Worcester Bosch Fault Code H02 — Diagnose and Fix
Fault code H02 on a Worcester Bosch boiler indicates diverter valve. Diverter valve stuck — replace cartridge (£60–120). Here is the diagnostic order UK Gas Safe engineers follow.
Step-by-step method
1. Confirm the H02 lockout
Power off at the fused spur for 60 seconds, restore and reset. If H02 returns within 5 minutes, proceed. Intermittent H02 points to a sensor or connection, not the PCB.
2. Check pressure, condensate, gas
System pressure 1.0–1.5 bar, condensate unfrozen, gas proven at another appliance — accounts for ~60% of lockouts.
3. Test what H02 points at
Diverter valve stuck — replace cartridge (£60–120).
4. Reset and prove
Reinstate covers (interlocks matter), reset and observe full ignition. Flame current 1–8 µA DC.
5. Gas Safe callout
Gas-side work on a Worcester Bosch requires Gas Safe. Provide the fault code, GC number and serial so parts are pre-ordered.
Frequently asked questions
Reset Worcester Bosch H02 myself?+
Hold reset 5 seconds. If it returns, fault is still present.
Repair cost?+
£120–£280 typical; PCBs £180–£320; sensors £60–£100.
Warranty cover?+
Yes if within warranty and annual services logged.