Vaillant Boiler F88 Fault Code
The Vaillant fault code F88 boiler lock out gas valve fault problem Q & A, this is normal related to an electrical issue and if you require an engineer for an emergency boiler repair, feel free to use our service.
The Vaillant Boiler Fault Code F88 Error Common Q&A
Vaillant Boiler F88 Fault Code
- What does the F88 fault code mean on my Vaillant boiler?
- What causes the F88 fault code to occur?
- What does the gas valve do, and how does it work?
- What happens when there is a fault with the gas valve?
- Why does my Vaillant boiler lockout and show the F88 fault code?
- Can I fix the F88 fault on a DIY basis?
- How does wiring become loose or damaged, and can it be repaired?
- What if the fault lies with the gas valve?
- How much does a new gas valve cost, and how long will it take to fit?
- If the gas valve has been incorrectly adjusted, will it need to be replaced?
- What else can cause the F88 fault code to be displayed?
- What can cause PCB faults, and what are the signs?
What does the F88 fault code mean on my Vaillant boiler?
According to Vaillant, if your boiler locks out and displays a F88 fault code, the fault lies with the gas valve. And, it’s most likely that the fault is electrical.
What causes the F88 fault code to occur?
There are a few things a gas engineer needs to check to determine the root cause of the F88 fault, including:
- Loose and damaged connections between the gas valve and the PCB (printed circuit board)
- A defective gas valve (replacement needed)
- Incorrect gas valve adjustment
What does the gas valve do, and how does it work?
The gas valve controls the flow of fuel to the burner. The supply of gas varies depending on the boiler’s heat requirements.
But, like all electrical components in a boiler, it’s controlled by the PCB. The PCB gets a signal from the thermostat to heat water. And the temperature of the water is monitored by NTC thermistors.
When they detect that target temperature has been reached, they’ll send a signal to the PCB. In turn, the PCB will tell the gas valve to close.
What happens when there is a fault with the gas valve?
The faults that originate from gas valves and their electrical connections make a boiler operate intermittently.
The gas valve could:
- Not be open, even though it’s signalling to the PCB that it is (it’s stuck)
- Not fully close, or not close at all, and provide too much gas
- Fail to open or close when it’s instructed to do so by the PCB
- Give intermittent signals to the PCB about when it’s opening and closing
This might lead to a range of things such as:
- Immediate boiler lock outs
- Temperature of hot water and radiators too hot or too cold
Why does my Vaillant boiler lockout and show the F88 fault code?
Boilers of all kinds lock out as a safety mechanism. It’s particularly important that they do this when the fault relates to gas.
The lockout helps to protect internal boiler components. For instance, excess gas causing explosive ignition and damage to the burner.
Mostly though, the lock out mechanism is designed to protect you and your family. Too much gas will smother the flame, and that means a dangerous gas leak.
When a flame isn’t detected for what ever reason, the boiler will lock out and shut down the gas valve. The supply of gas is then cut off.
Can I fix the F88 fault on a DIY basis?
A boiler is a gas appliance, and this fault relates directly to gas.
For safety reasons, you shouldn’t work on your Vaillant boiler unless you are Gas Safe accredited.
How does wiring become loose or damaged, and can it be repaired?
If you’re lucky, you’ll have a simple case of loose wiring.
Lots of internal boiler parts vibrate. A typical example would be the heating pump.
Over years, these vibrations can contribute to loosening wires and connections. When wires and connections are loose, they’ll provide the intermittent signals we talked about above.
A simple visual inspection will highlight loose wires and connections, and these can be secured to fix the problem.
But, the gas engineer will need to inspect the condition of wiring, and test using a multi meter.
Any wiring showing obvious damage, or wiring giving off the incorrect electrical readings, needs to be replaced.
What if the fault lies with the gas valve?
After confirming all wires and connections are in working order (and fixing any that aren’t), the fault-finding mission continues to the gas valve.
Like the wiring, this can be tested with a multi meter. This will confirm whether it’s giving and receiving the correct signals.
The engineer will also need to check that the valve isn’t getting partially stuck open, or closed.
On some occasions, the gas valve can be freed. But, if it’s getting stuck due to an electrical fault rather than just a mechanical seizure, it’s likely it will need to be replaced.
How much does a new gas valve cost, and how long will it take to fit?
And, this is why a diagnosis from a professional is important; replacement gas valves are expensive. Misdiagnosing a faulty gas valve can be an expensive mistake.
Expect to pay around £300 for a gas valve replacement. That will cover parts and labour.
You should expect the job to take less than a day.
If the gas valve has been incorrectly adjusted, will it need to be replaced?
Although testing the gas valve will indicate whether it’s been adjusted correctly, the variation of fault codes will help with the diagnostic.
Some newer boilers will display more than one fault code.
In this case it’s likely that the F88 fault code would be coupled with one of the error codes below:
These codes relate directly to gas valve adjustment issues.
When the problem is limited to the adjustment of the gas valve, it’s rare that a replacement is needed.
What else can cause the F88 fault code to be displayed?
According to Vaillant, the most likely culprit is the gas valve, its adjustment, or faulty wiring.
But, that wiring connects the gas valve directly with the PCB, so that shouldn’t be ruled out as a boiler component that’s causing issues.
When older boilers break, it’s typical that the most important and used parts break first. The circuit board on a boiler tells all electrical parts when to operate, and when to stop operating.
So, when electrical faults occur, there’s a good chance they originate from the PCB.
Before replacing the gas valve (which could cost £300 or more), it’s important to check the PCB. If the PCB is also damaged and needs replacing, the total repair bill could be more than £700.
It’s rarely worth spending that kind of money on an old boiler. Instead, a replacement with 5+ years warranty is a much more cost-effective use of your cash.
What can cause PCB faults, and what are the signs?
Apart from old age and overvoltage, water damage is the most common killer of electrical parts in boilers.
So, if you’ve noticed water dripping or pooling below your boiler, it’s worth inspecting every electrical component.
A boiler that’s leaking water isn’t necessarily dangerous. But, that changes when that water meets electrical components.
And, it’s when this water settles on electrical components that it causes connections to burn out, and electrical parts to fail.
When this happens, you’ll start to notice a burning smell coming from your boiler. When the engineer opens the boiler, there will be burnt out connections on the circuit board.
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