My boiler has been temperamental for some time, so my water goes from hot to cold & back, now the central heating has started doing the same. The fan appears to be ok. Have notices that when there is more air able to circulate, it comes on & will stay on. The flue is clear. Could this be something to do with the air pressure switch? how do you know if it is working correctly?

zoe, November 2009

You can test aps with a multi-meter. Set to ohms put black lead on cmn terminal and red lead on 'nc' (three pin switch) should get a steady reading. No reading then switch is dead.
If two pin switch put red lead on 'no' pin. You should get no reading, if you do switch is dead.
If you find switch is ok test air flow to switch with a digital manometer - should be at least 2 mbars. If it isn't then the venturi inside the flue elbow will be blocked.
Remove elbow and clear blockage.

Nige, December 2009

Hi,

Had the same problem myself and found the answer posted on another site. It will involve a small amount of DIY but will save you pounds if it works!

1. Turn off gas supply (red tap underneath boiler) and elctrical supply (fused switch, to side or above/ below boiler) Undo screws on main cover and remove.
2. Undo 4 screws on metal cover facing you (has burner window hole on it).
3. Look to the top of the boiler and you will see the fan and a copper coil.
4. By the copper coil is two electrical connections. Behind and to the side of these connections is a further single connection which should have green/yellow wiring.
5. Carefully pull of the connector and blow inside to remove any dust, wipe the connector pin free of dust/dirt and replace.
6. Try the same for the two connectors by the front near the copper coil.
7. Replace all screws/covers in reverse order.

This worked for me and saved me calling an expensive engineer.

Good luck

Adrian S, December 2009

check the venturi inside the fan for blockage or debris, check the plastic pipes (1 clear and 1 red ) arent blocked or kinked, does the fan keep starting and stopping ?.

silverfox, November 2009