Worcester Bosch 9A 362 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch 9A 362 fault code mean?
The 9A 362 fault code indicates that the boiler's Heat Control Module (HCM) is not correctly matched to the appliance. The HCM is the electronic control unit responsible for managing the boiler's heating functions — think of it as the brain that coordinates burner operation, temperature control, and system responses. When the boiler detects that the fitted HCM does not correspond to the expected configuration for that model, it raises the 9A 362 fault and locks out to prevent potential misoperation. This is essentially a control-module mismatch error, and because it sits firmly in the PCB and electronics category, it requires a Gas Safe registered engineer to investigate and resolve.
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 HCM installed Common
The most common trigger is that an HCM intended for a different Worcester Bosch model has been fitted — typically following a previous repair where the incorrect replacement part was sourced or installed. The boiler performs an internal compatibility check on start-up and flags the mismatch immediately.
- HCM loose or poorly seated Sometimes
Even if the correct module is present, a loose connection or an HCM that has not been fully and securely seated in its housing can cause the boiler to read it as absent or invalid. Vibration over time can work connectors loose, prompting this fault to appear intermittently.
- Faulty or corrupted HCM Rare
In rarer cases, an HCM that was originally correct and properly fitted can develop an internal fault or firmware corruption, causing the boiler to no longer recognise it as a valid module. This is less common but can occur on older appliances or after a significant power surge.
How to fix it
- Check the boiler display and note the full code DIY safe
Confirm the display is showing 9A 362 rather than a different 9A sub-code. Knowing the exact code helps the engineer identify the fault quickly before they arrive.
- Attempt a boiler reset DIY safe
Press and hold the reset button for approximately two to three seconds. If the boiler restarts and runs normally, monitor it over the next hour. If 9A 362 reappears — or the boiler fails to fire up at all — do not attempt further resets, as repeated resets will not resolve an HCM mismatch and can mask the fault history.
- Check your gas supply is working DIY safe
Confirm other gas appliances in your home (hob, gas fire) are working normally. If there is a wider gas supply issue, contact your gas supplier. However, a gas supply problem would normally produce a different fault code on a Worcester Bosch boiler, so this step is simply a quick sanity check.
- Do not open the boiler casing or touch the HCM Gas Safe engineer
The HCM is an internal electronic component. Removing the boiler casing and attempting to reseat, replace, or inspect the HCM yourself is not legally permitted unless you hold Gas Safe registration. Leave this entirely to a qualified engineer.
- Call a Gas Safe registered engineer to diagnose and replace or reseat the HCM Gas Safe engineer
A Gas Safe engineer will open the boiler, verify whether the fitted HCM is the correct part number for your specific boiler model, reseat any loose connections, or replace the module with the correct compatible unit. You can verify any engineer's Gas Safe credentials at gassaferegister.co.uk before they attend.
Parts you may need
- Heat Control Module (HCM) — model-specific · from £120
- HCM wiring harness / connector loom · from £35
- PCB to HCM interface connector · from £18
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
Is the 9A 362 fault dangerous?
It is not an immediate safety emergency in the way a gas leak or carbon monoxide alert would be, but you should not ignore it. The boiler has locked out because it cannot verify its own control module, which means it will not operate reliably. Stop using the boiler and call a Gas Safe engineer promptly rather than repeatedly resetting it.
Can I just buy a replacement HCM myself and fit it?
No. Sourcing the part yourself is possible in theory, but fitting any component inside a gas boiler requires Gas Safe registration by law in the UK. Beyond the legal requirement, fitting the wrong HCM variant — there are several model-specific versions — would simply reproduce the same fault code. Let an engineer source and fit the correct matched part.
How much does it typically cost to fix a 9A 362 fault?
Most homeowners pay somewhere between £150 and £380 all-in, covering the engineer's callout, labour, and the replacement or reseating of the HCM. If the module only needs reseating rather than replacing, costs sit at the lower end. On older or discontinued models where the HCM must be ordered in, you may face a second visit, which adds labour cost. In exceptional cases involving wider PCB damage, costs can exceed £400, but that is not typical for this specific fault.
Why has this fault appeared after a recent boiler service or repair?
If 9A 362 has appeared shortly after an engineer visited, the most likely explanation is that a replacement HCM was fitted but was not the correct variant for your exact boiler model — or the module was not fully seated before the case was closed. Contact the engineer who carried out the work; they should return to rectify it, ideally at no additional charge if the incorrect part was their error.