A straight-talking guide to the faults Worcester Greenstar boilers develop most often, the checks you can safely do yourself, the jobs that need a Gas Safe registered engineer, and what repairs typically cost in 2026.
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.
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.
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.
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.
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.
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.
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.
The golden rule: anything involving the gas valve, gas pipework, the flue, the sealed combustion circuit, the pressure relief valve or removing the boiler casing must only be touched by a Gas Safe registered engineer. There is no safe DIY version of those jobs.
Plenty of "faults" clear with a two-minute check. None of these involve gas, the flue or opening the boiler:
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.
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.
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.
See what a cover plan would include, from a selected panel of UK providers.
Compare boiler coverWorcester parts are generally well-supplied and not unusually costly, so most repairs sit within the typical UK ranges above. The expensive jobs are the same as for any brand — a PCB, a heat exchanger or multiple parts failing at once — which on an older boiler can tip the balance towards replacement.
Only the homeowner-safe checks: topping up pressure, bleeding radiators, checking power and the thermostat, thawing a frozen condensate pipe, and one front-panel reset. Anything inside the sealed boiler — the diverter valve, fan, gas valve, PCB or heat exchanger — is gas work for a Gas Safe registered engineer.
EA codes relate to ignition — the boiler tried to light and didn't detect a flame, then locked out. Try one reset; if it locks out again, book a Gas Safe registered engineer. Our Worcester error codes guide covers it in more detail.
Once a year by a Gas Safe registered engineer. An annual service helps catch wear before it becomes a breakdown and is usually a condition of keeping your Worcester warranty valid.
Most cover providers include the major brands, Worcester among them, though some apply an age limit or exclude pre-existing faults. Check the policy wording and compare boiler cover from our panel to see the terms that apply to your boiler.
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.