Common problems guide

The most common Saunier Duval Sylva problems

The faults most likely to send a Saunier Duval Sylva 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.
4 documented codes
4 most common
2 DIY-safe checks
2 engineer needed

The 4 most common faults

01
Safety lock-out High DIY-safe

Your boiler has detected trapped air bubbles that are preventing it from running safely, so it has shut down to protect itself.

What to try first

Check your radiator valves and make sure there are no leaksUse a radiator key to bleed any trapped air from your radiators until water flows out steadilyOnce bled, check your boiler pressure gauge and use the filling loop to top it back up to 1.5 barReset the boiler using the button on the control panel

Est. cost
£80-120
Parts
Automatic air vent, System pressure gauge, Filling loop
Full guide for Safety lock-out
02
Loss of water indicating light High DIY-safe

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

What to try first

Locate the filling loop (usually a silver braided hose with one or two valves) underneath the boiler.Slowly open the valve(s) to allow mains water into the system while watching the pressure gauge.Close the valve(s) tightly once the needle reaches 1.5 bar.Restart your boiler.

Est. cost
£0-£120
Parts
Filling loop, Pressure relief valve, Expansion vessel
Full guide for Loss of water indicating light
03
Overheating safety High Engineer

Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent any damage or safety issues.

Est. cost
£120-250
Parts
Limit thermostat, Pump, Diverter valve
Full guide for Overheating safety
04
Air flow rate safety device Emergency Engineer

Your boiler has detected that air cannot flow correctly through the exhaust flue, so it has safely shut itself down to prevent any harmful gases from building up.

Est. cost
£120-250
Parts
Air pressure switch, Flue fan, Venturi tube
Full guide for Air flow rate safety device
Parts most often replaced

on the Saunier Duval Sylva

Automatic air ventSystem pressure gaugeFilling loopPressure relief valveExpansion vesselLimit thermostat

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 Saunier Duval 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 4-code list for the Saunier Duval Sylva

Related guides

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