Vaillant Boiler Repairs London

Vaillant Boiler Repair Help Centre

Common Vaillant faults, fault codes, safe checks, and when to call a Gas Safe engineer.

We specialise in Vaillant boiler repairs across London.

Gas Safe registered engineers for safe diagnosis, repair and testing.

24/7 availability with London wide call handling and booking.

Jump to: Fault Codes · F28 Fault · F75 Fault · Pressure · Frozen Condensate · Repair or Replace

Quick Checks Before You Call Anyone

These take 60 seconds and solve a surprising number of lockouts:

1. Check the pressure gauge: If below 1 bar, top up (see guide below). More detail in our complete pressure guide.
2. Note the fault code: Vaillant displays show F codes like F28, F75, F22. Write it down before calling.
3. Check your fuse box: Boilers need electricity; a tripped switch is an easy fix.
4. Check thermostat and timer: Settings can change after clock changes or dead batteries.
5. Freezing weather? The condensate pipe may be frozen (see winter section below).
6. Reset once only: Press reset once, wait 60 seconds. If it locks out again, stop and call an engineer.

Vaillant Fault Codes

Note: Vaillant fault codes vary by model. If unsure, call us with your model and code and we will advise the safest next step.

F28: Ignition Failure

What is happening: The boiler is trying to ignite but cannot establish a flame after multiple attempts.

Common causes: Frozen condensate pipe (winter), gas supply interruption, faulty ignition components, blocked or damaged flue, gas valve fault.

What to try: Check if your gas hob or other gas appliances work. In freezing weather, check the condensate pipe for ice. If gas supply is fine but the boiler will not ignite, call an engineer.

F75: Pump or Pressure Sensor Fault

What is happening: The boiler cannot detect a pressure change when the pump runs. This is a common Vaillant fault and often needs proper diagnosis.

Common causes: Pump performance issues, pressure sensor faults, air or debris in the hydraulic block, or restricted circulation from system sludge.

What to try: Check the pressure gauge first. If pressure is below 1 bar, top up and reset. If pressure is fine but F75 persists, call an engineer.

F22: Low Water Pressure

What is happening: System pressure has dropped below the minimum operating level.

Common causes: Small leak in system, recently bled radiators, pressure relief valve discharge, expansion vessel needs recharging.

What to try: Top up pressure using the filling loop. If pressure drops again within days, there may be a leak. Read our pressure guide for step by step instructions.

How to Top Up Pressure (Vaillant)

If you are not comfortable using the filling loop, stop and call a Gas Safe engineer.

Do not remove the boiler casing. If you cannot locate the filling loop easily, call an engineer.

1. Locate the filling loop (usually underneath the boiler, a braided silver hose with one or two valves).
2. Ensure the boiler is off and cool.
3. Open the valves slowly, a quarter turn at a time.
4. Watch the pressure gauge rise to between 1.0 and 1.5 bar.
5. Close both valves fully.
6. Switch the boiler back on.

Do not exceed 2.0 bar. If you overfill, stop and call an engineer.

If you need to top up frequently (more than once a month), there is likely a leak. Call us for a diagnosis.

Frozen Condensate Pipe (Winter)

In freezing weather, a frozen condensate pipe is one of the most common causes behind F28 and F29 lockouts on Vaillant boilers. This is often safe to resolve with the steps below. If you are unsure, or the boiler will not restart, call an engineer.

Signs: Boiler locked out with F28 or F29, freezing temperatures outside, gurgling sound when boiler tries to start.

What to do:

1. Locate the condensate pipe (white or grey plastic pipe exiting to an outside drain).
2. Pour warm water (not boiling) over the frozen section.
3. Reset the boiler once thawed.

Full instructions: Frozen condensate pipe guide.

Why These Faults Are Common in London Homes

• F75 faults: London systems often have sludge and debris that can restrict circulation and contribute to pump and sensor issues.
• Frozen condensate pipes: External pipes exposed to freezing temperatures can cause ignition lockouts.
• Pressure fluctuations: Older London properties can see more frequent pressure drops, especially after radiator bleeding.

Vaillant Models We Repair

• ecoTEC: combi and system range
• ecoFIT: compact combi models
• Older Vaillant boilers: common across London properties

Repair or Replace?

Vaillant boilers typically last 10 to 15 years with proper maintenance. If yours is approaching that age and needs a major repair (PCB, fan, heat exchanger), replacement may be more cost effective.

We give honest advice either way. Read more: Repair or replace? An engineer’s guide.

If you decide on a new boiler: New boiler installation.

Vaillant Servicing

Annual servicing keeps your Vaillant running efficiently and helps maintain warranty terms. Book your boiler service.

Renting? Landlords: Check This

Landlords: Stay compliant with our Gas Safety Certificate (CP12) service. See our full London landlord checklist.

London Wide Coverage

We repair Vaillant boilers across all London boroughs. For coverage and service areas, see our London coverage page.

We Also Repair These Brands

Related Services and Guides