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My first guess is that there is an in fluent valve closed, or partially closed. 2nd guess would be an obstruction in the pump or the pump not properly working.

It sounds like the o-ring on the light ho0using isn't sealing - pull the light out, fully dry it and lube and properly seal the light. (info on this can be provided )

I'll help as I can but, I'm really busy at this time, please bear with me.