What F0 263 means on a Worcester boiler
F0 263 means the boiler's own electronics have found a problem with themselves, rather than with the gas, the water or the flue. F0 is the display code and 263 is the cause code that narrows it down. The boiler locks out and stays off until someone resets it.
Worcester's installation, commissioning and servicing instructions for the Greenstar 27i and 30i System Compact (document 6 720 807 726) place 263 inside the F0 "Internal error" group of locking faults. The instructions for the Greenstar 9i to 24i System ErP (document 6 720 806 945) describe cause code 263 as "Control box or the HCM is defective." The control box is Worcester's name for the main circuit board (PCB) and its housing. The HCM is the heat control module, which Worcester's own fault tables also refer to as the code plug.
Copies of these manual tables online do not always keep their columns lined up. In the System ErP table, 263 is listed alongside the F0 rows, and Worcester's Greenstar 8000 Life instructions list a code 263 next to the wording "System fault boiler electronics / basic controller". Both readings point the same way: the electronics, not the plumbing.
Which Worcester boilers use F0 263
| Model range | Worcester document | How 263 is described |
|---|---|---|
| Greenstar 27i and 30i System Compact | 6 720 807 726 (2013) | Within the F0 "Internal error" locking faults |
| Greenstar 9i, 12i, 15i, 18i, 21i and 24i System ErP | 6 720 806 945 (2015) | "Control box or the HCM is defective." |
| Greenstar 8000 Life combi | 6720883865 (2021) | Listed alongside "System fault boiler electronics / basic controller" |
Other Greenstar ranges can show different codes for an electronics fault, so write down the full code and the model name printed on the boiler before you look anything up. Our Worcester Bosch fault code hub lists the other codes we cover.
What usually causes F0 263
The cause list for this code is short, and both items sit inside the casing.
A defective control box
The control box runs every part of the boiler, from the fan to the gas valve. If F0 263 keeps returning once the HCM has been checked, this is the part an engineer will look to replace.
A faulty or poorly seated HCM
The HCM plugs into the control box. The actions printed in that section of the System ErP table include checking that the HCM is inserted properly and replacing the control box if necessary, with a referral to Worcester's technical helpline if the fault persists.
Why the power supply is a separate question
Worcester gives mains supply problems their own cause codes. The System ErP table lists 356 for low mains voltage and 328 for an internal error where the mains voltage or frequency may be inconsistent. So 263 points at the electronic parts themselves, although an engineer will still check the supply while diagnosing it.
A one-off lockout or a failing part?
How the code behaves after a reset tells you a lot.
| What you see | What it suggests | Next step |
|---|---|---|
| F0 263 once, after a power cut or storm, cleared by one reset | A single lockout with no sign yet of a failed part | Note the date and keep an eye on it |
| Returns within hours or days | Control box or HCM fault more likely | Book a Gas Safe registered engineer |
| Will not clear at all, or the display behaves oddly | Electronics not completing their start-up checks | Stop resetting and book an engineer |
Safe checks before you call anyone
- Check the power. Make sure the fused spur that feeds the boiler is switched on. If other things in the house have gone off as well, check your consumer unit.
- Think about what happened first. A power cut, a thunderstorm, electrical work in the house or the spur being switched off and on are all worth writing down.
- Reset the boiler. On the Greenstar i System models, the Compact manual explains that a locking fault flashes a warning triangle with the code and needs the reset button on the fascia pressing. Try two or three times at most. Our Worcester boiler reset guide shows where the button is on different ranges.
- Ask for heat after the reset. Turn the thermostat up or switch the programmer on so the boiler has a reason to fire, then watch whether the code returns.
- Look under the boiler. Without removing anything, check for drips or water staining, as water near the electronics is worth mentioning when you book.
Do not remove the casing, unplug the HCM or touch the control box. There is mains voltage inside the boiler, and the control box also manages the gas valve. If you smell gas at any point, leave the boiler off and call the National Gas Emergency Service on 0800 111 999.
What a Gas Safe engineer will do
The engineer will read the fault and cause code, check the HCM is seated correctly and inspect the connections at the control box. They will usually check the mains supply too, so they can rule out the separate supply codes. If the HCM is sound, the likely repair is a replacement control box. Worcester's 8000 Life table gives similar advice for its electronics faults: restart the appliance, check the wiring and code plug, then replace the control unit if the fault persists.
When you book, give the engineer:
- the full code, F0 263, and any other codes you have seen
- the exact model, for example Greenstar 30i System Compact
- how many resets you tried and whether any of them worked
- any power cut, storm or electrical work just before the fault
Typical repair costs in the UK
A fault that clears with one reset and never returns costs nothing. If a part is needed, these ranges are typical and vary by region and model.
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £60 to £150 |
| Reseating or replacing a small part such as the HCM, or repairing a connection | Typically £100 to £180 |
| Control box (PCB) replacement, fitted | Typically £250 to £550 |
A new control box is the expensive end of this fault. Our boiler PCB replacement cost guide covers what affects the price and when an older boiler may not be worth the spend. If your Greenstar shows a different code after the repair, such as Worcester U9, look that code up separately rather than assuming it is the same fault.