Air pressure switch

only been in the heating game 3.5 yr. another yr or so and i should have elec training and quals.therefore ill be able to test correctly and diagnose faster.

I understand your want to help /but as novice
you cannot an you are doing your best ....
are you doing a proper course ... or micky mouse one as usual ...!


Are you at a college , ???????, a proper NvQ , old School College ???not these sh*thole rat cesspits ....?

well done , how far on now with nvq 2 ????

Nice to see someone getting to the point instead of the usual dancing around the fact ``that they do not know `` routine..How bleedin` straightforward was that??

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No more or less straightforward than the previous descriptions. You'll have trouble doing it if you can't get your meter probes to the connector - like you said you couldn't before. If you poke your probes into the connector holes you'll probably bend the contacts inside so it won't work again.

If you want to test an aps you need to know what pressures it switches closed, then open at, for which you need a digital manometer, and a T piece for the hose. Connect one branch to the meter and one to the switch. You can increase the pressure gradually by blowing gently at or compressing a long rubber hose on the third branch until you hear the click and see the resistance change. Check the resistances, both open and closed. Nominally they should be infinite and zero, in practice 100k+ and a couple of ohms or less. Sometimes they're inconsistent so it's hard to be sure. You never know how fussy a boiler's going to be.

But by measuring voltage "live" across the pins on the pcb like I suggested you're testing whether the thing works in the boiler, with the fan, venturi, hoses etc too. All of which would give the same symptoms exactly. There should be as near as dammit zero volts across the switch pins when it's closed. Fans get dirty and produce less pressure. Aps's drift as well. Quite often a dirty fan will operate a new aps but not an older one. Yours might only have needed the fan cleaning. I found a clogged fan on a fairly new boiler where there had been a lot of building going on outside - the dust had got to it. Also, if you did an aps-only test and found it ok, you'd be guided to change the pcb when it could just be a dirty venturi.
You could tell which it is by measuring the pressure the fan's generating, again with the digi manometer. Usually the operating pressure(s) of the aps is/are stamped on it, and usually there's a good margin extra, so if it's a 0.7mbar switch and the fan's only just making it at 0.9, you know to clean the fan/venturi/tubes and check the flue fitting.
Sometimes you can't measure the pressure the fan's making because the boiler cover's off - you have to see how things are arranged to see if it's one of those or not.
Again, if you've got an adjustable new aps you can bung it in set at different pressures. If the boiler doesn't work with it at 0.1 mbar then it's not the aps which is faulty.

ive got acs and corgi. i just need elec and more diagnostics.i work alone with an app so its not like i can gain knowledge from workmates. i learnt originally whilst at a large heating firm.ive done a bit of work in your neck of the woods due to word travelling

ChrisR said:

No more or less straightforward than the previous descriptions..........................Again, if you've got an adjustable new aps you can bung it in set at different pressures. If the boiler doesn't work with it at 0.1 mbar then it's not the aps which is faulty.

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Priceless stuff! I don't know about the rest of you guys but when ChrisR comes up with such detailed and comprehensive descriptions of how a really dedicated and experienced professional would do our work I copy it into my Technical Support file. Where else could we get that calibre of technical advice?

chrishutt said:

I don't know about the rest of you guys ... I copy it into my Technical Support file.

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You betcha! I can only think of one forum member who might claim to know more than ChrisR, but I doubt that he does and he certainly can't put it across successfully.

Plenty of people on here are far more knowledgeable than me, particularly on specifics. I've got a big directory full of clippings from forums. A lot of pro's keep their knowledge to themselves, which I can understand, but I've learned a lot from forums, and offline from some of the people who contribute.

Your modesty does you great credit ChrisR, but I quite carefully used the word "claim".

I'm a half-wit and even I could now test an APS following the explanation from Moz and my work has nothing to do with boilers.

Why follow this forum - I'm a stifiled whatever you guys are!

Moz - theres a very nice man hiding under that craggy exterior!

Fin said:

Moz - theres a very nice man hiding under that craggy exterior!

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You wouldn't say that if you'd seen some of his posts, including a particularly nasty one he posted last night but then deleted (it now reads "SORRY"- he should be).

I would even though he has called me a c**t previously because there is nothing that suggests more character in a human being than a genuine wish to help gratis.

The same could be said for many others on this forum.

Fin

with fan running set multimeter on ohm,s scale, place red probe on c and black ptobe on no there should be a reading of about 277 ohm,s.
Then place the black probe on nc and red on c it should read o.l

With boiler turned off, red probe on c and black on nc there should be a reading with meter set on continity (buzzer).