F28 Error Code On Vaillant Ecotec Combi Boiler

Today, I had what seemed like a pretty standard callout to a Vaillant Ecotec Plus 831 combi boiler in Greenhithe. It was showing an F28 fault code.

This code means that the boiler tried to light unsuccessfully 3 times in a row. It does this as a safety measure to stop a dangerous mixture of unburned gas building up in the boiler.

Common Causes Of Vaillant Ecotec F28 Faults

No Gas

Yes, one of the most common reasons for your Vaillant to show an F28 code is because there’s no gas to your property. Reasons for this include gas works on your road, someone accidentally turning off the gas at the meter, or credit on a prepay gas meter running out.

If you have another gas appliance (like a gas hob or gas fire) you can try to light them. If they don’t light, it means there’s no gas to your appliances. So the problem isn’t with the boiler, it’s with your gas supply.

Faulty Spark Electrodes

Spark electrodes are a bit like spark plugs in a car. They create a spark near the burner and light the gas when the boiler turns on. These can crack or lose continuity which will stop them from making a spark and lighting the gas. This will create an F28 fault.

Broken HT Lead

The lead that connects the spark electrode the boiler’s circuit board (also called PCB) can also break. Again, this will prevent the electrode from making a spark, which will stop the boiler lighting and cause an F28 code.

Gas Valve Fault

This is more of an issue on more recent Ecotec’s from about 2012 onwards. Their gas valves seem to fail more often than on the older models. I (or any other good heating engineer) can test to see if the gas valve is opening at the right time by doing a simple pressure check.

So what was caused the problem?

On this particular boiler, I changed the spark electrode because it was in such poor condition, but it wasn’t the cause of the F28 fault.

The cause was the spark generator on the circuit board (PCB) – see picture.

You can see the spark generator as the grey plastic square on the right hand side of the PCB.

This was only working occasionally, so most of the time the boiler wouldn’t light, but sometimes it would, which made it quite hard to diagnose.

You can replace just that part of the PCB, you need to replace the whole thing.

To help save the customer some money, I bought a reconditioned one from a boiler pcb reconditioning specialist, which saved them about 50% on the price of a new one – and it still comes with a 1 year warranty.

This solved the problem instantly (and saved the customer about ?100 on the cost of a new PCB).