I've been working with a shared Waters 2695 with a 2996 DAD for the past year, and another user pumped 0.2M phosphate buffered mobile phase through the instrument (with their column) about 6 months ago. This change in mobile phase originally manifested as over-pressure issues, but copious flushing with warm water and isopropanol—and backflushing my column—eventually solved those issues & the instrument has run without fault for the past 4 months.

However, I am now getting a "Plunger Homing Fault (0)" error popping up twice during the instrument's self-initialization. Once before carousel initialization (which can be dismissed) & permanently afterwards. Unfortunately the initialization is required for any direct control of the instrument. This particular error message is not described in the 2695 Separations Module manual, however the Waters support website describes this error appearing after using buffered mobile phases.

Despite the Waters support article, I'm not inclined to believe residual buffers suddenly precipitated out of thoroughly flushed fluidics, 6 months after the buffer was run through the system, and after 4 months of flawless operation without any of the previously observed pressure issues. My first fixes for this error were loosening the actuator vent during initialization, and replacing the inline filter element. Neither of these steps solved the error popup.

Other culprits discussed on other chromatography forums seem to point to a faulty F1 fuse on the solvent management system board. I tested the existing one with a multimeter and got very inconsistent resistance readings, but replacing the fuse did not solve the error during initialization.

I checked my seal wash line's prime and it appears to not have any bubbles trapped in it. Presumably it's been washing the back sides of the actuators' plungers, however being locked out from direct control, I can no longer re-prime the seal wash line.

Some other culprit parts that I've found discussed online are:

• opening either the V2 or V3 valves manually
• Cleaning the primary—aka "(0)"—actuator, which would require laborously removing & disassembling that unit.
• Inspecting the check valve on the primary piston. My understanding is this is a very dust-sensitive part due to the sapphire check ball's tight tolerances for sealing shut.

Has anyone encountered this error before? What solution worked for you? I'm very much hoping I won't need to bring in a technician to rebuild the primary actuator but thinking it might come to this.

u/Micusil911: It has happened to me, usually because of the salts coming out of solution as you say after a power outage or something the only real solution is:
Change the check valve as you mentioned

But if in a hurry a workaround is to open the dry purge valve until the initialization is complete, after that wash your system through
Hope it helps

Thanks for the suggestions! I opened the dry purge valve about 5 full turns & initialized the HPLC, but it still threw the error twice: once before the carousels were initialized & once after.

I'm glad you think it's the check valve since that is a much easier replacement versus disconnecting & pulling out the torpedo tubes. Did you attempt to clean the check valve by sonicating in water or methanol? Or did you simply replace the part with a new OEM check valve?

u/Micusil911: I use a mixture water methanol 3:1 and sonicate until the sapphire ball rattles when shaken, otherwise replace it

u/liquidswords10304: 0 indicates problem with primary pump head. (I forget if right or left side is primary) Take it apart and clean piston/plunger, it can’t find home. Squirt di water in there on plunger and seals, it might be caked with buffer.
Also check for pinched waste tubing to waste bucket. I think you can open V2 and V3 valves manually on alliance front panel.

Looks like the right side (when facing the front of the instrument) pump is the primary, left is accumulator.

I looked through the separations module operator's guide for what the commands to open V1 to V4 are, but for the life of me I can't find it! Pressing the "Menu/Status" button shows the open/closed status of these valves, but I'm unable to use the arrow keys to select any of these icons, unlike directly changing gradient, flow rate, etc. The "direct function" tab accessible from the "Menu/Status" page never mentions valve control either.

Do you know what button presses must be navigated to be able to manually open the valves? Thanks for the help!

u/liquidswords10304: Good advice! Never throw out a CV without sonicacting first to see if ruby ball rattles. If it rattles, it will work.

u/Level9TraumaCenter: I wonder if phosphoric acid would work as a last-ditch attempt to save a valve, when no replacement is handy.