what is the reason that water keeps coming out of pressure relief valve on the over flow pipe, not all the time, every now and then, is the valve bad and should i replace it.

The pressure relief valve is a safety device for when there is a potential danger due to rising internal water pressure.

Consider the practicality of changing out a smoke detector if and when it goes off.

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Yes, you really have to find out the MAKE and MODEL to get good answers. There IS more than one machine made.