Boiler air pressure switch

[Pete Verdon]

Morning,

Over the last few days, I've been getting an intermittent fault in my boiler (a Chaffoteaux Brittony combi). The code it blinks translates to "fan on but air pressure switch not activated", or words to that effect. Turning the power off and on again (can you tell I'm a software engineer? :-) ) clears it for some hours / up to a day.

I have the service manual for it, and can see that the air pressure switch and venturi (and the fan) is mounted inside the "sealed chamber" (but not in the combustion chamber itself). I'm satisfied with my competence to open this up (and in any case it's not actually gas-carrying) but I'm not sure what I'd do when I get there if nothing's obviously damaged.

It seems to me that the switch is not necessarily the culprit - it could be doing its job perfectly and warning that the pressure is not changing due to some other fault. So I don't want to just order another switch and slap it in.

Any suggestions on how to proceed?

Cheers,

Pete

[BigWallop]

This type of thing can be caused by the change in weather, and having wind blow back into the flue and cause false detection. You say that a power cycle sometimes clears it, or is it coincidence that your power cycle coincided with a drop in the wind, or even the direction changed.

For me, it's a difficult one to diagnose unless you are standing in front of it, I'm afraid. I hope other more knowledgeable souls come along with a few more suggestions for you to try.

[Cicero]

========================================= Blow through the air switch tubes - might be a bit clogged up with dust. It might not work but at least it can't do any harm.

Cic.

[geoff]

In message , Pete Verdon writes

You could always check the APS

Check the closed and open contact resistance - you want it to be in the region of an ohm or less, this involves checking your probe resistance first. You can activate the APS by GENTLY sucking or blowing on one of the rubber tubes to the APS. Kink the tube and leave it kinked for 30 seconds or so to check that the APS membrane is not ruptured.Also check for a split or suchlike in the rubber tubes

check the seals, check the flue,

Are you experiencing the high winds we are getting around here ? If your flue is exposed, you might be getting blowback

[geoff]

Well yes it can

you can rupture the APS diaphragm

[Cicero]

========================================= I meant *disconnected* tubes and should have said so because I wouldn't ever suggest blowing dust *into* any piece of equipment like a switch. Thanks for pointing out the possibility of damage to the switch and I should add the possibility of blow-back of dust into the blower's eyes.

Cic.

[Pete Verdon]

It's a fair point - without the warning I quite likely would have blown through the valve body. I'd hope that I have sufficient mechanical sympathy not to rupture anything in the process though, unless these diaphragms are unusually sensitive.

At the moment, I'm hoping it's just the wind direction as BigWallop and Geoff suggested :-). It hasn't happened again since I posted.

Pete

[[e-mail]]

Blowing through the tubes works for me...but how do I solve the problem long term? I'm doing this every other day

[Fredxx]

Before replying to an 13 year old post from a broken website, please read and digest this:

[Brian Gaff (Sofa]

The implication though is that this is still an issue and he just happened to see he temp solution. However when you do this on the web site which shall not be named, you really do need to quote te original post with the data of the boiler and other info or nobody outside of the web site will have any clue of what you speak!

Brian

[John J]

I've not heard anything from Geoff for years. Does anyone know if he's ok?