If your Vaillant boiler suddenly shuts down and flashes the F64 fault code, it’s trying to tell you that something's gone wrong with its internal electronics. Unlike more obvious faults like low pressure or ignition failure, F64 can seem vague – but it points to a sensor or PCB fault that needs proper diagnosis.
I’m Tony from Advanced Heating and Plumbing, and I’ve worked on Vaillant boilers across Watford, Hertfordshire, Middlesex and North London for over 25 years. Here’s what the F64 code actually means – and what you should do next.
Want a fast, professional fix?
If your boiler’s showing F64, it likely needs testing with specialist tools – but don’t worry, I carry everything needed to diagnose it quickly.
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Book a quote or repair onlineWhat Does the Vaillant F64 Fault Code Mean?
The F64 code signals a problem with the boiler’s temperature sensors or its printed circuit board (PCB). These components help the boiler “think” and make safe decisions about when to fire up and how hot it should run.
If one of these sensors becomes faulty, sends false readings, or the PCB has an issue interpreting them, the boiler may shut down to avoid overheating or misfiring.
What Causes F64 in Real Terms?
🔹 Faulty NTC Sensors
NTC (Negative Temperature Coefficient) sensors measure the temperature of water flowing through the boiler. If they fail or produce erratic readings, the PCB can’t manage the heat properly.
🔹 Electrical or PCB Issues
Loose wiring, water ingress, or ageing components on the PCB can cause sensor signals to get scrambled – leading to shutdowns or error codes like F64.
🔹 Damaged or Disconnected Wiring
In some cases, the sensors are fine but the wiring connecting them is damaged. I’ve seen this happen after minor leaks or on boilers that haven’t been serviced in a while.
Can You Fix It Yourself?
Unfortunately, F64 isn’t something you can safely fix without proper tools. However, there are a couple of things you can try before calling out:
- Turn the boiler off and on again at the mains – wait 30 seconds. This will clear any false lockout.
- Check the display – if the error comes back quickly or repeatedly, stop using the boiler.
Don’t attempt to open the casing or test wires yourself – this must be done by a Gas Safe engineer.
Why You Shouldn’t Ignore F64
When it comes to sensor faults or PCB issues, early diagnosis can prevent costly repairs later. A faulty sensor left unchecked could lead to overheating or damage to the heat exchanger.
As a local engineer, I carry testing equipment and genuine Vaillant-compatible parts to diagnose and fix F64 issues without the wait.
Need a Reliable Local Engineer?
I’m Tony – and if you’re in Watford, London, Hertfordshire or Middlesex, I can usually attend the same day. With over two decades working on Vaillant systems, I’ll get to the root of the issue and get your heating back up and running.
✅ Gas Safe registered
✅ Clear pricing upfront
✅ No fuss, no waiting – just expert help when you need it
📞 Call me now on 0800 328 0449
