Vaillant Boiler F65 Fault Code
The Vaillant fault code F65 boiler PCB Overheat Q & A or require an engineer for an emergency boiler repair.
The Vaillant Boiler Fault Code F65 Error Common Q&A
Vaillant Boiler F65 Fault Code
- What does the F65 error code mean on my Vaillant boiler?
- What does the printed circuit board do?
- What causes a PCB unit to overheat, and display a F65 fault code?
- Will a reset provide a temporary fix for the F65 fault code?
- How will I know if mains voltage is the problem causing the F65 error?
- How will an engineer know if connections are loose, or degraded on the PCB?
- If I have an old boiler, will I need to replace the PCB to fix the F65 fault?
- How does water damage cause an F65 fault, and is there a way for me to check for water damage?
- Can a water damaged PCB be fixed, to eliminate the F65 fault code?
- How do I know if a faulty PCB unit is causing the F65 fault code?
What does the F65 error code mean on my Vaillant boiler
According to Vaillant, the F65 fault code will appear when the main PCB (printed circuit board) temperature is too high for it to operate without damage.
What does the printed circuit board do
The PCB, or printed-circuit-board, interacts with all electrical components inside and outside of the boiler.
As an example.
When you demand for heat or water (using the thermostat), the boiler fires out various signals.
It will tell the fan to fire up (to create a draught that expels flue gases). It then communicates with the air pressure sensor to check air pressure is stable.
Once water is heated via the heat exchanger, the PCB will demand the pump to circulate this water around the heating system.
And, electrical resistance from the NTC thermistors monitor the temperature of the flow and return pipes.
This signal is sent back to the boiler to let it know if it needs more gas, so it can signal the gas valve to open. Or, it signals to the PCB that no more fuel is needed, so the gas valve closes.
Any weak signal in the sequence above will result in a fault.
The PCB doesn’t just monitor and interconnect all parts during operation.
It gets feedback from various sensors monitoring temperature, air pressure, boiler water pressure and flue gases.
Essentially, these are all safety alerts. When one is triggered, the boiler locks out and displays a fault code, like the F65 code you are seeing.
What causes a PCB unit to overheat, and display a F65 fault code
The fault-finding mission to fix the F65 on your Vaillant boiler will cover:
- An electrical problem at the mains; there’s an issue with the input voltage
- Loose, degraded or water damaged connections to and from the PCB
- The PCB is faulty and needs replacing
Will a reset provide a temporary fix for the F65 fault code
After resetting a boiler, fault codes will usually disappear, at least for a few minutes. But, the unit will usually pick up on the fact the fault is still present, and lockout again.
It’s not wise to keep resetting your boiler. Depending on the exact part that is damaged, and the level of damage, resetting the boiler could induce further expensive repairs.
The boiler locks out as a precaution to protect you, and its internal components.
How will I know if mains voltage is the problem causing the F65 error
The most common symptom of a mains voltage problem, is multiple appliances failing.
CWhen the voltage is above what’s considered normal, it’s called over voltage.
Some appliances will have more tolerance for this than others (for instance, the appliance might be a non-UK specific product designed to withstand higher voltages).
Essentially, this could be a mains utility issue.
If you have a problem whereby multiple appliance are failing, including your boiler, it’s worth testing the input voltage to your property.
The quickest way to determine whether this is an input voltage or wiring problem, is to speak to an electrician.
They’ll quickly be able to test and determine where the problem lies (and, it means you won’t have weeks for a utility supplier to come out to you).
How will an engineer know if connections are loose, or degraded on the PCB
A visual inspection of the circuit board will quickly highlight any loose or degraded connections.
This is more common on older boilers than newer ones.
For a start, newer boilers tend to have electrical units that are better sealed, and are longer lasting.
Secondly, this is something that happens over time; general wear and tear.
A newer boiler (under 5 years old) with a problem like this is most likely under manufacturer’s warranty, as it shouldn’t happen.
After the initial visual inspection for loose and damaged connections, another visual check can assess the condition of the circuit board itself.
PCBs are incredibly fragile, and the board itself can crack. Any crack that passes through a soldered connection can cause problems.
Soldered joints are the final thing that the engineer will check.
It’s important these connections are solid. If they are not, they’ll be sending intermittent signals to boiler parts, and be receiving the same in return.
If I have an old boiler, will I need to replace the PCB to fix the F65 fault
Old boilers can turn out to be an absolute money pit. If the PCB is malfunctioning, or showing excessive signs of wear, it’s usually best to replace the complete PCB, rather than trying to fix it.
The problem is, PCBs are not usually the first parts on a boiler to malfunction. That means that expensive parts like the gas valve, heat exchanger, pump, fan and even the air pressure sensor could be close behind.
The PCB itself could cost around £400 to replace. With that cost, and the cost of just 2-3 of the above parts being replaced soon, that represents a price that’s closing on having a whole new boiler (including installation).
Get your engineer to inspect not just the PCB, but all other expensive parts too. This will determine whether the more cost effective long-term option, is a new boiler replacement.
How does water damage cause an F65 fault, and is there a way for me to check for water damage
Water damage is a big killer of a boiler’s electrical components.
Usually, they’ll be obvious signs of leaks. So, if you’re finding small pools of water below the boiler casing, or water dripping from the casing, there’s a leak inside
Although newer boilers have sealed electrical units, a visible sign of water around the boiler and the F65 fault being displayed, is signifying that the water may have made its way into the PCB.
Another thing you might have noticed alongside water dripping, is a minor burning smell.
Water dripped directly onto electrical connections can cause a power surge. This surge can lead to burnt out connections, and that is what you’re smelling.
As we’ve mentioned above, unless PCBs have obvious loose connections, the fix is usually a replacement.
Not just because the PCB takes an incredible amount of time to recondition, but there’s no telling if other parts of the circuit board have been partially damaged, and are ready to break too.
The last thing you want is to spend time and money fixing the PCB, only to find it needs to be replaced just months down the line.
How do I know if a faulty PCB unit is causing the F65 fault code
A boiler that acts randomly, is usually a sign of (but, not limited to) a PCB fault.
- Boiler turns on and off randomly, even when there’s no demand from the thermostat
- Temperature gets too hot
- Boiler cycles off before getting radiators up to temperature
- There’s a flickering on the display panel
- The fan or pump cycle off and on at random, causing the boiler to stop heating water
As we mentioned in our explanation of what a PCB is, it provides and receives signals. An interruption of these signals, results in an interruption of operation.
A typical example could be a loose connection to the fan and air pressure switch.
The boiler needs to know the fan is operational before it will fire up. If the connection is weak, or loose, it might not receive that signal.
So, even though the fan is spinning, the boiler PCB doesn’t receive the signal to say it is, and therefore, doesn’t fire up for heat.
Other Vaillant Fault Codes And Error
If your looking for the list of error codes relating to the Vaillant boiler then please read the article Vaillant Boiler Fault Codes And Cures