hi.
I have a Ariston microgenus boiler which is a few years old.
It doesnt ignite now. The Fume sensor light comes on, but there are no
other indications of a problem from any other sensors besides it doesnt
come on.
I also cant see the pilot light through the hole at the front.
There was no intermittant problem or indication of a problem before.
Girlfriend reckons theres a hissing noise coming from it that wasnt
coming from it before; the hissing noise remains when the gas is turned
on and whenit is turned off.
Is this likely to be a serious problem or just a simple ignition thing
i might be able to fix myself?

Thanks to anyone who might be able to help