air pressure switch

[gasman12]

Like I said, I'd figure it out - didn't take nearly as long as anticipated - no wonder you are all so protective - charging so much to fix a simple switching system - that's all it is - makes no difference if its fans, motors, valves or solenoids, its just a switch. Just thought that someone might have saved me a couple of hours, that's all.

 

[picasso]

go on then hows it work?

 

[holty]

no wonder you are all so protective - charging so much to fix a simple switching system

nothing protecive about it.and we charge for diagnosing a faulty boiler.id love to see a 90 year old granny, holding a multimeter and usuing a manometer then turning round and saying simple fault. easy.

 

[kevplumb]

it switches the fan on

jeez another thick brit

 

[davebgas]

3 wire, pcb sends voltage to aps, sends back to confirm 'no air' then pcb sends voltage to fan and also again back up the aps common. Pressure change over aps causes the diaphragm inside to make a microswitch sending voltage back to pcb to confirm fan running. Ignition commences.

2 wire is just a bog standard change over switch. Doesn't confirm a 'no air' situation.

 

[Axel]

...the point being that if (on a 3 wire system) the aps was faulty and permanently stuck in closed position, then the ignition sequence would be halted, preventing a false positive interpretation of the aps.....