Your boiler will not light, and
it is probably not the part you are dreading

An ignition fault means the boiler tried to light and could not confirm that it did. There are about five things that cause it, two of them cost nothing to rule out, and the expensive ones are the last two on the list. It is worth going through them in order.

First: is the gas actually on

This sounds too simple to be worth saying, and it is one of the most common things we find.

We have been to jobs where the gas had been turned off by mistake. The meter is often tucked away under the stairs, and if somebody has been putting a vacuum cleaner in and out of that cupboard it is very easy to catch the lever on the emergency control valve without noticing.

The other one happens at the boiler itself. There is usually a gas lever underneath it that closes by hand, and we have been called out to boilers that would not light because somebody had been reaching about under there looking for the filling loop to top up the pressure, and closed the wrong lever.

So before anything else, look at both. The lever should be in line with the pipe, not across it.

Second: the condensate pipe

Every condensing boiler drains a small amount of water away as it runs, and if that pipe is blocked or frozen the water backs up and the boiler stops. In cold weather this is extremely common.

You may hear a gurgling noise from the boiler before it locks out, and that gurgle is worth paying attention to because it is often the only warning you get.

If the pipe is frozen and you can reach it safely from the ground, warming it gently along its length will usually clear it and the boiler will often restart.

Third: the flue

A blockage in the flue, for whatever reason, will cause an ignition fault. This is not something to go poking at, but it is on the list of things we check, and it is worth knowing that a flue problem shows up as an ignition fault rather than as anything obviously flue-shaped.

Fourth: the gas valve

Here we are into engineer territory. The question is whether the boiler is getting enough gas and whether the valve is opening properly when there is a demand for heating or hot water. That needs testing rather than looking at.

Fifth: the ignition side

The electrodes have to be in good condition and correctly positioned, and the cables and harness running to them have to be sound. A harness can be checked with a multimeter, and that is generally where we find the answer when the first four have come back clear.

And then the PCB

Last. Not first.

The reason we go through it in this order is that the first two cost nothing and take a minute, and the last one is the most expensive part in the appliance. Working backwards from the expensive thing is how people end up paying for a board when the gas lever was off.

The fault codes

Different manufacturers give this fault a different code, and it varies by model within a brand as well.

On a Vaillant an ignition fault shows as F28 or F29. On a Baxi it is E133, and on their newer models E.01.04. On an Ideal it is L2. Other manufacturers use their own codes, so it is worth checking the book that came with your appliance, or the panel inside the case.

The code tells you what the boiler could not do. It does not tell you which of the five things above caused it, which is why the order matters.

When to call someone

The first two on this list are yours. Everything from the flue onwards is a Gas Safe job, and the ignition side in particular involves working on the gas carrying parts of the appliance.

You can check an engineer's registration at https://www.gassaferegister.co.uk

Quick answers