a £700 heat exchanger becomes a new boiler.
Kettling, banging and gurgling noises are almost always sludge in the primary circuit. Ignore them and the boiler runs progressively hotter on the same demand, wastes gas, and shortens the appliance life. A £450 powerflush is a fraction of a new heat exchanger — and a tiny fraction of a new boiler.
A fault code that clears with a reset button is telling you the boiler nearly went into permanent lockout. Reset it enough times and you'll turn a diagnosable, fixable fault into a mystery intermittent that needs multiple visits to isolate.
- ×Topping the boiler pressure up daily instead of finding the leak — burns out the filling loop and hides the real fault.
- ×Ordering parts online and asking a 'handyman' to fit them — invalidates any warranty and often damages related components.
- ×Ignoring an F-code and repeatedly resetting — turns a single-fault repair into a multi-visit diagnostic job.
- ×Leaving a leaking pressure-relief pipe (the copper pipe exiting the wall outside) — it's telling you the expansion vessel or PRV needs attention now.
- ×Buying a boiler cover plan that excludes 'pre-existing faults' after you've already noticed the symptom — you'll be turned away on the first callout.
- ×Bleeding radiators when the real fault is a failed pump or seized motorised valve — pressure drops, symptoms return, nothing fixed.
A methodical system,
not a rushed callout.
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01Triage callWe take the symptoms, fault code, boiler make/model and age over the phone — often we can hint at the likely fault before we arrive.
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02On-site diagnosisAnalyser, multimeter, pressure gauges and manufacturer service data — actual diagnosis, not part-swapping.
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03Fixed quoteWritten price for the repair before we proceed. Parts + labour. No hidden extras.
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04Repair & testParts fitted, system re-pressurised, flue-gas analyser reading taken, controls tested through a full cycle.
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0512-month guaranteeWritten 12-month workmanship guarantee on the labour, plus manufacturer warranty on any new parts.
Concrete outcomes,
not vague promises.
Fixed within one visit
Van stocked with the common failure parts for major brands — pumps, diverter valves, PRVs, expansion vessels, fans, PCBs, sensors.
No blind part-swapping
You only pay for the part that actually fixed the fault — diagnosed with a manufacturer's fault-flow, not guessed.
Gas Safe signed off
Every gas repair is carried out by a Gas Safe registered engineer (Reg. 952303) and re-tested with a flue-gas analyser before we leave.
Out-of-hours cover
Genuine no-heat/no-hot-water emergencies covered outside standard hours at £150/hr — no premium mark-up on parts.
Honest repair-or-replace advice
If a repair isn't the right answer, we'll tell you at the quote stage — with the numbers to prove it.
Written 12-month guarantee
Workmanship covered for a year. If the same fault returns on the same component within 12 months, we come back at no charge.
Photographs from
actual jobs.
Real installations, repairs and diagnostics carried out by Ian across London and the Home Counties. No stock photography.
Common boiler faults we repair every week.
Most boiler faults come from a small pool of recurring failure points. Here are the ones we see most often across combi, system and regular boilers in London properties.
Low or dropping pressure
Almost always a system leak — pinholes on radiator valves, failed auto-air-vent, faulty PRV, or expansion vessel losing charge. We pressure-test, isolate and repair rather than just topping up.
No hot water but heating works (combi)
Usually a failed diverter valve, a stuck flow sensor, or a scaled plate heat exchanger. Diagnosed by isolating flow and testing electrical continuity — not by swapping all three.
F/E/A fault codes
Every brand has its own fault-code library. F22 on a Worcester is low pressure. F75 on a Vaillant is pump/pressure sensor. We reference the manufacturer's service manual on every visit — no guessing.
Kettling, banging, whistling noises
Almost always limescale on the heat exchanger or sludge in the primary circuit. Powerflush + inhibitor + magnetic filter is the fix — patching over it with descaler tablets rarely holds.
Cold radiators / cold at the top
Cold at the top is air (bleed). Cold at the bottom is sludge (flush). Cold entirely on some rads but not others is usually a balancing or motorised-valve issue.
PRV / discharge pipe dripping outside
Overpressure discharge — the boiler is telling you the expansion vessel has lost its charge, or the PRV itself has stuck. Both are same-visit fixes if diagnosed properly.
Fan, PCB, ignition and flame-failure faults
Electronic faults need a multimeter and a service manual, not part rotation. We carry replacement PCBs and fans for the most common Worcester, Vaillant, Baxi and Ideal ranges.
Landlord repair visits
For let properties we work with your letting agent, provide a tenant-facing incident report, and reissue the CP12 if the repair affected the gas certification.
How much does a boiler repair cost in London?
Our standard rate is £90/hr Mon–Fri 8–5. Most single-fault repairs (diverter, pump, PRV, expansion vessel, sensor) are completed in one visit including parts. Out-of-hours cover is £150/hr. We give you the fixed price after diagnosis before we replace anything.
Do you charge a call-out fee?
No standalone call-out fee — you're charged the standard hourly rate from the point Ian arrives on site. Diagnosis is usually completed within the first hour, and the fixed repair quote is given before we proceed.
Can you come out today?
Same-day cover for no-heat and no-hot-water calls is often possible, particularly for out-of-hours emergencies at £150/hr. Call 07801 550790 to check availability.
Do you repair all boiler brands?
Yes — Worcester Bosch, Vaillant, Baxi, Ideal, Alpha, Viessmann, Glow-worm, Potterton, Ariston, Ferroli and more. Van is stocked with the common failure parts for the mainstream ranges.
What guarantee do I get on a repair?
12 months on the workmanship, in writing. New parts carry the manufacturer's own warranty on top (typically 12–24 months).
Is it worth repairing an old boiler?
If your boiler is under 8 years old, almost always yes — a single-component repair keeps a good appliance running. If it's 12+ years old and you've had multiple callouts recently, we'll give you a straight repair-vs-replace comparison at the quote stage.
Will you condemn my boiler?
Only if it is genuinely unsafe under Gas Safe regulations (immediately dangerous or at-risk classification). If we do, you'll get a written report explaining exactly why and what needs to happen next.
What if the fault comes back?
If the same fault on the same component recurs within 12 months, we return and re-fix at no additional labour charge. New parts remain covered by their own manufacturer warranty.
Do you cover landlord boiler repairs?
Yes — we work with individual landlords and letting agents across London, provide a tenant-facing report on every visit, and reissue the CP12 gas certificate where the repair affects gas compliance.
Can you fix a boiler that's already been condemned?
Often yes, if the condemning issue is repairable (blocked flue, faulty gas valve, high CO reading traceable to a specific component). If the appliance itself is beyond economical repair we'll tell you at diagnosis.
Fixed price. Gas Safe.
12-month guarantee.
Free estimates from Ian directly — no call centre, no subcontractors, no surprise bills. One point of contact from first call to twelve-month follow-up.