Does any one know why air presure switch have 2 air tubes, one is plus prssure and one is negtive pressure. My boiler stops firing when the negtive pressure tube is connected. The boiler fire up fine if it is not connected. The negtive tube and venturis are not blocked. What is the danger without it?

L.P, October 2007

you need to correct your pressure of the central heatings. It should be between 1 to 1.5 m bar. The correct level should be able to operate the boiler

domestic engineer

anjum zaman, October 2007