Gazza my system is 7 years old 200 gpd ro-man
Can't remember when/if ever i changed membranes
I will do this later in week, i'm ordering pressure gauge tonight as my one kaputt on RO, probably when froze up
Your membranes are newish then, has your RO froze up in cold spell, maybe membranes got frost bite.
You say waste water is alot more.
Could something be wrong with flush mechanism stuck in flush mode even though looks ok (mine has blue tap on Ro, when in 12 o'clock position ro production 9 0'clock flushing.
Did you disconect ro during big freeze and maybe pushed tubing into wrong john guest fittings (so somethings back to front?)
Sorry Gaz, sure not case just thinking out loud.
Good luck; let us know what it was as might happen to me.
Hope to sort mine this week.
Ps. if using 2mm pencil jets, maybe switch to fan jets or 1mm pencils Gardiners sell both I know doesn't solve ro, but you'l use less water.
Goodluck
Lee