Vaillant F62 Fault Code - How to fix?

What does the Vaillant F62 Fault Code mean?

The F62 Fault Code, aka F62 Error of the Vaillant and the Vaillant Eco-Tec, means the boiler has detected a flow of gas when the boiler should be off, in other words, the gas valve hasn’t closed.

Vaillant describes the F62 fault code as:
F.62 Gas valve shut off delay Gas valve leaking, electronics defective

The F62 Error: shut your boiler off immediately

You should never attempt to repair the F62 fault code.

If you see the F62 fault code you must shut your boiler off immediately and call your local gas safe registered boiler repair engineer.

If your Vaillant gas valve has failed to close fully a small amount of gas could be passing into the combustion chamber, when the boiler receives a demand for heat and starts the ignition sequence this could result in explosive ignition.

Fluctuations of the water pressure on a boiler

You shouldn’t spend too much time worrying about the pressure in your boiler, the pressure of your Vaillant boiler will fluctuate each time you use it. When you have your heating on the boiler pressure will increase as the system temperature increases and, as the system cools the pressure will naturally reduce.

Expect the fluctuations to be between 1 bar from cold up to about 2 bar when hot with the heating running for an hour or so, readings outside of these parameters ie below 1 bar or above 2 bar, are not uncommon but they might point to a potential fault developing and you should book an annual boiler service with a Gas Safe registered heating engineer to prevent a possible boiler breakdown.

Vaillant F62 Error Code: Common Causes

The main component failures that cause the Vaillant F62 fault will usually be the gas valve, PCB, and electrodes, in some instances it could be caused intermittently by a poor Earth connection either in your Vaillant boiler or household electrics.

What is a boiler gas valve?

The gas valve is the part in the boiler which regulates the flow of gas to the main burner. When the boiler receives a demand for heat from either a tap being opened or a thermostat calling for heat the PCB in the Vaillant boiler will send a signal to the gas valve telling it to open, allowing gas to flow to the main burner.

At the same time as telling the gas valve to open the PCB will also instruct the electrodes to produce a spark in order to ignite the gas, this spark will continue for a short while and pass through the flame generating an ionised current which the PCB will recognise as the burner being open and everything is as it should be.

When the demand for heat has been satisfied the Vaillant boiler will then tell the gas valve to shut, if the sensors detect any flow of gas after this instruction the boiler will display the F62 error code. It could be that the gas valve is remaining wide open, partially open, or opening at the wrong times – any of the above could be potentially dangerous.

How dangerous is a faulty gas valve?

A gas leak is dangerous in any circumstance. When your Vaillant boiler detects gas escaping through the gas valve it will show the F62 error code and lockout. This means the boiler will lock out to a safety shut off and not work until the issue has been resolved by a gas safe registered professional.

It may be possible to intermittently reset the boiler and clear the fault allowing the boiler to work for a while, we would still strongly advise you to get the fault checked as it’s potentially a very dangerous situation.

If you smell gas, turn off the gas supply and your boiler and call the gas transporters emergency line on 0800 111 999.

Fixing the Vaillant ecoTEC F62 Fault

Before being able to fix the fault, your Heatsy Vaillant boiler repair engineer will first need to find the cause, there are several possible reasons why you’re seeing the F62 error and none of them are easy home fixes.

In some cases when your Vaillant boiler displays a fault code you can just increase the pressure or bleed the radiators, unfortunately, the Vaillant F62 fault code is not one of these instances and it must be rectified by a gas safe registered boiler repair engineer with suitable experience and qualifications.