The Worcester Greenstar is a mains gas combi / regular boiler. Below are the faults it most often develops, what the error codes mean, and how to get it fixed at a fixed price by a Gas Safe registered engineer.
Variants covered: ZWBR 7-30 HE Plus, ZB 7-28 HE, ZWBR 11-35 HE Plus, ZWB 7-25 HE Combi, ZWB 7-30 HE Combi, 12 Ri, 24 Ri, 30 Si, 25 Si, 24i junior, 28i junior, 12i System, 24i System, 18Ri, 15Ri, 42 CDi, 37 CDi, FS 42 CDi Regular, FS 30 CDi Regular, 15 i System, 18 i System, 36LXi, 30 LXi System, 38CDi Combi…
Hot taps run cold while heating still works — commonly the diverter valve, the flow sensor or the plate heat exchanger scaling up.
The gauge drops below ~1 bar and the boiler cuts out — usually a small leak, a tired expansion vessel or a weeping pressure-relief valve.
It tries to light, fails and locks out — often the spark electrode, gas valve or a flame-sensing fault.
Drips or staining under the case — a seal, the pump, the heat exchanger or a corroded pipe.
Rumbling on the heat exchanger, usually limescale or sludge restricting flow.
Cool rads or slow warm-up — often the pump, a sticking motorised valve or air in the system.
These are the likely causes — a Gas Safe registered engineer confirms the fault on site before any work. If you can smell gas, stop and ring 0800 111 999.
If there's a code on the display, tap it for the meaning, the free checks to try first and a fixed repair price:
One fixed price, no callout fee, a vetted Gas Safe engineer who covers your postcode.