Worcester Bosch 9A Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch 9A fault code mean?
The 9A fault code — displayed alongside cause code 362 — tells you that the boiler's Heat Control Module (HCM) is either mismatched to the boiler model or cannot be properly detected. The HCM is the brain that manages your boiler's control and configuration, so if the unit fitted does not correspond to the boiler it is installed in, the appliance locks out for safety. The display will show a flashing fault triangle alongside the static cause code 362. Once the underlying issue has been resolved, the boiler must be manually reset to clear the code and resume normal operation.
General guidance only — not a substitute for professional advice. 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
- Wrong replacement HCM fitted Common
The most frequent trigger for a 9A 362 lockout is a Heat Control Module that does not match the specific boiler model it has been installed in. This commonly happens after a service or repair where an engineer inadvertently fits a generic or incorrect variant of the HCM. Even a module that looks physically identical may carry different firmware or configuration settings that make it incompatible.
- Loose or poorly seated HCM connection Sometimes
If the HCM is not firmly seated in its housing or its wiring connector has worked loose — perhaps following a recent repair or due to vibration over time — the boiler's control system may fail to recognise it at all. This can produce the same 9A 362 lockout as a completely mismatched module.
- Missing, displaced, or damaged coding card Sometimes
Worcester Bosch boilers use an internal configuration (coding) card to tell the control system exactly which model variant it is running on. If this card is absent, incorrectly inserted, or has become damaged, the HCM cannot confirm it is matched to the right boiler, triggering the 9A fault.
How to fix it
- Check the boiler display and note the full code shown DIY safe
Confirm the display is showing 9A alongside cause code 362. Take a photo if helpful. This rules out any superficially similar codes and gives your engineer the precise information they need when you call.
- Attempt a single boiler reset DIY safe
Press and hold the reset button for approximately two seconds as described in your user manual. If the boiler fires up and runs normally, monitor it closely over the next few hours. If the 9A 362 code returns, do not keep resetting — repeated resets without fixing the root cause will not resolve a hardware mismatch and may mask the fault.
- Do not remove the boiler casing or touch internal components Gas Safe engineer
Opening the boiler casing and handling the HCM, coding card, or any internal wiring is work that must be carried out by a Gas Safe registered engineer. Doing so yourself is unsafe and, for gas appliances, is contrary to UK gas safety regulations.
- Book a Gas Safe registered engineer to inspect the HCM and coding card Gas Safe engineer
An engineer will open the casing safely, verify whether the fitted HCM carries the correct part number for your boiler model, check that the coding card is present and undamaged, and reseat or replace whichever component is at fault. If a replacement HCM is required, they will source the correct compatible unit and commission the boiler once it is fitted.
Parts you may need
- Heat Control Module (HCM) — Worcester Bosch compatible · from £180
- Boiler coding / configuration card · from £25
- HCM wiring harness / connector · 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 £150–£380, depending on the underlying cause.
Frequently asked questions
What is the 9A 362 code on a Worcester Bosch boiler?
The 9A fault is the main error category, and 362 is the specific cause code that pinpoints the problem as an incorrect or unrecognised Heat Control Module (HCM). Together they tell you — and your engineer — that the control module fitted inside the boiler does not match the model it is installed in, or cannot be detected at all. The boiler locks out until the correct module is confirmed and the code is reset.
Can I fix the Worcester Bosch 9A fault code myself?
The only action a homeowner should take is a single reset attempt. If the fault clears and does not return, great — keep an eye on it. If it comes back, the fix involves opening the boiler casing to inspect or replace the HCM and coding card, which must be done by a Gas Safe registered engineer. Attempting internal boiler repairs yourself is unsafe and not permitted under UK gas safety regulations.
How much does it cost to fix a Worcester Bosch 9A fault?
Most homeowners pay somewhere between £150 and £380 in total (parts and labour combined) to resolve a 9A 362 fault. A straightforward reseating of a loose HCM or coding card will sit at the lower end; sourcing and fitting a brand-new compatible HCM — particularly on an older or less common model — can push costs toward the higher end. Labour rates also vary by region, with London and the South East typically being more expensive. In rare cases where associated PCB damage is found, costs can be higher still — your engineer will advise.
My boiler is over 10 years old and showing a 9A fault — is it worth repairing?
It depends on the overall condition of the boiler and its repair history. If the appliance has been reliable and the only issue is a mismatched HCM, a repair is often worthwhile. However, if the boiler has had several faults recently, is outside its manufacturer warranty, and repair quotes are approaching or exceeding £500, it is worth getting a new boiler quote to compare — a modern A-rated condensing boiler will also reduce your energy bills compared with an older unit.