Worcester Bosch Boiler Repair: Faults and Costs

Worcester Bosch is one of the most widely fitted boiler brands in the UK, and the Greenstar range — combi, system and heat-only — is generally reliable. But no boiler runs forever without attention, and certain faults crop up again and again.

This guide explains what tends to go wrong, what you can sensibly check before paying anyone, where the line is between a homeowner job and a Gas Safe job, and roughly what each repair costs.

If your boiler is showing a specific code, our dedicated guide to Worcester Bosch error codes decodes the common EA, E9 and A1 messages. If the symptom is purely no hot water with the heating still working, the more focused page on Worcester Bosch: no hot water walks through that one in detail. This page is the wider repair picture.

Likely cause	Signs you'll notice	Safe to DIY?
Low pressure / lockout	Gauge below ~1 bar; boiler won't fire.	Yes — top up via the filling loop
Stuck diverter valve	Warm radiators but cold taps (or the reverse).	No — sealed boiler, engineer only
Fan or pressure-sensing fault	Lockout on safety, often an ignition-type code.	No — sealed combustion circuit
PCB (control board) failure	Random lockouts, odd display, no response.	No — engineer only
Ignition fault (EA codes)	Boiler tries to light, fails, locks out.	One reset only — then Gas Safe engineer
No hot water	Faulty flow sensor/thermistor or limescale.	No — engineer only

The most common Worcester Greenstar faults

Low pressure and lockout

The single most frequent call-out isn't really a fault at all. If the pressure gauge drops below about 1 bar, a Greenstar will often lock out and refuse to fire. The fix is usually a homeowner one: top the system back up to roughly 1 to 1.5 bar using the filling loop (see the safe checks below).

If the pressure keeps falling after you top it up, there's a leak somewhere — that does need an engineer.

Stuck diverter valve

On a combi, the diverter valve switches flow between heating and hot water. When it sticks, you get the classic "warm radiators but cold taps" — or occasionally the reverse. The valve sits inside the sealed boiler, so replacing it is engineer work, not a DIY job.

Fan or pressure-sensing fault

The fan drives flue gases out, and an air-pressure switch confirms it's running before the boiler lights. A worn fan, a blocked sensing tube or a failed switch will lock the boiler out on safety and often show an ignition-related code. This is internal, sealed-circuit work.

PCB (control board) failure

The printed circuit board is the boiler's brain. When it fails the symptoms can be erratic — random lockouts, the display behaving oddly, or the boiler simply not responding. A PCB is one of the pricier parts, and on an older boiler it can be the point where replacement starts to make more sense than repair.

Ignition faults (EA codes)

Greenstar models flag ignition problems with codes in the EA family. The boiler tries to light, fails to detect a flame, and locks out. Causes range from a gas-supply issue to a dirty electrode or a faulty gas valve. One reset is reasonable; if it locks out again, it needs diagnosing — this is gas work and never DIY.

No hot water

Beyond the diverter valve, no hot water can come from a faulty flow sensor or thermistor (the boiler can't tell a tap has opened), or from limescale building up in the heat exchanger in hard-water areas. Our no hot water guide covers this thoroughly.

Safe checks you can do before calling anyone

Plenty of "faults" clear with a two-minute check. None of these involve gas, the flue or opening the boiler:

• Check the pressure gauge. Cold, it should read about 1 to 1.5 bar, rising to roughly 2 bar when hot. Below 1 bar, top up slowly using the filling loop — the braided silver hose under the boiler — opening both valves until the gauge reaches around 1.5 bar, then closing them. Your Worcester manual shows the exact loop for your model.
• Bleed the radiators if some are cold at the top while the boiler runs — trapped air is a common cause of patchy heating.
• Check the power and fuse. Confirm the boiler has power and the fused spur or plug hasn't tripped.
• Check the thermostat or programmer. A flat battery in a wireless thermostat, or settings lost after a power cut, can stop the boiler responding.
• Thaw the condensate pipe in cold weather. If the external white plastic pipe has frozen, the boiler may lock out; warm water (not boiling) poured over the frozen section can clear it.
• Try one front-panel reset. Press reset once and wait a minute. Our guide to resetting a Worcester Bosch boiler shows how. If the fault returns immediately, stop and book an engineer — repeated resets won't fix anything.

When to book a Gas Safe registered engineer

If the safe checks above don't restore normal running, the cause is almost certainly internal.

Book a Gas Safe registered engineer for a stuck diverter valve, a fan or pressure-switch fault, a PCB failure, an EA ignition lockout that won't clear, a faulty flow sensor or thermistor, suspected limescale in the heat exchanger, or any leak that keeps dropping your pressure.

You can confirm an engineer's registration at the Gas Safe Register. If you ever smell gas, leave the property and call the National Gas Emergency line on 0800 111 999.

Indicative Worcester repair costs (2026)

There's no single price — it depends on the part, your boiler's age, your area (London and the South East run higher) and whether the fix needs a return visit for a part. The figures below are parts and labour combined, indicative and last checked in June 2026. They're typical ranges, not quotes. Always get the price in writing before work starts.

Repair	Why it fails / what you'll notice	Indicative cost
Pressure top-up only	Low pressure with no leak — often a homeowner job, or a quick visit.	£0–£90
Diverter valve	Warm radiators, cold taps (or vice versa).	£200–£400
Fan	Lockout on safety, often with an ignition-type code.	£200–£450
Flow / pressure sensor	Intermittent lockouts; no fire when a tap opens.	£120–£300
Gas valve	Ignition faults; Gas Safe-only, never DIY.	£250–£500
PCB (control board)	Erratic behaviour or no response; pricey on older units.	£300–£600
Heat exchanger / descale	Weak hot water in hard-water areas; may need a flush.	£300–£600

For the brand-agnostic picture, our wider boiler repair cost guide sets these figures in context, including the call-out fee most independent engineers charge just to attend.

Repair, or let cover handle it?

Several of these Worcester repairs — a PCB, a fan, a heat exchanger — can run into the hundreds once parts and labour are added up.

A boiler cover policy turns that into a fixed monthly cost and a number to call when something goes wrong, which is why many owners of older Greenstar boilers take it out.

Whether it's worth it depends on your boiler's age and your appetite for surprise bills; our guide on whether boiler cover is worth it lays out the trade-offs.

You can also compare boiler cover from our selected panel to see what each plan includes — check the excess and any limescale or pre-existing fault exclusions before you buy.

FAQ

This article is general information, not advice, and reflects a selected panel of providers rather than the whole market. Prices and ranges are indicative for 2026. Always use a Gas Safe registered engineer for gas work.