Saunier Duval Boiler Repairs

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Saunier Duval Boiler Repairs London

Gas Safe registered engineers • 24/7 call handling • London wide

Call Now: 0203 868 6251

Tell us the fault code and model. We will advise the safest next step.

Common Saunier Duval models we repair include Themaclassic, Themafast, Isofast, and Isotwin, with frequent calls for codes F22, F28, F75, and F29.

We fix Saunier Duval boiler fault codes, no heating, no hot water, lockout, leaking, and low pressure across London.

We also offer boiler servicing and boiler installation across London.

Quick Navigation

• Safety First
• Quick Checks Before You Call
• Fault Code Table
• Most Searched Problems
• Why Saunier Duval Boilers Fail
• Models We Repair
• Repair or Replace

Safety First

Smell gas? Turn off the gas supply at the meter if it is safe to do so. Open windows. Leave the property. Call the National Gas Emergency Service on 0800 111 999. Do not use switches, and do not use naked flames.

CO alarm sounding? Open windows immediately. Leave the property. Call 999. Do not re-enter until cleared by emergency services.

Boiler leaking heavily? Turn off the boiler at the controls. If safe, turn off the water supply. Call an engineer.

Quick Checks Before You Call

Before calling an engineer, these safe checks may resolve simple issues with your Saunier Duval boiler.

Check the gas supply
Is gas working at other appliances in your home? If not, check your meter and any prepayment credit.

Check the pressure gauge
Pressure should read around 1.0 to 1.5 bar when cold. If below 1 bar, you may need to repressurise using the filling loop.

Check the thermostat
Is the room thermostat set above current room temperature? Are the batteries working?

Check the timer or programmer
Is the heating scheduled to be on? Check the clock is set correctly.

Try a single reset
Locate the reset button on your Saunier Duval boiler. Press once and wait. If the fault returns, do not keep resetting. Call an engineer.

Check the condensate pipe
In cold weather, the external condensate pipe can freeze. Look for a white plastic pipe exiting through an outside wall. If frozen, pour warm water over it gently.

Saunier Duval Fault Codes

Note: Many Saunier Duval models use F-codes similar to Vaillant. If your code format looks different, tell us your model when you call.

Common Saunier Duval fault codes and what to do

Most Searched Saunier Duval Problems

If you are seeing a lockout, loss of hot water, or your Saunier Duval boiler keeps resetting, tell us the fault code and model and we will confirm the safest next step.

F28 – ignition failure

F28 is the most common Saunier Duval fault code. The boiler tries to ignite but no flame is detected. Common causes include gas supply issues, a faulty ignition electrode, or a blocked condensate pipe in winter. Check gas is on elsewhere in the home. Try one reset. If the lockout returns, stop and call an engineer.

F22 – low pressure

If your Saunier Duval shows F22, system pressure has dropped below the minimum threshold. Top up via the filling loop to around 1.0 to 1.5 bar when cold. If pressure drops again within days, there may be a leak in the system or a failing expansion vessel. Call an engineer to find the cause.

F75 – pump or pressure sensor fault

F75 indicates the boiler cannot detect a pressure change when the pump starts. This can be caused by a faulty pump, a stuck pump, or a failed pressure sensor. Check the pressure gauge first. If pressure is normal, call an engineer to diagnose whether the pump or sensor needs attention.

No hot water but heating works

On Saunier Duval combi boilers, you may get heating but no hot water, or the reverse. This often points to a diverter valve issue. The diverter valve directs hot water between taps and radiators. When it wears or sticks, hot water delivery becomes unreliable. Call an engineer for diagnosis.

Why Saunier Duval Boilers Develop Faults

Saunier Duval is part of the Vaillant Group, sharing many components and fault codes. Here is what we commonly see.

Ignition electrode wear

Ignition faults (F28, F29) can occur when the ignition electrode wears or becomes coated with carbon. Condensate blockages in winter can also contribute to repeated lockouts.

Pump and pressure sensor issues (F75)

The F75 fault is common on Saunier Duval boilers. It can indicate a seized pump, air in the pump, or a failed pressure sensor. Sometimes the pump just needs freeing off; other times it needs replacing.

Low pressure and expansion vessel faults (F22)

Low pressure faults often point to a failing expansion vessel or a weeping pressure relief valve. The expansion vessel absorbs pressure changes as water heats and cools. If the diaphragm fails or the air charge is lost, pressure drops can occur.

Gas valve faults (F61, F62)

Gas valve faults require immediate attention from an engineer. Do not attempt to reset repeatedly if you see F61 or F62.

Diverter valve on combi boilers

The diverter valve directs hot water between your taps and radiators. When it wears or sticks, you may get heating but no hot water, or the reverse.

Saunier Duval Models We Repair

We repair Saunier Duval combi, system, and regular boilers in London, including:

Themaclassic range: Themaclassic 24, Themaclassic 30
Themafast range: Themafast 24, Themafast 30
Isofast range: Isofast 28, Isofast 35
Isotwin range: Isotwin with integrated cylinder
Other models: Themaplus, Semia, and older Saunier Duval units

Saunier Duval parts are available through the Vaillant Group network. We check availability before attending and advise honestly if repair is not viable or cost effective.

Repair or Replace Your Saunier Duval Boiler?

We help you decide based on age, reliability, and parts availability.

Repair makes sense when

• Boiler is under 10 years old
• This is the first major fault
• Parts are readily available
• Boiler has been regularly serviced

Replacement may be better when

• Boiler is 12 to 15 years old or more
• You have had multiple breakdowns recently
• Parts are obsolete or hard to source
• The boiler is undersized for the property
• Energy bills are higher than expected for the property size

Our engineers give honest assessments. We focus on safety and reliability, not pushing unnecessary replacements.

Saunier Duval Boiler Servicing

Annual servicing reduces breakdown risk and keeps your Saunier Duval boiler running efficiently. See Boiler servicing London.

Landlords and Letting Agents

We provide boiler repairs and gas safety certification for landlords across London. See Landlord gas safety certificate (CP12).

Saunier Duval Repairs Across London

London wide coverage for Saunier Duval boiler repairs. Book an engineer or view our London areas we cover.

Have your postcode and fault code ready and we will confirm the quickest appointment slot.

Other Boiler Brands We Repair

Worcester • Vaillant • Ideal • Baxi • Glow-worm • Viessmann • Potterton • Vokera • Alpha • Ferroli

View all brands

Saunier Duval Boiler Repair FAQs

How quickly can you attend for a Saunier Duval breakdown?

We offer same day attendance where slots are available. For no heating or hot water, we prioritise urgent breakdowns. Call our 24/7 line and we will advise availability.

Do you carry Saunier Duval parts?

We stock common Saunier Duval parts including diverter valves, pumps, pressure sensors, ignition electrodes, and PCBs. Parts are shared with the Vaillant Group range.

Is it safe to reset my Saunier Duval boiler?

Try one reset. If the fault returns after resetting, stop and call an engineer. Do not reset at all for F27, F61, or F62 faults.

How much does a Saunier Duval boiler repair cost?

Costs vary depending on the fault and parts required. We diagnose first and quote before any repair work begins.

Related Services

• Emergency boiler repairs
• Boiler servicing London
• Boiler installation London
• Power flush London
• Landlord gas safety certificate (CP12)
• London areas we cover

Speak to Our Team

For safe next steps, call now.

Call 0203 868 6251 | Book an Engineer

Gas Safe registered • 24/7 call handling • Quote before work