Boilers & Heating
Boiler repair
TL;DR
About 70% of "broken" boilers are fixed on the first visit for under £250 — most commonly a stuck diverter valve, a failed expansion vessel, or a blocked condensate. The £50 diagnostic tells you exactly what's wrong and how much it will cost to fix, so you don't get sold a new boiler you don't need.
A boiler that's ten years old and locked out on F22 doesn't automatically need replacing. It probably needs a new pressure switch, or a top-up loop that's been left cracked open, or a heat exchanger that's silted up with black iron oxide from a system that never got a filter. All three of those are repairs, not replacements.
This page explains how we approach a boiler repair, the most common faults we see in the North West, honest indicative pricing, and — critically — when we'll actually tell you to stop spending money on it and replace instead.
Fixed £50 diagnostic
Flat fee. No hourly meter running.
Fair quote or refund
Transparent pricing — refunded if we don't fix it.
Vetted UK engineers
DBS-checked, insured, real reviews.
AI-triaged in seconds
KJ chats first so the right engineer arrives.
What should I do before you arrive?
Safety first: if you can smell gas at any point, leave the property and call the National Gas Emergency Service on 0800 111 999. Not us — them. Everything below assumes the boiler is faulty but not leaking gas.
- Note the fault code on the display (F22, E133, EA — whatever it says)
- Check the pressure gauge — is it under 1 bar or over 2.5?
- Check for water under the boiler, on the pipework, or at the pressure relief outside
- Check the condensate pipe outside is not frozen (common Nov–Feb in the North West)
- Turn heating on and off — is the fault immediate or does it take five minutes?
What are the ten most common boiler faults?
After thousands of jobs, the same handful of faults account for the majority of callouts. In rough order of what we see week-in, week-out across Rochdale, Manchester and Bolton:
- Diverter valve stuck (hot water fine, no heating, or vice versa)
- Expansion vessel lost its pre-charge (pressure creeps up when heating fires)
- PCB fault or dry joints on the main board (intermittent lockouts)
- Fan failure (three flashes, no ignition, boiler audibly clicks then stops)
- Blocked or leaking heat exchanger (kettling noise, drops in efficiency)
- Condensate frozen or blocked (Ea/EA on Worcester, F1E on Ideal)
- Low pressure (below 1 bar — often a leak on the system, not the boiler)
- Ignition electrode or ignition lead breaking down (spark visible, no light-off)
- Gas valve fault (rarer, more expensive)
- Air pressure switch failure (common on older Baxi and Ideal)
How do you decide whether to repair or replace?
There's no honest single answer, but there is an honest framework. We use three rules and we tell you which one applies before we quote:
Rule 1 — Age. Under 8 years old, repair almost always wins. 8-12 years, it depends on the fault. Over 12 years and a major component (heat exchanger, gas valve, PCB) has failed, replacement usually makes sense.
Rule 2 — Cost of the repair as a percentage of a new install. If the repair is under 30% of a straight swap, repair. Over 50%, replace. In between, we look at rule 3.
Rule 3 — Parts availability. If the manufacturer no longer stocks the part and we're relying on grey-market spares, we'll say so and recommend replacement even if the repair itself is cheap.
Are you Gas Safe registered?
Every engineer who touches a gas appliance on a KJ Plumbers job is Gas Safe registered — no exceptions, no "apprentice supervising themselves". You'll be shown the ID card at the door and the registration number is on every invoice. Anyone working on gas without a valid Gas Safe registration is committing a criminal offence under the Gas Safety (Installation and Use) Regulations 1998.
What guarantee do you give on the repair?
Every part we fit carries a 12-month guarantee on parts and labour. If the same fault returns within 12 months on the same part, we come back at no cost. If the repair we diagnosed doesn't fix the fault, the £50 diagnostic is refunded in full — no arguments.
Typical prices
Real-world ranges from recent Northwest jobs. Your final price is confirmed in writing before any work starts.
| Item | Typical price | Notes |
|---|---|---|
| Diagnostic visit (deducted from repair) | 50 | Written diagnosis + fixed quote |
| Diverter valve replacement | 180 – 320 | Part + labour, most brands |
| Expansion vessel replacement or re-charge | 120 – 260 | Re-charge sometimes enough |
| PCB replacement | 260 – 480 | Genuine OEM board |
| Fan replacement | 220 – 380 | Includes fan gasket + test |
| Ignition electrode + lead | 110 – 180 | Common on 5-10 yr boilers |
| Condensate unblock / re-route | 90 – 180 | Insulation added if external |
| Gas valve replacement | 380 – 620 | Full commissioning after fit |
| Full heat exchanger replacement | 550 – 900 | Repair vs replace decision point |
| Full boiler swap (for comparison) | 2,200 – 3,800 | See boiler installation page |
Which brand should you fit?
We hold Worcester Bosch, Vaillant, Ideal and Baxi common parts on the van (PRVs, expansion vessels, diverter cartridges, ignition leads), so most first-visit repairs are done in one trip. For proprietary boards or gas valves we usually source next-day from a UK distributor. We install and service Worcester Bosch, Vaillant, Ideal, Baxi, Viessmann and Alpha — none of them pay us commission and we don't push a "boiler of the month".
Our promise on this job
Flat £50 diagnostic — deducted in full from any work booked. Fair, transparent quote before we start. If we can't fix the fault we diagnosed, we refund the diagnostic. All gas work is signed off by a Gas Safe registered engineer.
Talk to KJ about boiler repair
Real triage in seconds. £50 diagnostic visit — refunded if we don't fix it.