Worcester Bosch F0 258 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch F0 258 fault code mean?
The F0 258 fault code on a Worcester Bosch boiler has two parts that together pinpoint the problem. The F0 prefix signals an internal component failure — when you see it on the display, usually accompanied by a flashing fault LED or flashing reset button, the boiler has detected a serious electronics-level issue. The sub-code 258 narrows this down specifically to the Heat Control Module (HCM) or its control box. The HCM is responsible for regulating temperature and coordinating the boiler's key operating functions, so when it fails or loses a reliable connection, the boiler will typically lock out and stop providing heating and hot water. In short: your boiler's brain (or its link to it) has developed a fault that requires professional investigation.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or failed Heat Control Module (HCM) Common
The HCM itself has malfunctioned or burned out internally. This is the most direct cause of the 258 sub-code and typically results in a hard lockout. The module may have failed gradually through wear or suddenly due to an electrical event.
- Loose or corroded wiring connections to the HCM Common
Even if the HCM is physically intact, a poor electrical connection — due to a loose plug, corroded terminal, or damaged wire — can cause the boiler's diagnostics to flag the module as defective. This is often a quicker and cheaper fix than full component replacement.
- PCB damage or instability Sometimes
The main printed circuit board (PCB) communicates with the HCM; if the PCB has suffered damage or become unstable — for example following a power surge — it may incorrectly report or genuinely trigger an F0 258 fault. The two components are closely linked in the control chain.
- Power surge or transient electrical fault Sometimes
A sudden spike or dip in your home's electrical supply can upset sensitive boiler electronics. If the fault appeared after a power cut, surge, or stormy weather, this is worth mentioning to your engineer as it may point to transient damage rather than gradual wear.
How to fix it
- Check your home's gas and power supply are functioning normally DIY safe
Before anything else, confirm that other gas appliances in your home are working and that your electricity supply is stable. If there has been a recent power cut or surge, note this down — it is useful information for the engineer.
- Attempt a single boiler reset DIY safe
Press and hold the reset button on your Worcester Bosch boiler as described in your user manual (typically for around 3 seconds until the display changes). If the boiler restarts and runs normally, monitor it closely. If the F0 258 fault returns, do not keep resetting — repeated resets will not fix an internal electronics fault and may complicate the diagnosis.
- Do not attempt to open the boiler casing or inspect internal components yourself Gas Safe engineer
Accessing the HCM, control box, wiring, or PCB requires removing the boiler casing and working with internal electrical components. This is not safe or legal for an unqualified person in the UK. Leave all internal inspection to a Gas Safe registered engineer.
- Call a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
A qualified engineer will open the boiler safely, inspect the HCM connections for looseness or corrosion, test the HCM and PCB for correct operation, verify that the installed HCM matches the boiler's specification, and replace any defective components. Always check the engineer is listed on the Gas Safe Register at gassaferegister.co.uk before booking.
Parts you may need
- Heat Control Module (HCM) · from £180
- Main PCB (printed circuit board) · from £220
- HCM wiring harness / connector set · from £35
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£400, depending on the underlying cause.
Frequently asked questions
Can I fix Worcester Bosch F0 258 myself?
No. While you can safely attempt a single reset, the underlying fault — a defective HCM, loose internal wiring, or PCB issue — requires a Gas Safe registered engineer to diagnose and repair. Opening the boiler casing and working on internal components without the correct qualifications is both dangerous and illegal in the UK.
How much does it cost to fix an F0 258 fault in the UK?
If the issue turns out to be nothing more than a loose or corroded connection, the repair cost may be little more than the engineer's callout fee, typically £60–£100 during standard hours. If the HCM or PCB needs replacing, expect to pay in the region of £250–£400 including parts and labour. In rare cases where extensive control system work is needed, costs can rise higher — if your boiler is over 10–12 years old and repair quotes are approaching £500 or more, it is worth getting a new boiler quote for comparison.
What is the difference between the F0 prefix and the 258 sub-code?
Worcester Bosch uses a two-part coding system on many of its boilers. The prefix — F0 in this case — tells you the category of fault (here, an internal component failure, often electronics-related). The three-digit sub-code, 258, identifies the specific component involved, which is the Heat Control Module (HCM) and its control box connections. When you see the full code F0 258 on your display, both parts together are telling you the HCM is the source of the problem.
My boiler is showing F0 258 — will I be without heating and hot water?
Almost certainly yes, at least until the fault is resolved. An F0 fault typically causes the boiler to lock out as a safety measure, meaning it will not fire until the fault is cleared by a professional. In cold weather, contact a Gas Safe engineer as soon as possible. If the boiler is under warranty or you have boiler cover, contact your provider first as they may offer a faster or lower-cost callout.