how do i check an air pressure switch is working on a combi? is it sufficient to blow down tubes and listen for click?
air pressure switch
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with power off nc+c should read read closed circuit on volt meter if not replace.
also turn power + gas off remove wires connect v meter switch power back on turn tap on to start the fan and there should be continunity between c+ no
you can also check if the aps is working if you take a 230 v ac reading from the overheat stat put one probe on a terminal on the overheat stat
and one on a neutral wire if you get 230v your aps is working
and if you can see it sparking it is also working
+++++++++++++++++++++++++++++++++++++++++++++++
you could take it of and connect a v meter and blow gently on see if it goes to conti if it does its ok
MOD
see 10 a
also turn power + gas off remove wires connect v meter switch power back on turn tap on to start the fan and there should be continunity between c+ no
you can also check if the aps is working if you take a 230 v ac reading from the overheat stat put one probe on a terminal on the overheat stat
and one on a neutral wire if you get 230v your aps is working
and if you can see it sparking it is also working
+++++++++++++++++++++++++++++++++++++++++++++++
you could take it of and connect a v meter and blow gently on see if it goes to conti if it does its ok
MOD
see 10 a
I would be very concerned about telling someone to use a voltmeter when it needs to be a resistance meter AFTER the power has been disconnected and the APS removed from circuit. The resistance on closed contacts should be less than one ohm. Also since its a safety device concerned with gas safety I would normally recommend a CORGI registered person should be involved.
I always tell our trainees to blow TOWARDS the APS not into it because its very delicate and blowing into it can damage the thin diaphragm. I would also recommend measuring the actual operating point with a manometer.
Tony Glazier
I always tell our trainees to blow TOWARDS the APS not into it because its very delicate and blowing into it can damage the thin diaphragm. I would also recommend measuring the actual operating point with a manometer.
Tony Glazier
Quite often the hysteresis drifts from what it should be. You can just about measure it with a digital manometer but unless you happen to have a new switch to compare with for that particular model, the figures may not be too useful. Only the "close" pressure is given on the side.
The "drift" can lead to various symptoms , depending on the boiler. Some faulty APS's make fuses blow!
The "drift" can lead to various symptoms , depending on the boiler. Some faulty APS's make fuses blow!
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what i mean by volt meter is a multimeter with it set on k ohm scale and i also quoted to remove aps switch from circuit by disconnecting the wires to the apsAgile said:
can you tell me what you mean by blowing towards the aps i know about
the delicate diaphragm and how would you use a manometer to measure the oprating point thanks
and come to think of it why would you want to use a manometer when the best tool for the job would be a multimeter
or would be be to big. There are actually water manometers with an inclined tube at about 30* angle with an expanded scale that are fine for use on APS although your digital manometer is probably more convenient.
John will know these as they are/were used to measure flue draft on commercial boilers.
As Chris says its not just the switching presssure its the hysteresis which is important.
I once found one which switched off when the boiler modulated to low flame even though it was a constant speed fan. On test the hysteresis was less than 0.1 mb.
Its also sensible to do a tightness test on them because the diaphragm may be letting by if somebody has blown directly into the inlet.
Tony Glazier
John will know these as they are/were used to measure flue draft on commercial boilers.
As Chris says its not just the switching presssure its the hysteresis which is important.
I once found one which switched off when the boiler modulated to low flame even though it was a constant speed fan. On test the hysteresis was less than 0.1 mb.
Its also sensible to do a tightness test on them because the diaphragm may be letting by if somebody has blown directly into the inlet.
Tony Glazier
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