Common problems guide

The most common Worcester Bosch 35 RSF problems

The faults most likely to send a Worcester Bosch 35 RSF into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
8 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 6 most common faults

01
A1 High DIY-safe

Your boiler has detected that there is not enough water circulating through the system, which could be caused by a leak or a pump that has stopped working.

What to try first

Check for any visible water leaks around the boiler or radiatorsEnsure the system pressure is topped up to 1.5 bar using the filling loopTry restarting the boiler to see if the pump clears itself

Est. cost
£180-450
Parts
Circulation Pump, Pump Head, Auto Air Vent
Full guide for A1
02
EA High DIY-safe

Your boiler has stopped working because it cannot light the burner, which is usually caused by a problem with the gas supply or the ignition system within the unit.

What to try first

Check if your gas meter has credit and that the main gas lever is turned on.Try to relight other gas appliances, like a hob, to confirm there is a gas supply to the house.Press and hold the reset button for five seconds once gas supply is confirmed.

Est. cost
£120-350
Parts
Ignition Electrode, Gas Valve, Flame Sensing Lead
Full guide for EA
03
A8 High Engineer

Your boiler has lost its connection to the external heating controls, meaning the thermostat and the boiler are no longer talking to each other.

Est. cost
£90-180
Parts
FX RF Receiver, External Temperature Sensor, Control Wiring
Full guide for A8
04
E2 High Engineer

Your boiler's internal thermometer that measures the temperature of the water heading to your radiators has developed a fault and is providing an incorrect reading.

Est. cost
£90-160
Parts
Central Heating Flow NTC Sensor, Sensor Wiring Harness
Full guide for E2
05
235 High Engineer

Your boiler's computer brains are not speaking the same language and need a software update or a component reset to work together correctly.

Est. cost
£120-£350
Parts
Heat Control Module (HCM), Electronic Control Board (PCB)
Full guide for 235
06
360 High Engineer

Your boiler's internal computer chips are not communicating correctly or do not match, preventing the system from starting up.

Est. cost
£180-350
Parts
Heat Control Module (HCM), Printed Circuit Board (PCB)
Full guide for 360
Parts most often replaced

on the Worcester Bosch 35 RSF

Circulation PumpPump HeadAuto Air VentIgnition ElectrodeGas ValveFlame Sensing Lead

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Worcester Bosch shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 8-code list for the Worcester Bosch 35 RSF

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →