Common problems guide

The most common Vokera Syntesi 25E / 29E problems

The faults most likely to send a Vokera Syntesi 25E / 29E 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.
11 documented codes
6 most common
1 DIY-safe checks
5 engineer needed

The 6 most common faults

01
04 High DIY-safe

Your boiler has stopped working because the water pressure inside the system has dropped too low.

What to try first

Locate the external filling loop, usually a silver braided hose under the boiler.Open the small valve(s) at either end to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Ensure both valves are fully closed tightly and reset the boiler.

Est. cost
£80-150
Parts
Filling loop, Pressure relief valve, Expansion vessel
Full guide for 04
02
02 High Engineer

Your boiler is failing to circulate water properly because it cannot sense the flow it needs to heat your home.

Est. cost
£120-250
Parts
Circulating pump, Flow sensor, Isolation valves
Full guide for 02
03
06 High Engineer

Your boiler is struggling to detect the temperature of your hot water, which likely means you will have no hot water available until it is fixed.

Est. cost
£120-200
Parts
DHW NTC thermistor
Full guide for 06
04
07 High Engineer

Your boiler has stopped working because it is unable to accurately measure the temperature of the water inside the unit.

Est. cost
£120-180
Parts
NTC Temperature Sensor
Full guide for 07
05
08 High Engineer

Your boiler has detected that it is running too hot and has automatically shut down to prevent damage to its internal components.

Est. cost
£120-250
Parts
NTC thermistor, Primary heat exchanger, Pump
Full guide for 08
06
09 High Engineer

Your boiler's internal computer is malfunctioning and cannot correctly process its own instructions, which prevents it from operating safely.

Est. cost
£250-400
Parts
Main Control PCB, Wiring harness
Full guide for 09
Parts most often replaced

on the Vokera Syntesi 25E / 29E

Filling loopPressure relief valveExpansion vesselCirculating pumpFlow sensorIsolation valves

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 Vokera 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 11-code list for the Vokera Syntesi 25E / 29E

Related guides

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