Error A8 362

Safety first:

1. If you are unsure about any electrical work, stop and call a qualified electrician or Gas Safe engineer. Do not open sealed parts of the boiler, work on the gas supply, or touch live electrical terminals.

2. Turn off the boiler at the external isolator switch if the boiler is showing repeated faults and leave it off until a professional has inspected it.

3. If you must inspect, switch off the household consumer unit (or the boiler circuit breaker) before removing any covers, and ensure nobody switches the circuit back on while you work.

Initial homeowner checks (safe, non-invasive):

1. Check whether other electrical appliances or lights in the house are dimming, flickering or behaving oddly. If multiple appliances are affected the issue may be a mains supply problem and you should contact your electricity supplier or an electrician.

2. Check the boiler display: note the exact fault code (A8 362) and any accompanying messages or flashing lights. Take a photo or write down the code, date and time — this will help the engineer.

3. Check the house consumer unit for a tripped RCD/MCB and check any isolator switches for the boiler. Reset only if you understand why it tripped; if it trips again, leave it and call an electrician.

4. Make sure the boiler is actually getting mains power: check the boiler isolator switch and any fused spur, and confirm other circuits in the house are live.

5. Try a boiler reset once: on Greenstar i press and hold the reset or OK button for about 8 seconds until the display reboots. If the fault returns immediately or repeatedly, do not keep resetting.

Specific diagnostic steps (only if competent and safe to do so):

1. If you have a qualified electrician available, have them measure the incoming mains voltage at the consumer unit and, if necessary, at the boiler terminals during a call for heat. Normal voltage should be around the nominal supply (e.g. ~230V UK); persistent low readings or large drops under load indicate a supply problem.

2. If mains voltage is correct and stable, the fault points to an internal boiler communication/module issue. With the boiler isolated and only if you are competent, visually inspect the boiler electronics area for obvious signs: loose ribbon or multi-pin connectors, corrosion, burn marks or a dislodged code plug/HCM module. Do not probe live circuits.

3. If connectors look loose, a qualified engineer can reseat the connectors and re-check operation. If the HCM is the wrong type or incorrectly coded (error 9A 362 in some references means incorrect HCM fitted), the HCM or code plug will likely need replacing with the correct part by a Gas Safe engineer.

4. Check for recent work or parts changes: if the boiler was recently serviced or a control module swapped, confirm the correct replacement HCM was used and fitted correctly.

5. If the fault appears intermittent and tied to heavy electrical loads (e.g. washing machine, electric vehicle charger starting), consider having an electrician assess and possibly upgrade or balance the supply.

When to call a professional and next steps:

1. Call a Gas Safe registered engineer if the boiler shows A8 362 and your simple checks (power at isolator, reset attempt) don’t clear it. An engineer will have the correct test tools and Worcester diagnostic knowledge to check the HCM, code plug, connectors and control PCB and to replace parts safely if needed.

2. If an electrician confirms low mains voltage or wiring faults, have those corrected before any boiler parts are replaced. Persistent low voltage must be fixed at source or it can damage the boiler electronics.

3. Provide the engineer with the exact error code (A8 362), photos, the boiler serial number, and any recent service history or work done to help speed diagnosis.

Final notes:

- Do not attempt gas or PCB replacement yourself. HCM or PCB work and mains electrical repairs must be done by qualified engineers.

- If the fault is due to a transient or a one-off spike and a reset clears it, monitor the boiler. Repeated faults mean professional intervention is required.

- If the problem is mains related, contact your electricity supplier or a qualified electrician; if it is HCM/module related, contact a Gas Safe engineer or your Worcester Bosch service support.