Curious about boiler fan failure symptoms

[Lee]

Vaillant Turbomax non-condesning. Just changed a *slightly* noisy fan, slightly rumbly for no more than

2-3 seconds when first spun after a few hours inactivity, otherwise apparently fine. Have heard far worse in an otherwise working boiler!

But it has also cured the problem of the boiler not always firing successfully on first attempt and I'm wondering if this is just coincidence or whether there is some mechanism that I fail to understand? Far as I can see the fan was still spinning at normal speed, though without a tacho I suppose that's just an assumption ;)

I can follow that maybe it took longer to get to speed, but it really wasn't *that* noisy and it spins freely with only the barest of slop in the bearings, compared to the new one.

I guess I've answered my own question there, but just curious really :)

Lee

[John Rumm]

Sounds like it was waiting on a tellback from the air pressure switch as a part of the ignition sequence - and sometimes not getting it in time.

No doubt Geoff will be able to offer some input...

[Brian Gaff]

Ah, you have disturbed something like a dead spider or other oddball item that has made it work.

Brian

[geoff]

In message , Lee writes

At the end of the day, it depends on how long it is taking to activate the air pressure switch

Therre are three different versions of the turbomax made by three different manufacturers all with different designs

[Lee]

On the failed ignition attempts it failed to light after sparking, but always lit on the second attempt which is why I (obviously wrongly) assumed the fan was ok.

Still it seems to be igniting first time now, I would have changed the fan much earlier if I'd known it was responsible ;)

Fwiw Turbomax 828e, square outlet.

Lee

[geoff]

Then you have "disturbed" something

You will only get sparking after the air pressure switch has transferred which confirms to the pcb that the fan has developed sufficient differential pressure. That it is sparking is telling you that you are past the stage in the sequence where the fan has any further influence