Vaillant Fault Finding
Diagnosis for recurring lockouts, fault codes, hot water problems, pressure loss and intermittent boiler behaviour.
Fault Finding Boiler Repairs
Vaillant Boiler Repair – Emergency & Fixed Price Service
Expert Vaillant boiler repair from Gas Safe engineers across Berkshire, Surrey, Buckinghamshire & West London. Whether your boiler is not working, not heating water, or showing a fault code, we diagnose the fault and quote before repair work proceeds.
When Your Vaillant Boiler Shows a Fault Code
Vaillant boilers are equipped with a sophisticated self-diagnostic system that displays alphanumeric fault codes on the control panel when it detects a problem. These codes are not simply error messages – they are the boiler's way of communicating precisely which component or system has triggered a safety shutdown or operating limit. Understanding what a fault code means is the first step to getting your heating back on quickly and safely.
It is important to note that fault codes indicate the symptom detected by the boiler's electronics, not always the root cause of the fault. For example, F.75 – a pressure fault – can be caused by a failed pump, a faulty pressure sensor, or a genuine loss of system pressure. Correctly diagnosing the underlying cause requires an engineer with hands-on experience of the Vaillant range, the right diagnostic equipment, and access to the manufacturer's technical documentation.
VaillantCare engineers carry a comprehensive stock of the most commonly required Vaillant replacement parts on their vehicles, meaning that in the majority of fault code call-outs, the repair can be completed on the same visit as the diagnosis – without a second trip to source parts.
Important: Do not repeatedly reset a boiler that keeps locking out on the same fault. Multiple resets without resolving the underlying fault can in rare cases mask a worsening condition and may complicate diagnosis. If your boiler has locked out more than twice on the same fault code, book a repair visit rather than continuing to reset.
Fault Code Reference
Vaillant Fault Code Guide
The six most common fault codes we diagnose and repair. Use our AI assistant for instant code help.
| Code | Fault Name | What It Means | Common Causes | Urgency |
|---|---|---|---|---|
| F.28 | Ignition Failure | The boiler attempted to ignite but did not detect a flame within the allowed time. The boiler locks out as a safety measure. | Faulty ignition electrode, dirty or corroded spark gap, blocked burner, intermittent gas supply | High |
| F.75 | Pump / Pressure Fault | The boiler's pressure sensor did not detect an expected pressure rise when the pump started. Indicates pump failure or sensor failure. | Seized or failed circulating pump, faulty pressure differential sensor, low system pressure | High |
| F.22 | Low Water Pressure | System pressure has dropped below the minimum operating threshold (typically 0.5 bar). The boiler will not fire until pressure is restored. | System leak, failed automatic air vent, pressure relief valve discharge, failed expansion vessel | Medium |
| F.29 | Flame Loss – Urgent | The boiler ignited successfully but the flame was lost during normal operation. This is a potentially serious fault requiring immediate professional attention. | Intermittent gas supply disruption, faulty flame sensor (ionisation electrode), flue terminal blockage, PCB fault | URGENT |
| F.62 | Safety Valve Relay Fault | The boiler's PCB has detected a fault in the safety valve relay circuit. This is an electronics-level fault. | PCB failure, faulty relay, wiring fault, safety valve stuck open or closed | High |
| F.83 | NTC Sensor Fault | The flow and return temperature sensors are not registering the expected temperature differential, suggesting no heat transfer is occurring or a sensor has failed. | Pump failure, frozen condensate pipe (winter), faulty NTC thermistor, low system water volume | High |
Disclaimer: Fault code descriptions are provided for general information only. Actual fault diagnosis requires physical inspection by a qualified Gas Safe engineer. The root cause of a fault code may differ from the listed common causes. VaillantCare accepts no liability for actions taken based solely on the information in this table without professional inspection.
How It Works
Our Repair Process
From your first call to a working boiler – here is what to expect when you book a repair with VaillantCare.
1
Book Your Appointment
Use our online booking wizard or speak to our AI assistant to book a repair visit. We offer same-day emergency slots and next-day standard appointments. You will receive a two-hour arrival window so you can plan your day without waiting in all morning.
2
Diagnosis & Quote
Your engineer will carry out a thorough fault diagnosis using specialist Vaillant diagnostic tools. Once the root cause has been identified, you will receive a clear, written quote for the repair before any work proceeds. There is no obligation to proceed, and the diagnostic fee will be applied against the repair cost if you do.
3
Repair with Genuine Parts
If you accept the quote, the engineer will carry out the repair using only genuine Vaillant replacement parts sourced directly from the manufacturer's supply chain. Most common repairs – pump replacement, ignition electrode, pressure sensor, NTC thermistors – are completed from stock carried on the vehicle on the same visit.
4
Test, Commission & Sign Off
Following the repair, the engineer will carry out a full operational test of the boiler including a combustion analysis, pressure check, and heating cycle test. You will receive a written completion report documenting the fault found, parts fitted, and work carried out. This report is your record for warranty and insurance purposes.
Specialist Repairs
Common Vaillant Faults and Component Repairs
Dedicated repair pages help customers and Google find the right fault pathway instead of relying on one broad repairs page.
Gas Valve Repair
Gas Safe diagnosis for ignition failure, flame loss and suspected Vaillant gas valve faults.
Gas Valve RepairsPCB Faults
Control-board diagnosis for relay faults, sensor issues, intermittent lockouts and electrical control problems.
PCB DiagnosisReady to Book Your Repair?
Same-day and next-day appointments available. Our engineers carry the most common Vaillant parts on their vehicles for first-visit fixes.
Vaillant Boiler Repairs — Frequently Asked Questions
What does Vaillant fault code F.28 mean?
F.28 is an ignition failure fault — the boiler attempted to light but failed to detect a flame. Common causes include a faulty ignition lead, dirty or damaged electrodes, low gas pressure, or a defective gas valve. This fault requires a Gas Safe registered engineer to diagnose and repair safely.
What does Vaillant fault code F.75 mean?
F.75 indicates a pressure sensor or pump fault — the boiler cannot detect a pressure change when the pump starts. This is often caused by a faulty pressure sensor, a blocked or seized pump, or air in the system. An engineer will test both components to identify the root cause.
What does Vaillant fault code F.22 mean?
F.22 is a low water pressure fault. Your boiler pressure has dropped below the minimum operating level (usually 0.5 bar). You may be able to repressurise the system yourself using the filling loop — check our fault codes guide for step-by-step instructions. If pressure keeps dropping, there may be a leak requiring an engineer visit.
Why is my Vaillant boiler not heating water?
If your Vaillant boiler is not heating water, the most common causes are a faulty diverter valve (which directs flow between heating and hot water), a failed pump, a faulty NTC thermistor, or low system pressure. A Vaillant diverter valve repair is one of our most frequent call-outs. An engineer can diagnose the root cause on the same visit and, in most cases, complete the Vaillant PCB repair or component replacement from stock carried on the vehicle.
How much does a Vaillant boiler repair cost in the UK?
Vaillant boiler repair costs in the UK vary depending on the fault and parts required. A diagnostic visit is charged at a fixed call-out rate, which is applied against the repair cost if you proceed. Common repairs — such as pressure sensor replacement, ignition electrode, or pump — are completed from stock on the vehicle. Use our online booking tool to get a fixed-price quote for your area before you commit. Same-day and next-day appointments are available.
Emergency Vaillant Boiler Repairs Across Berkshire, Surrey, Buckinghamshire & West London
VaillantCare engineers attend Vaillant boiler breakdowns in priority towns including Reading, Slough, Windsor, Maidenhead, Bracknell, Wokingham, Uxbridge, Staines, Weybridge and Guildford. We offer same-day attendance for emergency breakdowns where availability allows.
For local service pages, use the VaillantCare service areas hub.
Book an emergency repair online or call us now to speak directly with an engineer.